J Cataract Refract Surg 2003; 29:322–328
Magda Rau, MD, Dieter Dausch, MD
Purpose: To evaluate the efficacy, predictability, and stability of refraction obtained after intrastromal corneal ring segment (ICRS) implantation for low to moderate myopia
Setting: Single-center clinical practice.
Methods: In this prospective 2-surgeon study, 9 patients (15 eyes) with low to moderate myopia were recruited to receive ICRS implants.
Results: At 1 day, 10 of the 15 eyes had an uncorrected visual acuity (UCVA) of 20/40 or better. At 12 months, all eyes had this UCVA and 66.6% had 20/25 or better. The mean manifest refraction stabilized after the first week at <−0.5 diopter (D). At 12 months, all eyes were within ±1.0 D of the intended manifest refraction; 67% were within ±0.5 D. Sixty percent of eyes had no change from the preoperative best corrected visual acuity; 13.3% improved by 1 line, and 26.6% lost 1 line. The postoperative complications included lamellar channel deposits (n = 12), ICRS dislocation (n = 2), corneal infiltrates (n = 2), bleeding in the positioning ring hole (n = 1), 0.3 mm segment decentration (n = 1), and prolonged wound healing (n = 1).
Conclusions: Intrastromal corneal ring segment implantation for the correction of low to moderate myopia afforded good visual recovery and efficacy similar to that with laser in situ keratomileusis and superior to that with photorefractive keratectomy. However, light or blunt trauma and insufficient hygiene can have serious consequences and there is the potential for induced astigmatism. Corneal infiltrates can occur and must be treated immediately. The ring implantation technique is demanding. Advantages of ICRS implantation include rapid and stable visual recovery as well as reversibility.
J Cataract Refract Surg. 2005 Dec;31(12):2356-62.
Brown SM, Freedman KA. Cabarrus Eye Center, Concord, North Carolina 28025, USA. sbrownmd@carolina.rr.com
PURPOSE: To determine whether the currently accepted method of selecting a minimum optical zone diameter for laser refractive surgery that is equal to or slightly greater than the dark-adapted pupil diameter provides a sufficient diameter of corneal surface to focus light arising from objects in the paracentral and peripheral visual field.
SETTING: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA.
METHODS: An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from an object through the physical pupil (PP). This model incorporates the patient variables of central anterior chamber depth (ACD), central corneal curvature (K(c)), and the diameter of the apparent entrance pupil (EP). The model was expanded to incorporate distant objects off the line of sight (LOS), described by their angular displacement from the fixation object in visual space (the object tangent angle delta(ob)). Results were calculated for the 360 meridian degree visual field (ie, for all objects in visual space perceptually displaced from the fixation object by angle delta(ob)). The effect of the prolate nature of the cornea was also investigated.
RESULTS: The ECRD expanded rapidly as a function of PP and delta(ob) but was minimally influenced by K(c). Beyond a critical object tangent angle delta(c), light rays striking the corneal vertex were not refracted through the PP, and the ECRD became an annular surface centered on the corneal vertex. The delta(c) was not a function of K, but increased as the PP increased and decreased as the ACD increased. The prolate nature of the cornea had little influence on the ECRD, even for very peripheral light rays.
CONCLUSIONS: The ECRD expands rapidly when considering distant objects only slightly displaced from the LOS. A patient treated with an optical zone equal to or slightly greater than the dark-adapted pupil diameter may experience vision quality loss for paracentral and midperipheral objects even under conditions of ambient indoor lighting.
The importance of pupil size measurement, and anterior chamber depth…
“What good is making pupil size measurement a part of the standard of care if it is never utilized (by the doctor, or to communicate to the patient the risks it implies about the surgery they are considering)?
It’s a (kind of sick) joke.
Couple that w/the size of the correction AND with VERY deep anterior chambers (think about the notion of an ‘exit pupil’ taught in most classical physics classics as it pertains to optics – it is obvious that the farther away the ablation from the point of lens focus, the larger that ablation need be). Forget about it – I was guaranteed to have a miserable outcome.”
Patient , age 23, with smeared vision and debilitating dry eye as a result of Custom Vue LASIK on the VISX S4
Schmack I, Dawson DG, McCarey BE, Waring GO 3rd, Grossniklaus HE, Edelhauser HF.
Emory Eye Center, Emory University School of Medicine, Atlanta, GA 30322, USA.
PURPOSE: To measure the cohesive tensile strength of human LASIK corneal wounds.
METHODS: Twenty-five human eye bank corneas from 13 donors that had LASIK were cut into 4-mm corneoscleral strips and dissected to expose the interface wound. Using a motorized pulling device, the force required to separate the wound was recorded. Intact and separated specimens were processed for light and electron microscopy. Five normal human eye bank corneas from 5 donors served as controls. A retrospective clinical study was done on 144 eyes that had LASIK flap-lift retreatments, providing clinical correlation.
RESULTS: The mean tensile strength of the central and paracentral LASIK wounds showed minimal change in strength over time after surgery, averaging 2.4% (0.72 +/- 0.33 g/mm) of controls (30.06 +/- 2.93 g/mm). In contrast, the mean peak tensile strength of the flap wound margin gradually increased over time after surgery, reaching maximum values by 3.5 years when the average was 28.1% (8.46 +/- 4.56 g/mm) of controls. Histologic and ultrastructural correlative studies found that the plane of separation always occurred in the lamellar wound, which consisted of a hypocellular primitive stromal scar centrally and paracentrally and a hypercellular fibrotic stromal scar at the flap wound margin. The pathologic correlations demonstrated that the strongest wound margin scars had no epithelial cell ingrowth-the strongest typically being wider or more peripherally located. In contrast, the weakest wound margin scars had epithelial cell ingrowth. The clinical series demonstrated the ability to lift LASIK flaps without complications during retreatments up to 8.4 years after initial surgery, correlating well with the laboratory results.
CONCLUSIONS: The human comeal stroma typically heals after LASIK in a limited and incomplete fashion; this results in a weak, central and paracentral hypocellular primitive stromal scar that averages 2.4% as strong as normal comeal stroma. Conversely, the LASIK flap wound margin heals by producing a 10-fold stronger, peripheral hypercellular fibrotic stromal scar that averages 28.1% as strong as normal comeal stromal, but displays marked variability.
http://www.fda.gov/foi/warning_letters/g5316d.htm
RETURN RECEIPT REQUESTED
FLA-05-27
Dear Mr. Woodrell :
The above-stated inspection revealed that this device is adulterated under section 501(h) of the Act, in that the methods used in, or the facilities or controls used for, the manufacture, packing, storage, or installation are not in conformance with the Current Good Manufacturing Practice (CGMP) requirements for medical devices which are set forth in the Quality System regulation, as specified in Title 21, Code of Federal Regulations (CFR), Part 820. Significant deviations include, but are not limited to, the following:
Data downloaded from LADARVision systems currently in use in the U.S. showed significant differences in the retreatment requirements between patients treated prior to 15 minutes after calibration of the device as opposed to patients who were treated after 15 minutes following calibration of the device. Another table was provided that used the points of < 30 minutes from calibration to treatment and > 30 minutes or more from calibration to treatment.
