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PubMed2005

Comparison of corneal higher-order aberrations induced by myopic and hyperopic LASIK.

OBJECTIVE: To compare the change in anterior corneal higher-order (third- to fifth-order) aberrations (HOAs) induced by myopic and hyperopic LASIK. DESIGN: Retrospective comparative case series. PARTICIPANTS: One hundred eyes (50 myopes and 50 hyperopes) of 59 patients were included. The mean preoperative spherical equivalent (SE) was -4.22+/-1.78 diopters (D; range, -1.25 to -8.00 D) in the myopic group (group A) and +2.72+/-1.25 D (range, +0.25 to +5.00 D) in the hyperopic group (group B). INTERVENTION: LASIK was performed using a conventional spherocylindrical laser algorithm (Planoscan V2.9992, Bausch & Lomb/Technolas, Munich, Germany). Optical zone diameter was 6.70+/-0.32 mm (range, 6-7 mm) in group A and 6.59+/-0.19 mm (range, 6.5 to 7 mm) in group B. Third to fifth corneal HOA were computed for a pupil diameter of 6 mm from corneal topographic examinations before and 1 month after surgery. MAIN OUTCOME MEASURES: Change in corneal HOAs, derived from corneal topography. RESULTS: Total HOA root mean square (RMS) changed in group A by 0.167+/-0.180 microm (factor 1.53) and in group B by 0.341+/-0.341 microm (factor 1.89). The mean induction of coma RMS was significantly different in both groups (myopes, 0.092+/-0.195 microm; hyperopes, 0.252+/-0.305 microm; P<0.05). For spherical aberration (Z 4,0), the myopic group showed a significant increase (0.130+/-0.120 microm; factor 1.6; P<0.001), whereas the hyperopic group showed a significant decrease (-0.317+/-0.158 microm; factor 0.76; P<0.001). Fifth-order aberrations showed an increase in both groups, which was higher in group B (0.069+/-0.120 microm; factor 2.46) than in group A (0.005+/-0.065 microm; factor 1.49). CONCLUSIONS: Myopic and hyperopic LASIK had different patterns of HOA induction. Myopic LASIK induced positive spherical aberrations and positive secondary astigmatism, whereas hyperopic LASIK induced negative spherical aberrations and negative secondary astigmatism. Hyperopic LASIK induced more third- and fifth-order comalike aberrations than myopic LASIK.

Adult↗
PubMed2005

Conductive keratoplasty to treat complications of LASIK and photorefractive keratectomy.

PURPOSE: To assess the outcomes of conductive keratoplasty (CK) for patients with complications related to LASIK or photorefractive keratectomy (PRK). DESIGN: Retrospective, noncomparative, interventional case series. PARTICIPANTS: Sixteen eyes of 15 patients were treated using CK after complications of initial LASIK or PRK surgeries. Five cases are described in detail. INTERVENTION: Rehabilitative CK was performed. MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), refractive error, keratometry, topography analysis, and a subjective assessment of visual quality. RESULTS: After CK treatment, there was a mean improvement in UCVA of 2 lines; 1 eye lost >1 line of UCVA. Best-corrected visual acuity improved or remained the same in 12 of 15 eyes; no eyes lost >1 line of BSCVA. There was a mean reduction in astigmatism of 54%. Videokeratography generally demonstrated improved quality of the corneal optical surface, and patients reported a reduction in optical symptoms such as glare and halo. CONCLUSIONS: Conductive keratoplasty may give improved corneal optics and vision in patients with complications of LASIK or PRK. This application of CK offers an alternative in cases in which further flap manipulation or laser treatments are contraindicated.

Adult↗
PubMed2005

Long-term outcomes of photorefractive keratectomy for anisometropic amblyopia in children.