Your response to this data has been inadequate. There is a note to a warning to the device user manual, which states, "WARNING: System calibration must be done between patients and within 15 minutes of surgery, failure to perform calibration in the time frame indicated may result in improper orientation of the ablation. " However, there was no reason provided to explain the use of these times. Moreover, the note to warning is not by itself sufficient to address the seriousness of this problem . (FDA 483, Item #1)
Class code - 801: Laser not firing,
Class code - 802A: Loss of tracking, and
Complaint records associated with these complaint class codes are not adequately reviewed, evaluated, and investigated to determine the root-cause of the system and/or sub-assembly component malfunction (FDA 483, Item #2).
a . Complaint Record RS030392 received on April 14, 2003, involving the LADARVision® 4000 Beta, lot number L4B1023S references the laser stopped firing during surgery at 92% complete. The Field Service Engineer (FSE) found arcing in the laser chassis assembly. The FSE adjusted components to prevent future arcing. The complaint record does not document and confirm that an investigation was conducted to determine the root cause of the reported problem. The record also fails to document the justification for not conducting an investigation and is not signed and dated by responsible personnel.
c. Complaint Record RS041047 received on August 11, 2004, involving a refurbished LADARVision® 4000 Beta, lot number L4B1090S referencing noise from the laser with a system failed error message. A similar complaint, RS030392 referenced a malfunctioning translator, which was replaced because of faulty/defective bearings. The complaint was classified as complaint class 823- Noise Coming from system. The complaint was more appropriately determined a translator malfunction, which is complaint class 833. The malfunction causes the laser to stop operating or firing resulting in surgery being terminated, causing under correction, which is not considered by your firm to be an injury.
e. Complaint Record RS031262 received on November 14, 2003, involving LADARVision® 4000 Beta, lot number L4B1022S references a laser unable to track. The FSE confirmed the failure mode and replaced the zoom motor. The Manufacturing Engineer (ME) confirmed that the motor performed erratically when operating under a torque and will not reverse direction when prompted by software. A similar complaint FS030539 (noted above) does not document that an investigation was conducted to determine the root cause for the zoom motor failure or the justification for not conducting an investigation into the malfunction.
4. Failure to establish and maintain procedures that define the responsibility for review and the authority for the disposition of nonconforming product as required by 21 CFR 820.90(b)(1). (FDA 483, Item #4). Your own procedures, specifically, SOP 7501-00.38, Field Returns, and SOP 7003-0909, Evaluation of Non-Conforming Parts Returned from Field Service, are not followed:
b. Complaint Record RS040031 - Per the referenced SOPs gas filters were not returned for evaluation and an evaluation was not performed. This report was evaluated by Product Safety (PS) and classified as a "Malfunction". Personnel experienced headache, dry tight throat, and nausea resulting in an emergency room (ER) visit.
The above-stated inspection also revealed that your device is misbranded under section 502(t)(2) of the Act, in that your firm failed or refused to furnish any material or information required by or under section 519 respecting the device. Specifically, your firm failed to report within 30 days whenever the manufacturer receives or otherwise becomes aware of information, from any sources, that reasonably suggests that a device marketed by the manufacturer has caused or contributed to a death or serious injury, as required by 21 CFR 803.50(a)(1).
a. Complaint Record RS041329
Your firm also failed to investigate adverse event reports and to evaluate the cause of the reported event as required by 21 CFR 803.50(b)(2). The following adverse event reports have not been adequately investigated as required:
b. Complaint Record RS041106
d. Complaint Record RS031262
f.. Complaint Record RS031146
h. Complaint Record RS031257
We have reviewed your response, dated February 3, 2005. We acknowledge that you have proposed to improve your complaint handling procedure. We would appreciate receiving the periodic reports that you have promised. Nevertheless, your response to the violations discussed above is inadequate because our review of the data shows that reviews, evaluations, and corrective actions were not fully assessed. Also your own procedures were not followed and misinterpretations were made as to the status of complaints that were reported and the conclusions that were drawn, which affected the corrective actions that were required. You should address each and every observation when responding to this letter. Your response has been made part of the Florida District file.
Please notify this office in writing within fifteen (15) working days of receipt of this letter, of any steps that you are still in the process of taking to correct the noted violations, including (1) the time frames within which the corrections will be completed, (2) any documentation indicating the corrections have been achieved, and (3) an explanation of each step being taken to identify and make corrections to any underlying systems problems necessary to assure that similar violations will not recur.
Sincerely,
Director, Florida District
Although promotional, this study was still done by Synovate
Excerpts from the full text:
Ophthalmology. 2002 Jan;109(1):175-87.
Sugar A, Rapuano CJ, Culbertson WW, Huang D, Varley GA, Agapitos PJ, de Luise VP, Koch DD.
Ophthalmic Technology Assessment Committee 2000-2001 Refractive Surgery Panel.
OBJECTIVE: This document describes laser in situ keratomileusis (LASIK) for myopia and astigmatism and examines the evidence to answer key questions about the efficacy and safety of the procedure.
METHODS: A literature search conducted for the years 1968 to 2000 retrieved 486 citations and an update search conducted in June 2001 yielded an additional 243 articles. The panel members reviewed 160 of these articles and selected 47 for the panel methodologist to review and rate according to the strength of evidence. A Level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a Level II rating is assigned to well-designed cohort and case-control studies; and a Level III rating is assigned to case series and poorly designed prospective and retrospective studies, including case-control studies.
RESULTS: The assessment describes randomized controlled trials published in 1997 or later (Level I evidence) and more recent comparative and noncomparative case series (Level II and Level III evidence), focusing on results for safety and effectiveness. It is difficult to extrapolate results from these studies that are comparable to current practices with the most recent generation lasers because of the rapid evolution of LASIK technology and techniques. It is also difficult to compare studies because of variations in the range of preoperative myopia, follow-up periods, lasers, nomograms, microkeratomes and techniques, the time frame of the study, and the investigators' experience.
CONCLUSIONS: For low to moderate myopia, results from studies in the literature have shown that LASIK is effective and predictable in terms of obtaining very good to excellent uncorrected visual acuity and that it is safe in terms of minimal loss of visual acuity. For moderate to high myopia (>6.0 D), the results are more variable, given the wide range of preoperative myopia. The results are similar for treated eyes with mild to moderate degrees of astigmatism (<2.0 D). Serious adverse complications leading to significant permanent visual loss such as infections and corneal ectasia probably occur rarely in LASIK procedures; however, side effects such as dry eyes, night time starbursts, and reduced contrast sensitivity occur relatively frequently. There were insufficient data in prospective, comparative trials to describe the relative advantages and disadvantages of different lasers or nomograms.
JOURNAL OF REFRACTIVE SURGERY 2007; 23(4):338
By Ilpo S. Tuisku, MD; Nina Lindbohm, MD, PhD; Steven E. Wilson, MD, PhD; Tim M. Tervo, MD, PhD
PURPOSE: To assess subjective symptoms and objective clinical signs of dry eye and investigate corneal sensitivity after high myopic LASIK.
METHODS: Twenty eyes of 20 patients with a mean age of 34±7.5 years who had undergone high myopic LASIK 2 to 5 years previously and 10 eyes of 10 controls with a mean age of 39.8±10.4 years were enrolled in the study. Clinical signs of dry eye and subjective dry eye symptoms were determined. The corneal sensitivity was assessed using non-contact esthesiometer.
RESULTS: The preoperative spherical equivalent refraction was –11.40±1.40 diopters (D) (range: –9.10 to –14.00 D) and the intended spherical equivalent refraction correction was –10.40±1.10 D (range: –8.30 to –12.50 D). Schirmer’s test score was 14.4±8.9 mm in patients and 9.0±4.2 mm in controls (P=.066). The break-up time was 15.9±11.2 seconds in patients and 14.0±10.0 seconds in controls (P=.505). The mean corneal sensitivity was 73.5±29.6 mL/min in patients and 78.0±18.7 mL/min in controls (P=.666). The majority (55%) of patients still reported dry eye symptoms. Ocular surface disease index indicating degree of dry eye symptoms was significantly higher in LASIK patients (18.6±13.4%) compared to controls (7.5±5.7%; P=.022).
CONCLUSIONS: The majority of patients who received LASIK for high myopia reported ongoing dry eye symptoms, although objective clinical signs of tear insufficiency and hypoesthesia were not demonstrable. We assume that symptoms represent a form of corneal neuropathy rather than dry eye syndrome. [J Refract Surg. 2007;23:338-342.]
J Cataract Refract Surg. 2005 May;31(5):922-9.
Loh RS, Hardten DR. Minnesota Eye Consultants, Minneapolis, Minnesota, USA.
PURPOSE: To report persistent unilateral flap edema following laser in situ keratomileusis (LASIK) in patients with asymmetrical central corneal thickness.
SETTING: Minnesota Eye Consultants, Minneapolis, Minnesota.
METHODS: Retrospective, noncomparative interventional case series.
RESULTS: We examined 6 eyes of 3 patients with asymmetrical preoperative pachymetry who developed persistent unilateral flap edema after uneventful myopic LASIK in the eye with thicker preoperative pachymetry. All cases had asymmetrical preoperative pachymetry with flap edema developing in the eye with higher preoperative mean central corneal thickness (CCT) values, preoperative mean CCT subject eye 622 microm (range 556-664 microm) versus fellow eye 583 microm (range 510-621 microm). There was no associated ocular inflammation or rise in intraocular pressure. Significant flap edema resolved on a combination treatment of topical steroid and hypertonic saline.
CONCLUSIONS: Laser in situ keratomileusis can cause temporary endothelial cell dysfunction or stress, which manifests as temporary flap edema and subclinical corneal thickening. The edema appears to be limited to the actual flap and there was no loss of epithelial integrity in these eyes and no clinically noticeable interface fluid. This new clinical entity appears to occur in patients with asymmetrical preoperative corneal pachymetry and is associated with postoperative specular microscopy abnormalities. In cases with unexplained asymmetrical corneal thickness, preoperative evaluation should include specular microscopy to evaluate for risk features that may increase the chances of a slower postoperative recovery.
J Cataract Refract Surg. 2006 Feb;32(2):255-60. Chaglasian EL, Akbar S, Probst LE. Illinois Eye Institute, Illinois College of Optometry, Chicago, TLC Vision, Westchester, Illinois 60616, USA. echaglas@eyecare.ico.edu PURPOSE: To compare scotopic pupil measurements obtained with a Colvard pupillometer with measurements taken with a printed pupil gauge and penlight with a cobalt blue filter attachment in mesopic and scotopic luminance.
SETTING: The Illinois Eye Institute, Chicago, Illinois, USA.
METHODS: Pupil measurements were taken of both eyes of 38 patients (76 eyes). Any subject presenting with anterior segment disease, fixed or dilated pupils, iris abnormalities, or a history of eye disease or eye trauma was excluded. At a mesopic luminance of 2.11 foot-candles, pupil measurements were taken with a Bernell pupil card and penlight with a cobalt blue filter attachment. At a scotopic luminance of less than 2.00 foot-candles, pupil measurements were taken with the Bernell card system and the Colvard pupillometer.
RESULTS: In mesopic luminance, the mean pupil diameter was 5.17 mm (range 3.0 to 7.5 mm) with the Bernell card method. The mean difference between the Colvard in scotopic luminance and the Bernell card system in mesopic luminance was -0.04 mm (P = .0831). In scotopic luminance, the mean pupil diameter was 6.32 mm (range 4.0 to 8.0 mm) with the Bernell card method and 5.13 mm (range 3.0 to 7.5 mm) with the Colvard pupillometer, with a mean difference of -1.18 mm (P<.0001). The limits of agreement between the mesopic Bernell card system and the Colvard pupillometer were small (-0.32 to 0.24), whereas the limits of agreement between the scotopic measurements of both techniques were large (-2.18 to -0.18).
J Refract Surg. 2006;22:441-447Ahmed Galal, MD, PhD; Alberto Artola, MD, PhD; Jose Belda, MD, PhD; Jose Rodriguez-Prats, MD, PhD; Pascual Claramonte, MD, PhD; Antonio Sánchez, MD, PhD; Oscar Ruiz-Moreno, MD, PhD; Jesús Merayo, MD, PhD; Jorge Alió, MD, PhDPURPOSE: To describe interface corneal edema secondary to steroid-induced elevation of intraocular pressure (IOP) following LASIK.METHODS: Retrospective observational case series. Diffuse interface edema secondary to steroid-induced elevation of IOP was observed after LASIK simulating diffuse lamellar keratitis (DLK) in 13 eyes. Mean patient age was 31.4±5.3 years. Patients were divided into two groups according to provisional misdiagnosis: DLK group (group 1) comprised 11 eyes and infection group (group 2) comprised 2 eyes (microbial keratitis). Mean follow-up was 8.1±0.5 weeks.RESULTS: In the DLK group, typical diffuse haze was confined to the interface and extended to the visual axis, impairing vision in all eyes. Provisional diagnosis was late-onset DLK and topical steroids were started. Repeat examination showed elevated IOP as measured at the corneal center and periphery using applanation tonometry (mean 19.1 mmHg and 39.5 mmHg, respectively), causing interface edema with evident interface fluid pockets. Steroids were stopped and topical anti-glaucoma therapy was started. The interface edema decreased and at the end of follow-up the corneal transparency was restored and IOP dropped to normal values. The infection group demonstrated a microbial keratitis-like reaction and underwent flap lifting and interface wound debridement and biopsy with administration of fortified antibiotics and steroids. After elevated IOP was detected, steroids and antibiotics were stopped and topical anti-glaucoma therapy was started, resulting in the resolution of the interface edema.CONCLUSIONS: Interface fluid syndrome secondary to steroid-induced elevation of IOP might develop in steroid responders after LASIK with a misleading clinical picture simulating DLK or infectious keratitis. Management includes stopping topical steroids and starting topical anti-glaucoma therapy.
Journal of Refractive Surgery Vol. 23 No. 6 June 2007
Sonal S. Tuli, MD; Sandhya Iyer, MD, FRCS
PURPOSE: To report a case of ectasia occurring >4 years following LASIK with no risk factors and a residual stromal bed >300 µm.
METHODS: A 33-year-old woman presented 4 years after LASIK with mild blurring in the left eye. Uncorrected visual acuity (UCVA) had been 20/20 in both eyes previously.
RESULTS: Uncorrected visual acuity was 20/20 and 20/40 in the right and left eyes, respectively. Best spectacle-corrected visual acuity (BSCVA) was 20/20 with –0.75 +2.25 X 70° refraction in the left eye, which matched topography. Preoperative corneal thickness was 595 µm, and topography showed no risk factors preoperatively or immediately postoperatively. Calculated residual stromal bed was 342 µm and measured 400 µm with ultrasound microscopy. One year postoperatively, UCVA decreased to 20/400, and BSCVA decreased to 20/60 with refraction of –4.50 +5.00 X 90°. The patient was intolerant of contact lens wear and is considering collagen cross-linking, Intacs, or corneal transplantation.