PURPOSE: To evaluate the long-term visual acuity (VA) and refractive error responses to excimer laser photorefractive keratectomy (PRK) for treatment of anisometropic amblyopia in children. DESIGN: Prospective interventional case-control study. PARTICIPANTS: Eleven children, 2 to 11 years old, with anisometropic amblyopia who were noncompliant with conventional therapy with glasses or contact lenses and occlusion therapy were treated with PRK. A cohort derived retrospectively of 13 compliant and 10 noncompliant children with refractive errors similar to those of the PRK group who were treated with traditional anisometropic amblyopia therapy served as control groups. INTERVENTION: Photorefractive keratectomy for the eye with the higher refractive error. MAIN OUTCOME MEASURES: (1) Refractive error reduction and stability in the treated eye, (2) cycloplegic refraction, (3) VA, (4) stereoacuity, and (5) corneal haze up to 3 years after PRK. Compliant and noncompliant children with anisometropia amblyopia were analyzed as controls for refractive error and VA. RESULTS: Preoperative refractive errors were -13.70 diopters (D) (+/-3.77) for the myopic group and +4.75 D (+/-0.50) for the hyperopic group. Mean postoperative refractive errors at last follow-up (mean, 31 months) were -3.55 D (+/-2.2.5) and +1.41 D (+/-1.07) for the myopic and hyperopic groups, respectively. At last follow-up, cycloplegic refractions in 4 (50%) of 8 myopes and all hyperopes (100%) were within 3 D of that of the fellow eye. Five (63%) of 8 myopic children achieved a refraction within 2 D of the target refraction. Two (67%) of 3 hyperopic patients maintained their refractions within 2 D of the target. Refractive regressions (from 1 year after surgery to last follow-up) were 0.50+/-1.41 D (myopes) and 0.60+/-0.57 D (hyperopes). Seven children (77%) were able to perform psychophysical VA testing preoperatively and postoperatively. Five (71%) of the 7 children had uncorrected VA improvement of at least 2 lines, and 4 (57%) of 7 had best spectacle-corrected VA improvement of at least 2 lines, with 1 improving 7 lines. Five (55%) of 9 children had improvement of their stereoacuity at last follow-up. Subepithelial corneal haze remained negligible. The mean final VA of the PRK group was significantly better than that of the noncompliant control group (P = 0.003). The mean final refractive error for both myopic and hyperopic groups was also significantly better that that of the control groups (P = 0.007 and P<0.0001, respectively). CONCLUSIONS: Photorefractive keratectomy for severe anisometropic amblyopia in children resulted in long-term stable reduction in refractive error and improvement in VA and stereopsis, with negligible persistent corneal haze.

Amblyopia↗
PubMed2006

Infectious keratitis after photorefractive keratectomy in the United States army and navy.

PURPOSE: To review the incidence, culture results, clinical course, management, and visual outcomes of infectious keratitis after photorefractive keratectomy (PRK) at 6 Army and Navy refractive surgery centers. DESIGN: Retrospective study. PARTICIPANTS: Twelve thousand six hundred sixty-eight Navy and Army sailors and service members. METHODS: Army and Navy refractive surgery data banks were searched for cases of infectious keratitis. A retrospective chart review and query of the surgeons involved in the care of those patients thus identified provided data regarding preoperative preparation, perioperative medications, treatment, culture results, clinical course, and final visual acuity. RESULTS: Between January 1995 and May 2004, we performed a total of 25337 PRK procedures at the 6 institutions. Culture proven or clinically suspected infectious keratitis developed in 5 eyes of 5 patients. All patients received topical antibiotics perioperatively. All cases presented 2 to 7 days postoperatively. Cultures from 4 cases grew Staphylococcus, including 2 methicillin-resistant S. aureus (MRSA). One case of presumed infectious keratitis was culture negative. There were no reported cases of mycobacterial or fungal keratitis. In addition, we identified 26 eyes with corneal infiltrates in the first postoperative week that were felt to be sterile, and which resolved upon removal of the bandage contact lens and increasing antibiotic coverage. CONCLUSIONS: Infectious keratitis is a rare but potentially vision-threatening complication after PRK. It is often caused by gram-positive organisms, including MRSA. Early diagnosis, appropriate laboratory testing, and aggressive antimicrobial therapy can result in good outcomes.