CONCLUSIONS: Ectasia can occur more than 4 years after LASIK. Its etiology is unknown and management is challenging. [J Refract Surg. 2007;23:620-622.]>
From the full text:
Quote: There was no documentation of intraoperative corneal thickness.
Quote: The posterior float on Orbscan increased to 55 μm (Fig 2). A Paradigm UBM microscope (Paradigm Medical Industries, Salt Lake City, Utah) was used to measure the residual stromal bed directly, which showed flap thickness of 150 μm and residual stromal bed of 400 μm.
Quote: This report shows that ectasia can occur >4 years following uncomplicated LASIK in a patient with no risk factors.
Quote: Confocal microscopy of corneas after LASIK have shown 20% loss of keratocytes above and below the flap interface by apoptosis immediately following surgery, which progressed to 40% at 5 years postoperatively.6 This loss of keratocytes has been seen in histology specimens of corneas removed during keratoplasty for ectasia.7 The decrease in keratocytes could progressively weaken the stromal bed and cause ectasia. It is conceivable that individual corneas differ in stromal keratocytes density, and the loss of keratocytes could cause ectasia in corneas with fewer keratocytes. Although most people develop ectasia much earlier, a weakened stromal bed may explain its development in our patient 4 years after LASIK.
Quote: Management of ectasia after LASIK is challenging due to its rapid progression. The use of contact lenses may correct vision but could be diffi cult to fi t, and patients may be intolerant due to dry eye, as was our patient.
Quote: One third of ectasia cases following LASIK require penetrating keratoplasty. 1 However, penetrating keratoplasty may result in unacceptable lifestyle changes in patients who often choose LASIK due to their active lifestyle. Also, a large graft may be necessary to include the entire LASIK flap and the donor cornea would be sutured to an intact recipient rim, which would increase risk of rejection. Other options are implantation of intrastromal rings (Intacs) and riboflavin with collagen cross-linking.8,9 However, these merely stabilize the cornea, and vision does not improve to the same levels noted before ectasia. In addition, cross-linking involves ultraviolet light, and its long-term effects are unknown.
JOURNAL OF REFRACTIVE SURGERY 2007; 23(3):312
By Farid Karimian, MD; Alireza Baradaran-Rafii, MD; Mohammad Ali Javadi, MD; Roshanak Nazari, MD; Hossein Mohammad Rabei, MD; Mohammad- Reza Jafarinasab, MD
PURPOSE: To report clinical manifestations and the bacteriologic profiles of three patients with bilateral bacterial keratitis following photorefractive keratectomy (PRK).
METHODS: Photorefractive keratectomy was performed for mild to moderate myopia or compound myopic astigmatism. Bandage contact lenses were fitted at the conclusion of each surgery. Bilateral infectious keratitis was diagnosed within 3 days after surgery. Smear and culture were obtained in all three cases. Patients were treated with topical fortified antibiotics (cefazolin and gentamicin).
RESULTS: All patients presented with severe bilateral ocular pain, photophobia, purulent discharge, and dense corneal infiltration. Causative organisms were Staphylococcus aureus (n=2) and Streptococcus pneumoniae (n=1). Ulcers were controlled with aggressive medical therapy in five eyes; however, tectonic penetrating keratoplasty was required in one eye.
CONCLUSIONS: Uncontrolled blepharitis and bandage contact lens use appears to play a role in the development of bacterial keratitis after PRK. Avoidance of simultaneous bilateral surgery in patients with risk factors for bacterial keratitis, preoperative control of blepharitis, and good contact lens hygiene is suggested. [J Refract Surg. 2007;23:312-315.]
J Cataract Refract Surg. 2003 Apr;29(4):825-31.
Viestenz A, Langenbucher A, Hofmann-Rummelt C, Modis L, Viestenz A, Seitz B.
Department of Ophthalmology, University of Erlangen-Nurnberg, Germany. Arne.Viestenz@t-online.de
PURPOSE: To evaluate flap dimensions and cut quality with repeated blade use of the automated Summit Krumeich-Barraquer microkeratome (SKBM [LadarVision]).
SETTING: Department of Ophthalmology, University Erlangen-Nuremberg, Erlangen, Germany.
METHODS: The SKBM (160 microm plate, intended flap diameter 9.0 mm) was used to perform a corneal hinged flap in 35 pig cadaver eyes. Seven blades were reused 5 times each. The flap diameter was measured by planimetry, and the thickness was assessed by ultrasonic pachymetry. Scanning electron microscopy (SEM) of blades and stromal beds was performed.
RESULTS: With single use of the blade, the mean central flap thickness was 145 microm +/- 25 (SD). The vertical/horizontal flap diameter was 9.0 +/- 0.03 mm/8.6 +/- 0.03 mm. No thickness gradient was observed from the incision (138 +/- 31 microm) to the flap hinge (130 +/- 30 microm). If the blade was used more than 2 times, the flap was thinner at the incision (157 +/- 34 microm versus 124 +/- 20 microm; P =.003) and the hinge (143 +/- 24 microm versus 122 +/- 31 microm; P =.04), but the central thickness remained unchanged. With multiple use of the blade, SEM analysis showed increasing cut irregularity, more tissue remnants on the blade surface, and a progression in blade irregularities (up to 9.3 microm).
http://www.fda.gov/cdrh/pdf/p990027s004b.doc
The occurrence rate for the symptoms dryness (22.6% vs. 10.5%, p<0.0001), gritty feeling (6.8% vs 2.6%), fluctuation of vision (14.7% vs. 5.7%, p-value = 0.0005), and variations of vision in dim light (18.1% vs. 27.9%, p<0.0032) were higher at the 6 month visit than at the preoperative visit.
Patient Symptoms at Preop & 6 Months
Patient Symptoms None Mild Moderate to Severe
Preop. 6 Months Preop. 6 Months Preop. 6 Months
Headaches 68.6% (240/350) 84.7% (232/274) 19.7% (69/350) 12.4% (34/274) 11.7% (41/350) 2.9% (8/274)
Redness 75.4% (264/350) 71.9% (197/274) 18.6% (65/350) 20.4% (56/274) 6.0% (21/350) 7.7% (21/274)
Tearing 76.3% (267/350) 88.3% (242/274) 16.3% (57/350) 9.1% (25/274) 7.4% (26/350) 2.6% (7/274)
Gritty feeling 77.4% (271/350) 67.9% (186/274) 19.7% (69/350) 25.5% (70/274) 2.9% (10/350) 6.6% (18/274)
Halos 82.0% (287/350) 73.7% (202/274) 11.1% (39/350) 16.4% (45/274) 6.9% (24/350) 9.9% (27/274)
Double vision 91.7% (321/350) 82.5% (226/274) 5.1% (18/350) 12.0% (33/274) 3.1% (11/350) 5.5% (15/274)
Fluctuations of vision 70.0% (245/350) 38.3% (105/274) 24.3% (85/350) 47.1% (129/274) 5.7% (20/350) 14.6% (40/274)
Variation of vision in normal light 78.9% (276/350) 63.5% (174/274) 16.0% (56/350) 29.2% (80/274) 5.1% (18/350) 7.3% (20/274)
Night driving vision 43.4% (152/350) 59.5% (163/274) 38.0% (133/350) 29.6% (81/274) 18.6% (65/350) 10.9% (30/274)
At 6 months, the symptoms graded as moderate or worse that were reported at an incidence level of more than 1% higher than the baseline incidence level were redness, dryness, gritty feeling, halos, double vision, ghost images, fluctuations of vision, variation of vision in normal light, and variation of vision in dim light.