Anti-Bacterial Agents↗
PubMed2006

Cataractous changes due to posterior chamber flattening with a posterior chamber phakic intraocular lens secondary to the administration of pilocarpine.

OBJECTIVE: To present the first reported case of cataract formation as a consequence of instillation of pilocarpine in an eye with a posterior chamber phakic intraocular lens (IOL). DESIGN: Interventional case report. INTERVENTION: A 46-year-old man received a hyperopic implantable collamer lens (ICL) bilaterally. MAIN OUTCOME MEASURES: Determination of best-corrected visual acuity (BCVA); contrast sensitivity testing with and without glare; and intraocular pressure (IOP), specular endothelial cell, and slit-lamp examinations were performed serially. In addition, the distance between the ICL and crystalline lens was measured with optical coherence tomography. RESULTS: Both eyes underwent uneventful ICL implantation for the correction of a manifest spherical equivalent of +7 diopters (D) in the right eye and +7.1 D in the left eye. The left eye was followed for 2 years without developing complications. The right eye, however, showed on the first postoperative day a fleckenlike opacification on the anterior pole of the crystalline lens after instillation on the operative day of 2% pilocarpine in an attempt to accelerate recovery from unwanted pupil dilation causing patient complaints of glare disability after surgery. Optical coherence tomography demonstrated complete contact of the ICL with the natural lens 24 hours postoperatively. Serial IOP measurements were always within the normal limits. The instillation of 1% cyclopentolate resulted in an increase in the ICL vault that measured 132 mum 24 hours later. Three days after the completion of a 3-day course of topical 1% cyclopentolate, the opacification was less dense and demarcated, and a 124-mum vault was measured. Three months postoperatively, the cataract was associated with a 3-line loss of BCVA and considerable degradation of the contrast sensitivity, especially at higher spatial frequencies and with a glare source, and corneal endothelial cell changes were within normal limits. One year after ICL implantation, the right eye had to undergo phacoemulsification and IOL implantation, which were uneventful. CONCLUSIONS: Posterior chamber flattening with resulting crystalline lens opacification can occur immediately after the instillation of pilocarpine in an eye with a hyperopic ICL. Therefore, caution should be taken with the administration of cholinergic agonists such as pilocarpine in patients with phakic IOLs, at least if they are hyperopic ICLs.

Cataract↗
PubMed2004

Treatment of astigmatism-related amblyopia in 3- to 5-year-old children.

Best-corrected acuity was measured for vertical and horizontal gratings and for Lea Symbols recognition acuity in 3- to 5-year-old children with high astigmatism and in non-astigmatic children. There was significant amblyopia among astigmatic children at baseline. There was no evidence that eyeglass correction of astigmatism resulted in a reduction in amblyopia over a 4-month average treatment duration (although vision in astigmatic children was significantly improved immediately upon eyeglass correction, indicating that eyeglass correction did provide a visual benefit). Treatment outcome results are discussed in terms of both methodological issues and theoretical implications.

Amblyopia↗
PubMed2005

Influence of age on peripheral refraction.

To investigate how age affects peripheral refraction we measured objective peripheral refraction for 55 young subjects (24+/-4 years) and 41 older subjects (59+/-3 years) out to 35 degrees eccentricity in temporal and nasal visual fields. Subjects were compared in 1D subgroups based on central spherical equivalent refractions (low hypermetropes +0.54 D to +1.51 D, emmetropes +0.50 D to -0.49 D, low myopes -0.50 D to -1.49 D, moderate myopes -1.50 D to -2.58 D). Overall, young and older subjects with similar refractive corrections had similar peripheral refraction components. Both age groups showed relative hypermetropic shifts in the peripheral fields as myopia increased and also decreases in peripheral astigmatism J180 as myopia increased. J45 varied little across the visual field with linear relationships occurring between J45 and visual field angle for all but one subgroup (older emmetropes). Peripheral refraction in emmetropes to moderate myopes is relatively unaffected by age for healthy eyes of similar refractive errors.