Am J Ophthalmol. 2006 Mar;141(3):530-536.
Yang CC, Wang IJ, Chang YC, Lin LL, Chen TH. Department of Ophthalmology, Taipei County San-Chung Hospital, Taipei, Taiwan.
PURPOSE: The aim of this study was to develop a predictive model based on preoperative variables for estimating postoperative intraocular pressure (IOP) of those eyes undergoing LASIK surgery, to predict the amount of underestimated IOP after LASIK for myopia and myopic astigmatism.
DESIGN: Pretest-post-test longitudinal study.
METHODS: Both eyes of 193 eligible subjects who underwent LASIK procedures at the Department of Ophthalmology, National Taiwan University Hospital, from July 2000 to December 2002 for myopia and myopic astigmatism were identified to build up the predictive models. IOPs were measured with noncontact air-puff tonometry. Information on age, gender, preoperative central corneal thickness (CCT), preoperative central corneal curvature (CCK), preoperative spherical equivalent refractive error, and ablation depth was collected and applied for predicting postoperative IOP after LASIK based on linear mixed model.
RESULTS: Significant predictors for postoperative IOP after myopic LASIK procedures included age, gender, preoperative IOP, ablation depth, preoperative CCT, and preoperative spherical equivalent refractive errors. The linear mixed model, taking into account these significant preoperative correlates and the correlation of IOPs between both eyes of the same patient, explained 91% of the variation of postoperative IOP.
CONCLUSIONS: A statistical model was developed for predicting the amount of underestimated IOP after LASIK for myopia and myopic astigmatism, which is of clinical importance to uncover ocular hypertension among patients whose information on postoperative IOP immediately after LASIK is not available.
http://www.ophmanagement.com/article.aspx?article=86298
Excerpt: Though the exact cause of TLS is still uncertain, some surgeons believe that the inflammation is caused by necrotic cellular debris, a byproduct of the gas bubbles that are formed to create the flap. Others speculate that the cause may be inflammatory cykotines migrating from the flap interface and sidewall to the perilimbal sclera and iris base.
Flap dimensions created with the IntraLase FS laser
We now know that corneal nerve damage from refractive surgery causes dry eye, and that this nerve damage was found to increase between years 2-3 post LASIK to over 40% loss of corneal nerve density, according to a recent study at the Mayo Clinic:
Dr. Trattler is aware of these findings, but claims that certain palliatives can treat “even the worst dry eye patients after LASIK”:
“We have also shown (in a study I collaborated with Dr. Tseng on) that warm compresses along with other therapies can treat even the worst dry eye patients after LASIK. We took patients from other centers that had failed therapy, and were able to dramatically improve their dry eye state. The study ended 18 months ago, and these patients have done great even since the study end. Part of that is because dry eye is s cycle - so breaking the cycle (with Restasis pre-surgery or other therapies after surgery) can significantly help dry eye after LASIK, and can allow patients to get off Restasis after a number of months.”
Bill Trattler, MD - Miami, FL
Perhaps Dr. Trattler needs to hear from some folks on disability and/or in goggles from their LASIK dry eye.
The asklasikdocs forum is free to join if you care to comment
J Refract Surg. 2006 Mar;22(3):309-12. Related Articles, Links
Ramos-Esteban JC, Servat JJ, Tauber S, Bia F.
Department of Ophthalmology, Yale University School of Medicine, New Haven, Conn, USA.
PURPOSE: To report the history and clinical presentation of a 23-year-old man who developed delayed onset lamellar keratitis in his right eye 2 weeks after uneventful LASIK for correction of myopia. METHODS: Initial clinical presentation suggested an infectious etiology, which led to therapeutic elevation of the LASIK flap and further microbiologic investigation with bacterial cultures.
RESULTS: Bacterial cultures revealed Bacillus megaterium, which was sensitive to all antibiotics against which it was tested. Twenty-four hours after initiating aggressive topical and oral antibiotic therapy, symptomatic relief occurred in the affected eye. The patient's uncorrected final visual acuity at 1-year follow-up was 20/15 in the right eye, and the stromal bed developed a faint peripheral non-visually significant scar. CONCLUSIONS: This case is an unusual presentation and course for microbial keratitis following LASIK, which occurred despite aseptic technique and fluoroquinolone antibiotic prophylaxis. Following refractive surgery one should be prepared to culture the lamellar interface in cases of suspected microbial keratitis and begin aggressive antibiotic therapy.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16386969&query_hl=7&itool=pubmed_docsum
American Journal of Ophthalmology Volume 141, Issue 1 , January 2006, Page 1 Kuang-Mon Ashley Tuan OD, PhDa, Dimitri Chernyak PhDa and Sandy T. Feldman MD, MSb, ,
a) VISX Inc, Santa Clara, California b) ClearView Eye and Laser Medical Center, San Diego, California.
Purpose: To evaluate the accuracy of the diagnostic capabilities of optical metrics generated from wavefront measurements in relationship to post–laser-assisted in situ keratomileusis (LASIK) visual complaints as expressed and drawn by patients.
Design: Retrospective analysis and observational case series.
Methods: Patient wavefront data from an investigational device exemption study for wavefront-guided ablations were used to derive normative modulation transfer function (MTF), encircled energy (EE), and Strehl ratio. These optical metrics and their point-spread functions (PSF) were compared with data from five postoperative patients with night vision complaints. Patients were asked to draw their symptoms, which were elicited by testing with a Fenthoff muscle light, while using their best-corrected distance vision.
Results: The MTF, EE, and Strehl ratio of most patients were markedly different from those of the averages of 208 normal myopic eyes before and after LASIK surgery. The spatial extent of the PSF correlated positively with the severity of the visual complaints. Wavefront-derived PSFs were markedly similar to the patients’ drawings.
Conclusions: The results of this study demonstrate the diagnostic capability of the wavefront system in predicting visual symptoms and complaints of patients with high-order aberrations. Objective visual metrics from patients with night vision complaints were different from those of normal myopic eyes that had undergone LASIK procedures.
Excerpts: If the human eye were a perfect optical system, the appearance of a point source of light would be limited only by diffraction effects, and the source would appear as a single point to the observer. In addition to spherocylindrical components, the optical system of the human eye generates other complex optical aberrations, which contribute to the distortion of retinal images and determine the quality of the image formed on the retina. The optical imperfections of the eye cause rays of light traveling from a point source through the eye’s optics to intercept the retina at different locations, thereby blurring the appearance of the point. The distorted appearance of the point on the retina is called a point-spread function (PSF).
The recent development of wavefront aberrometers for use in ophthalmology has given clinicians an objective measurement method for optical aberrations other than sphere and cylinder. The wavefront maps generated by such devices represent deviations from the ideal diffraction-limited optical systems and enable the physician to precisely diagnose visual impairment. In addition to guiding customized refractive surgery, wavefront sensors can be used to evaluate the source of visual complaints. The appearance of the PSF can be computed directly from the wavefront measurement and corroborated by the patient with a simple drawing.
In recent years, much emphasis has been placed on the use of PSF and PSF-based metrics to objectively evaluate the quality of vision (Gross E, Wavefront Congress 2004, Abstract).3 and 4 Whereas the wavefront map (which is analytically defined by methods that include the Zernike coefficients) describes the aberrations in the pupillary plane, the PSF describes aberrations in the retinal plane. Retina-based descriptions of aberrations have been shown to correlate strongly with subjective visual metrics, such as visual acuity and contrast sensitivity.
In addition to correlating with subjective measures of visual performance, the PSFs are valuable tools for understanding visual symptoms, such as ghost images, which occur with multiple peaks of the PSF, or halos and starbursts, which may also be inferred from the appearance of the PSF. The purpose of this study is to determine whether quantitative analysis of PSFs is helpful to the clinician’s understanding of nighttime visual complaints.
Methods: This study was a retrospective analysis and observational case series. Two groups of patients were included in this study. The first group of eyes were nonsymptomatic and were used to establish normative values. Data from this group were gathered from 208 eyes from the six clinical sites in the United States that participated in the Institutional Review Board–approved investigative device exemption study for the CustomVue wavefront-guided laser vision correction procedure (VISX Inc, Santa Clara, California, USA). The second group of patients, all of whom had night complaints after laser-assisted in situ keratomileusis (LASIK), was recruited from the practice of ClearView Eye Center, San Diego, California, USA. The purpose of this part of the study was to see whether sketches of the point source of light made by patients with night vision complaints would be reasonably similar to the polychromatic PSF plot created by the WaveScan aberrometer, and to determine whether their optical metrics were different from the normal population. Inclusion criteria included a complaint of glare, halo, starburst at night, or a poorer quality of vision. Patients were also required to be willing to sketch their symptoms.
WaveScan version 3.5 software was used to convert the wavefront data into PSF. The PSF was computed by using multiple wavelengths to accurately simulate the appearance of white light and to account for chromatic aberrations of the eye. The Stiles-Crawford effect of the first kind, which depicts the probability of photon absorption by photoreceptors as a function of ray position from the pupil center, was also taken into account. Additionally, absorption spectra of the three retinal photoreceptor types were used to correctly weight different wavelengths in the PSF computations. Finally, spacing of the retinal receptor mosaic was used to determine the maximum spatial frequency that is used in the rendition of the PSF.
An important issue in assessing retinal image quality is a realistic computation of the PSF. The above method enables the instrument to create realistic renditions of the appearance of a white light point source on the image plane, which is the polychromatic PSF. An optical system with little aberration will generate a compact and high-intensity point source on the image plane. Therefore, the brain would be expected to perceive sharp images and resolve small details. A highly aberrated eye will form a PSF that spreads out and has lower contrast within the retinal plane. In this case, the brain would perceive a dim and blurry image resulting in low resolution and poor visual performance.
To effectively compare the visual impact of different PSFs, it is necessary to quantify PSF or PSF plots. To date, there is no consensus in the vision science community as to a standardized method for quantifying the visual impact of measured wavefront aberration. However, Strehl ratio, encircled energy (EE), and modulation transfer function (MTF) are the commonly used optical metrics believed to provide useful information on perceptual image quality and therefore predict visual performance.3, 4, 7 and 8 For this study, the PSF was broken down into two parts for visual evaluation: circle of blur; and the length of the vertical and horizontal strikes from the center. Optical metrics such as Strehl ratio, EE, and MTF were derived from the PSF8 with the intention of quantifying the visual impact of the PSF.
Strehl ratio is defined as the ratio of the peak intensities of the aberrated PSF and the diffraction-limited PSF. EE is the two-dimensional integral of the PSF. EE represents the proportion within a given radius of the image center and the total energy from a point source. EE was calculated at 1, 3, 5, 8, and 10 min of arc. MTF is the module of Fourier transform of the PSF. MTF represents contrast information, and it varies with spatial frequencies. MTF was calculated from 3 cycles per degree (cpd) to 30 cpd for this study. An MTF of 1 indicates that 100% contrast was maintained after the light passed through the optical system. The normative value of the optical metrics described above was used for comparison with patients with postoperative visual symptoms. Lower-order wavefront information was deleted from the calculation to remove optical degradation arising from refractive error.
Results: All patients were healthy men ranging in age from 31 to 43. Patient demographic information is listed in Table 1. Their drawings and corresponding PSFs are presented in Figure 1. The postoperative follow-up period ranged from 6 months to 3 years. Postoperative uncorrected vision ranged from 20/30 to 20/20 and was correctable in each eye to 20/20 or better. However, patients reported visual symptoms at follow-up visits. Unfortunately, not all of the patients’ preoperative visual information was available.
Discussion: It is well known that patients with nighttime vision complaints may nevertheless have excellent uncorrected acuity. The clinician does not have many clinical tests outside of questionnaires to assess the extent of symptoms such as glare, halo, and starburst. Additionally, literature on clinical methods with which to demonstrate night complaints or quantify the visual disturbance is scarce. In this study, we have demonstrated that optical metrics derived from polychromatic PSF are a reliable quantitative method for the validation of night vision complaints.
The PSF diagram represents the appearance of one small spot of light after it passes through an optical system. The authors found the WaveScan-generated PSF to be consistently similar to the subjective visual experience of the study subjects despite differences in the artistic abilities of the patients. The polychromatic PSF plots derived from the wavefront measurements bear marked similarities to the drawings of the patients. The PSF plots show diffraction effects and some subthreshold light. Diffraction-based spatial frequencies are missing from drawings because they are not perceived. Additionally, the spacing of the photoreceptors limits visual acuity and spatial resolution of the retina. Occupation, personality, and level of detail orientation also appear to help determine the way patients perceive their visual quality. Therefore, patients with similar PSFs can have different reactions to their quality of vision. Nevertheless, the similarity between the PSF maps of subjects who have visual symptoms and their drawings are evident.
Optical metrics generated from the PSF were used to create a quantitative description of a PSF diagram. Optical metrics apply summations from different areas and orientations, and the result is a directionless quantitative number. The authors chose to use three metrics: Strehl ratio, EE, which signifies the intensity of the brightness of the image, and MTF, which represents contrast information. The study patients were compared with the normative values of EE and MTF generated from a cohort that had never undergone refractive surgery. Most optical metrics in the study patients were significantly worse than the normative values.
Lowered EE and MTF in the left eye of patient 4 are marginally significant, and there is a high amount of negative spherical aberration. The PSF maps are more vertically distributed. After averaging in all directions, the effect on overall optical metrics was reduced, which may explain why patient 4 had both positive visual symptoms but was within the normal limits of EE and MTF. However, patient 4’s PSF map shows an asymmetrical pattern in which the vertical dimension spreads outside the normal range. This extensive vertical spread of light accounts for the patient’s visual symptoms and correlates with his drawings. After examining the visual functions of seven patients who underwent LASIK procedures, Holladay and coauthors hypothesized that corneas with an oblate shape or positive spherical aberration contributed to the decrease of visual functions. In our study patients, patients 1 and 4 had significant negative spherical aberration or prolate cornea (−0.41 μm and −0.25 μm, respectively) but also had visual symptoms. Spherical aberration was one of the few “abnormal” optical metrics for patient 4. This observation suggests that negative spherical aberration is not necessarily associated with visual satisfaction. On the contrary, when spherical aberration is present in sufficient magnitude, it could cause visual dissatisfaction.
In our study patients, some patients’ uncorrected visual acuity nevertheless experienced persistent visual symptoms, even with their best-corrected vision.
Polychromatic PSF plots generated from VISX’s polychromatic wavefront algorithms showed high correlation with the patients’ subjective visual experiences.
In conclusion, this study shows that wavefront systems are capable of predicting nighttime visual symptoms and complaints of patients whose visual acuities are otherwise good. Polychromatic PSF and the optical metrics derived from it are valuable diagnostic tools for predicting quality of vision and for evaluating the optical quality of an eye.