Adult↗
PubMed2005

Effects of interchanging hyperopic defocus and form deprivation stimuli in normal and optic nerve-sectioned chicks.

To test the hypothesis that the same mechanisms mediate form deprivation and lens-induced myopia, the ocular growth responses of chicks alternately exposed to lenses and diffusers at regular intervals (3h) were compared to those of chicks exposed to either negative lenses or diffusers alone. In total, there were four experiments: (1) -15 D lenses and/or diffusers on normal birds, (2) -15 D lenses and/or diffusers on optic nerve-sectioned (ONS) birds, (3) -5/-10/-15 D lenses (sequentially applied) and/or diffusers on normal birds and (4) -5/-10/-15 D lenses and/or diffusers on ONS birds. All treatments were monocular. In all experiments, optical axial lengths (cornea-to-retina distances) in treated eyes were greater than in fellow eyes, irrespective of the optical device (diffuser, lens or switch), lens power (fixed or incremented) and optic nerve condition (intact or severed). In normal chicks, optical axial length responses in the switch group were significantly reduced relative to those of the diffuser but not to those of the -15 D lens group. For both groups of ONS birds, diffusers exaggerated the optical axial length changes. For all groups, the responses to the switch and lens groups were most similar. These results together suggest that the mechanisms mediating form deprivation- and lens-induced myopia are different.

Animals↗
PubMed2000

Laser in situ keratomileusis flap margin: wound healing and complications imaged by in vivo confocal microscopy.

PURPOSE: To examine the healing response of laser in situ keratomileusis flap margin in vivo. METHODS: Forty-three eyes of 43 patients who had undergone myopic (n = 39) or hyperopic (n = 4) laser in situ keratomileusis were examined once after surgery. The flap margin was imaged by in vivo confocal microscopy at various depths, and the wound healing response, flap alignment, and complications were evaluated. Ten eyes were examined on day 3 postoperatively, 13 eyes at 1 to 2 weeks, 10 eyes at 1 to 2 months, five eyes at 3 months, and five eyes at 6 months or later. RESULTS: At 3 days after laser in situ keratomileusis, the surface epithelium and basal epithelium appeared normal. Keratocyte activation was strongest at 1 to 2 weeks and 1 to 2 months, and an increased amount of haze was observed correspondingly. Intrastromal epithelial cells forming a plug could occasionally be perceived in the wound gape. Wound constriction was completed in most cases by 3 to 6 months or later. Good alignment was observed in 12 of 43 flaps (27.9%) and moderate and poor alignment in 17 of 43 flaps (39.5%) and 13 of 43 flaps (30.2%), respectively. Poor alignment was not associated with lamellar epithelial ingrowth. Epithelial ingrowth was associated with dense haze at the interface. Diffuse lamellar keratitis was imaged in two corneas after hyperopic laser in situ keratomileusis. CONCLUSIONS: The laser in situ keratomileusis incision wound at the flap margin appears to heal after the sequence observed in incisional wounds in nonhuman primates. Complications, such as lamellar epithelial in growth and diffuse lamellar keratitis, were often observed, particularly after hyperopic laser in situ keratomileusis.

Adult↗
PubMed2001

Axial length and refractive error in X-linked retinoschisis.

PURPOSE: To examine the relationship between axial length and refractive error in patients with X-linked retinoschisis. DESIGN: To determine whether the hypermetropia frequently found in patients with X-linked retinoschisis is axial hypermetropia. METHODS: The axial length and refractive error were measured in 29 right eyes of 29 patients. The patients were divided into two groups: a juvenile group with ages <13 years (12 eyes) and an adult group with ages > or =13 years (17 eyes). The axial length of the right eye of 30 adult men without eye diseases whose refractive error ranged from +/- 1.0 diopter served as controls. RESULTS: In the adult patient group, the refractive error was significantly more hypermetropic and the axial length was significantly shorter than was the normal adult group (P <.001). CONCLUSION: These results strongly suggest that the hypermetropia in patients with X-linked retinoschisis is axial hypermetropia.