J Refract Surg. 2006 Jan-Feb;22(1):48-53. Hiatt JA, Grant CN, Wachler BS.
Boxer Wachler Vision Institute, 465 N Roxbury Dr, Ste 902, Beverly Hills, CA 90210, USA.
PURPOSE: To report the results of complex wavefront-guided LASIK retreatments.
METHODS: Twenty eyes (15 patients) with histories of conventional LASIK surgery and significant visual complaints of glare and halos due to higher order aberrations were treated. Wavefront-guided retreatments were performed with the LADARVision CustomCornea system (Alcon, Ft Worth, Tex). Pre- and postoperative topographies, wavefront measurements, and subjective reports were analyzed.
RESULTS: Postoperatively, patients had an expanded optical zone, many with improved centration. Lower and higher order aberrations decreased following wavefront-guided ablation. Mean higher order root-mean-square decreased from 1.01 +/- 0.25 microm preoperatively to 0.84 +/- 0.23 microm postoperatively. Mean coma decreased from 0.59 +/- 0.26 microm to 0.43 +/- 0.21 microm. Mean spherical aberration decreased from 0.66 +/- 0.25 microm to 0.54 +/- 0.27 microm. Subjective reports of glare and halo symptoms improved in all patients.
CONCLUSIONS: CustomCornea wavefront-guided treatments are effective in reducing lower and higher order aberrations, expanding optical zones, and improving subjective reports of adverse aberration sequelae such as glare and halos.
1: J Refract Surg. 2003 Mar-Apr;19(2):113-23. Flanagan GW, Binder PS. Gordon Binder Vision Institute, San Diego, CA, USA. PURPOSE: To determine the factor(s) that influence the dimensions and predictability of the LASIK corneal flap with the Automated Corneal Shaper (ACS) or the Summit Krumeich Barraquer microkeratome (SKBM). METHODS: We performed a retrospective, comparative interventional case study of 4,428 eyes. Flap dimensions were measured using subtraction ultrasonic pachymetry during LASIK with one of two microkeratomes. RESULTS: Mean preoperative corneal thickness for all eyes was 555 +/- 35 microm. Corneal curvature and refractive astigmatism were inversely related to preoperative corneal thickness (P<.001). With an attempted flap thickness of 160 microm, the ACS flap thickness averaged 119.8 +/- 22.9 microm; SKBM flaps averaged 160.9 +/- 24.1 microm (P<.001). The coefficient of variation for central pachymetry compared to flap thickness was 6.4% vs. 22.1%. Flap thickness at enhancement was 10 to 17 microm thicker than at primary surgery. An increase in flap thickness was associated with thicker preoperative pachymetry (P<.001) and younger age for both instruments (P<.001) whereas increasing flap thickness was related to flatter preoperative mean keratometry for the ACS (P<.001) and steeper mean keratometry for the SKBM (P=.005). Less preoperative hyperopia or more myopia was related to an increase in flap thickness only for the SKBM (P<.001). CONCLUSIONS: Flap thickness varies significantly depending on the microkeratome used. Factors that influence flap thickness are primarily corneal thickness, patient age, preoperative keratometry, preoperative refraction including astigmatism, and corneal diameter. By understanding the factors that affect flap thickness, one can select a microkeratome system to allow maximum refractive correction while minimizing the risk of ectasia.
http://www.ncbi.nlm.nih.gov/entrez/...st_uids=9932992
American Journal of Ophthalmology
Volume 127, Issue 1 , January 1999, Pages 1-7
Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis.
Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA.
Department of Ophthalmology, University of Tokyo School of Medicine, Japan. oshika-tky@umin.ac.jp
Excerpt: Before surgery, simulated pupillary dilation from 3 to 7 mm caused a five- to six-fold increase in the total aberrations. After surgery, the same dilation resulted in a 25- to 32-fold increase in the photorefractive keratectomy group and a 28- to 46-fold increase in the laser in situ keratomileusis group.
J Cataract Refract Surg. 2005 Nov;31(11):2216-20.
Hamill MB, Quayle WH.
From the Cullen Eye Institute, Baylor College of Medicine, Department of Ophthalmology (Hamill), and UTMB Galveston Houston Eye Associates (Quayle), Houston, Texas, USA.
This report illustrates the surgical approach to and results of a complex iris reconstruction. The presentation and long-term visual and architectural results (follow-up of 4 years) of the repair of a severe anterior segment injury after entry into the anterior chamber by a microkeratome during laser in situ keratomileusis is described. The techniques used in the repair are described in detail, and a historical review of iris repair techniques is presented.
2005 Jan;24(1):92-102.
Pathologic findings in postmortem corneas after successful laser in situ keratomileusis.
Kramer TR, Chuckpaiwong V, Dawson DG, L'Hernault N, Grossniklaus HE, Edelhauser HF.
Emory Eye Center, Emory University, Atlanta, GA 30322, USA. Theresa_Kramer@emoryhealthcare.org
PURPOSE: To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK).
METHODS: Corneas from 48 eyes of 25 postmortem patients were processed for histology and transmission electron microscopy (TEM). The 25 patients had LASIK between 3 months and 7 years prior to death. Evaluation of all 5 layers of the cornea and the LASIK flap interface region was done using routine histology, periodic acid-Schiff (PAS)-stained specimens, toluidine blue-stained thick sections, and TEM.
RESULTS: In patients for whom visual acuity was known, the first postoperative day uncorrected visual acuity was 20/15 to 20/30. In patients for whom clinical records were available, the postoperative corneal topography was normal and clinical examination showed a semicircular ring of haze at the wound margin of the LASIK flap. Histologically, the LASIK flap measured, on average, 142.7 microm (range, 100-200). A spectrum of abnormal histopathologic and ultrastructural findings was present in all corneas. Findings at the flap surface included elongated basal epithelial cells, epithelial hyperplasia, thickening and undulations of the epithelial basement membrane (EBM), and undulations of Bowman's layer. Findings in or adjacent to the wound included collagen lamellar disarray; activated keratocytes; quiescent keratocytes with small vacuoles; epithelial ingrowth; eosinophilic deposits; PAS-positive, electron-dense granular material interspersed with randomly ordered collagen fibrils; increased spacing between collagen fibrils; and widely spaced banded collagen. There was no observable correlation between postoperative intervals and the severity or type of pathologic change except for the accumulation the electron-dense granular material.
CONCLUSIONS: Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.
Read more
A recent study on the effects of the excimer laser on corneal tissue: Joshua Ben-num (Tzriffin, Israel)
Photorefractive Keractectomy and Laser in situ Keratomileusis: A Word From the Devil's Advocate.
Archives of Ophthalmol. Vol.118, Dec.2000, p.1706-1707.
At a time when there has been a significant improvement in the technology of treatment of refractive errors by laser in-situ keratomileusis (LASIK), this author has issued a very timely warning both to patients undergoing the procedure and to the people performing LASIK.
The procedure involves a laser beam at 193nm that evaporates part of the cornea, breaking cells and molecules to create the smooth corneal surface necessary for best optical results.
The creation of free radicals, is an inseparable part of the cornea reshaping process.
Both photorefractive keratectomy (PRK) and LASIK are known to cause keratocyte apoptosis in the cornea of laboratory animals and hence, though there is no short-term damage, long-term damage must be considered.