Adolescent↗
PubMed2001

Intraocular lens power calculations using corneal topography after photorefractive keratectomy.

PURPOSE: To report two patients (two eyes) with previous photorefractive keratectomy, who subsequently underwent cataract extraction years later. DESIGN: Case reports. METHODS: Corneal topography was used to determine corneal power used in intraocular lens power calculations. RESULTS: In two eyes of two patients, intraocular lens calculations after photorefractive keratectomy were inadequate, which resulted in a hyperopic postoperative refractive error requiring implantation of a piggyback intraocular lens. CONCLUSION: Corneal topography to determine corneal power in patients with previous photorefractive keratectomy may result in unpredictable intraocular lens power calculations. The clinical history method is the standard to determine corneal power and should be considered in intraocular lens calculations before cataract surgery. We recommend supplying refractive patients with preoperative data for use in future formulas for intraocular lens selection.

Cornea↗
PubMed2002

Rotational malposition during laser in situ keratomileusis.

PURPOSE: To investigate the degree of rotational malposition in eyes undergoing laser in situ keratomileusis. DESIGN: Prospective observational study. METHODS: We measured the rotational position of 240 eyes of 169 patients who underwent treatment for myopic or hyperopic astigmatism with the Alcon Summit Autonomous (Orlando, Florida) LADARVision excimer laser. Immediately preoperatively, each eye was marked while the patient was seated upright. Rotational position was measured on the supine patient immediately before beginning the laser exposure. RESULTS: For all 240 eyes, mean +/- standard deviation (SD) torsional misalignment was 4.1 +/- 3.7 degrees (right eye 3.8 +/- 3.7 degrees, left eye 4.2 +/- 3.6 degrees). A total of 20 eyes (8%) had a deviation of greater than 10 degrees. CONCLUSIONS: A 4 degree and 10 degree misalignment would theoretically result in a 14% and 35% undercorrection of astigmatism, respectively. Preoperative marking of the upright patient and subsequent rotational alignment of the supine patient before laser treatment may reduce the error in correction of astigmatism during excimer laser vision correction surgery.

Astigmatism↗
PubMed2002

Against-the-rule (ATR) astigmatism as a predicting factor for the outcome of amblyopia treatment.

PURPOSE: To evaluate whether with-the-rule (WTR) or against-the-rule (ATR) astigmatism influences the treatment outcome of anisometropic amblyopia. DESIGN: A cohort study. METHODS: Retrospective study of patients with unilateral amblyopia due to anisometropia without strabismus. Ninety-eight patients with simple, compound, mixed, oblique myopic, and hyperopic astigmatism were divided into seven groups based on the type of astigmatism. The groups were reviewed as to the amount of anisometropia, duration of occlusion, and best-corrected visual acuity (BCVA) before and after treatment. RESULTS: There was statistically significant longer duration of occlusion and less lines gain of BCVA among patients with hyperopic ATR astigmatism compared with patients with hyperopic WTR astigmatism (P =.0143 and P =.0000, respectively) and myopic ATR patients compared with myopic WTR patients (P =.0392 and P =.0192, respectively). For the same parameters, group differences were also statistically significant when all hyperopic or myopic simple/compound/mixed ATR patients were compared with all hyperopic or myopic simple/compound/mixed WTR patients (P =.0015 and P =.0000, respectively). CONCLUSION: The outcome of amblyopia treatment seems to be less favorable in patients with either hyperopic or myopic ATR astigmatism. Near vision impairment may be more amblyogenic than distance vision impairment during visual development.