These procedures are also known to have caused biochemical and ultrastructural modifications in the lens, both of which are markers of cataractogenesis. The vitreous base, located just posterior to the lens may be affected by the same process that affects the cornea, anterior chamber and the lens. Free radicals damage the vitreous collagen, leading to vitreous liquefaction. They have also been shown to promote tumours.
PRK might initiate a cascade of events leading to slowly developing abnormalities of the cornea, lens, vitreous retina and choroid.
On one hand there is a marked increase in the popularity of LASIK promulgated by massive advertisement. Hence there is an urgent need for intensive research into the potential threats to ocular function caused by LASIK which may occur in patients decades after the initial procedure, slowly but almost surely.
Fatal Focus, a novel by Jonathan Maxx
Am J Ophthalmol. 2005 Jun;139(6):1137-9.
McLeod SD, Mather R, Hwang DG, Margolis TP. Francis I. Proctor Foundation and the Department of Ophthalmology, University of California-San Francisco, 10 Kirkham Street, San Francisco, CA 94143, USA. smcleod@itsa.ucsf.edu
PURPOSE: To report two cases of corneal pathology associated with anterior uveitis after laser in situ keratomileusis (LASIK).
DESIGN: Observational case report.
METHODS: A 47-year-old man and a 50-year-old woman who experienced vision loss and corneal changes associated with acute anterior uveitis after LASIK were examined.
RESULTS: The 47-year-old man, who had undergone LASIK for low myopia developed an interlamellar fluid pocket at the level of the flap interface, whereas the 50-year-old woman, who underwent LASIK for hyperopia, developed marked flap edema without interface fluid collection.
CONCLUSIONS: These two cases demonstrated acute corneal fluid accumulation associated with episodes of acute anterior uveitis in eyes that had undergone LASIK. Uveitis should be considered a risk factor for vision threatening corneal complications after LASIK.
The Promise of Refractive Surgery: A Promise Not Kept
An Insiders Journal on the Evolution and Misinformation of Refractive Surgery
Dedicated to:
And the thousands of others whose quality of life has suffered greatly as a result of
believing the professionally communicated promise of refractive surgery
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15519085&query_hl=71: J Cataract Refract Surg. 2004 Nov;30(11):2336-43. Macsai MS, Stubbe K, Beck AP, Ravage ZB. Division of Ophthalmology, Evanston Northwestern Healthcare, Glenview, IL 60025, USA. mmacsai@enh.org PURPOSE: To evaluate the effect of expanding the treatment zone of the Nidek EC-5000 laser on postoperative visual acuity as well as night glare and halos after laser in situ keratomileusis (LASIK) using 4 ablation zone diameters.
SETTING: Division of Ophthalmology, Evanston Northwestern Healthcare and Northwestern University Medical School, Glenview, Illinois, USA. METHODS: This prospective study comprised 301 eyes of 154 consecutive patients who had LASIK in 1 or both eyes using the Nidek EC-5000 laser by 1 surgeon with experience in keratomileusis and excimer laser refractive surgery. A 6.5 mm optical zone was used with a transition zone 1.0 mm larger than the pupil under scotopic conditions (7.5, 8.0, 8.5, or 9.0 mm). Targeted correction was calculated according to a customized clinical nomogram. All patients were queried about glare and halos preoperatively and 3 months postoperatively using a questionnaire assigning numeric values to the degree of perceived visual disturbance (0 = no glare or halos, 1 = minimal, 2 = moderate, 3 = severe).
RESULTS: The baseline uncorrected visual acuity (UCVA) was 20/200 or worse in 293 eyes. The baseline best spectacle-corrected visual acuity was 20/20 or better. The mean preoperative refractive sphere was -6.33 diopters (D) +/- 2.80 (SD) (range -1.00 to -16.25 D) and the mean preoperative refractive cylinder, 0.86 +/- 0.83 D (range 0 to +3.25 D). Three months postoperatively, 78% of eyes had a UCVA of 20/20 and 99%, of 20/40 or better. Preoperatively, 94 eyes (31%) had glare and halos. At 3 months, glare, halos, or both were present in 19 eyes of 11 patients (6.3%) (P<.0001); in 14 eyes, patients reported less severe glare and halos postoperatively than preoperatively.
CONCLUSIONS: The use of a peripheral transition zone 1.0 mm larger than the pupil under scotopic conditions resulted in a low incidence of glare and halos postoperatively and did not adversely affect visual acuity. There was no increase in postoperative complications including corneal ectasia.
Cornea. 23, 8 Supplement 1:S59-S64, November 2004. Kamiya, Kazutaka MD *; Miyata, Kazunori MD +; Tokunaga, Tadatoshi COT +; Kiuchi, Takahiro MD ++; Hiraoka, Takahiro MD ++; Oshika, Tetsuro MD ++ Abstract: Purpose: To review the time course of corneal anteroposterior shift and refractive stability after myopic excimer laser keratorefractive surgery. Methods: We examined 65 eyes undergoing photorefractive keratectomy (PRK) and 45 eyes undergoing laser in situ keratomileusis (LASIK). Corneal elevation maps and pachymetry were obtained by scanning-slit corneal topography before; 1 week; and 1, 3, 6, and 12 months after surgery. Results: Both PRK and LASIK induced significant forward shifts of the cornea. Corneal forward shift was progressive up to 6 months after PRK, but no progression was seen after LASIK. Progressive thinning and expansion of the cornea were not observed after either procedure. The amount of corneal forward shift showed a significant negative correlation with preoperative corneal thickness (r = -0.586; P < 0.01) and a significant positive correlation with the amount of myopic correction (r = 0.504; P < 0.01). A significant correlation was found between the amount of forward shift and the degree of myopic regression after surgery (r = -0.347; P < 0.05). Conclusion: Myopic PRK and LASIK induce significant forward shifts of the cornea, which are not true corneal ectasia. Eyes with thinner corneas and higher myopia requiring greater ablation are more predisposed to anterior protrusion of the cornea. Corneal forward shift was progressive up to 6 months after PRK but not progressive after LASIK. Forward shift of the cornea can be one of the factors responsible for myopic regression after surgery.
Invest Ophthalmol Vis Sci. 2004 Nov;45(11):3991-6.
Corneal reinnervation after LASIK: prospective 3-year longitudinal study.
Calvillo MP, McLaren JW, Hodge DO, Bourne WM.
Department of Ophthalmology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
PURPOSE: To measure the return of innervation to the cornea during 3 years after LASIK.
METHODS: Seventeen corneas of 11 patients who had undergone LASIK to correct myopia from -2.0 D to -11.0 D were examined by confocal microscopy before surgery, and at 1, 3, 6, 12, 24, and 36 months after surgery. In all available scans, the number of nerve fiber bundles and their density (visible length of nerve per frame area), orientation (mean angle), and depth in the cornea were measured.
RESULTS: The number and density of subbasal nerves decreased >90% in the first month after LASIK. By 6 months these nerves began to recover, and by 2 years they reached densities not significantly different from those before LASIK. Between 2 and 3 years they decreased again, so that at 3 years the numbers remained <60% of the pre-LASIK numbers (P <0.001). In the stromal flap most nerve fiber bundles were also lost after LASIK, and these began recovering by the third month, but by the third year they did not reach their original numbers (P <0.001). In the stromal bed (posterior to the LASIK flap interface), there were no significant changes in nerve number or density. As the subbasal nerves returned, their mean orientation did not change from the predominantly vertical orientation before LASIK. Nerve orientation in the stromal flap and the stromal bed also did not change.
CONCLUSIONS: Both subbasal and stromal corneal nerves in LASIK f