Amblyopia↗
PubMed2003

Mathematical model of corneal surface smoothing after laser refractive surgery.

PURPOSE: To construct a quantitative model of corneal surface smoothing after laser ablation for refractive correction. DESIGN: Experimental study, interventional case series, and meta-analysis of literature. METHODS: A theory of epithelial smoothing in response to corneal contour change is derived from differential equations that describe epithelial migration, growth, and loss. Computer simulations calculate the effects on postoperative epithelial thickness, topography, refraction, and spherical aberration. Model parameter is matched with laser in situ keratomileusis (LASIK) outcome in literature and in a retrospective study of primary spherical myopic (77 eyes) and hyperopic (19 eyes) corrections. Surgically induced refractive change was the main outcome measure. RESULTS: Simulated epithelial remodeling after myopic ablation produces central epithelial thickening, reduction in achieved correction, and induction of oblate spherical aberration. Simulation of hyperopic ablation shows peripheral epithelial thickening, a larger reduction in correction, and induction of prolate spherical aberration. Simulation using a minus cylinder laser ablation pattern shows decreased astigmatism correction and increased hyperopic shift. In the LASIK series, linear regression of achieved correction vs ablation setting in hyperopic and minus cylinder corrections shows slopes of 0.97, 0.71, and 0.74, respectively. These clinical results match model predictions when the smoothing constant is set at 0.32, 0.63, and 0.55 mm, respectively. CONCLUSIONS: Epithelial thickness modulations after ablation can be modeled mathematically to explain clinically observed regression and induction of aberration. The cornea appears to smooth over ablated features smaller than approximately 0.5 mm. The model provides an approach for designing ablation patterns that precompensate for the smoothing to improve final outcome.

Astigmatism↗
PubMed2003

Epidemic and sporadic cases of nontuberculous mycobacterial keratitis associated with laser in situ keratomileusis.

PURPOSE: To report national case-finding results for nontuberculous mycobacterial keratitis and describe its association with laser in situ keratomileusis (LASIK). DESIGN: Enhanced passive disease reporting. METHODS: In April 2001, we investigated a California cluster of Mycobacterium chelonae keratitis associated with hyperopic LASIK using a contact lens mask. To identify other possibly related cases, the American Academy of Ophthalmology e-mailed its members asking them to report recent cases of nontuberculous mycobacterial keratitis to the Centers for Disease Control and Prevention. RESULTS: Forty-three additional cases of keratitis were reported (onsets between August 2000 and June 2001). Of these, 31 occurred as part of two unrelated LASIK-associated outbreaks. The 12 other reported cases occurred in sporadic fashion. Of the latter cases, 4 were associated with LASIK surgery. None of the reported cases were related to the M. chelonae cluster in California. CONCLUSIONS: Laser in situ keratomileusis-associated keratitis with nontuberculous mycobacteria may be more common than previously known.

Cornea↗
PubMed2003

Correcting the corneal power measurements for intraocular lens power calculations after myopic laser in situ keratomileusis.

PURPOSE: To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method. DESIGN: Interventional case series. METHODS: Retrospective analysis of consecutive cases from clinical practice. Two hundred randomly selected eyes from 200 patients were evaluated before and after LASIK surgery. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (Kpre) and post-LASIK K readings (Kpost). We then calculated for each case the pre- and post-LASIK refraction at the corneal plane and the amount of correction obtained by the refractive surgery (CRc). The cases were divided into two groups. Group I was used to derive the two formulas. The K values were calculated using the history-derived method (Kc.hd) in which Kc.hd = Kpre - CRc. Kc.hd was compared with Kpost. The average difference was 0.23 diopters for every diopter of myopia corrected. This value was used to calculate the corneal power using the refraction-derived method (Kc.rd) where Kc.rd = Kpost -0.23CRc. A regression equation was used to develop a clinically derived method (Kc.cd) where Kc.cd = 1.14Kpost -6.8. The values obtained with the two methods were compared with the Kc.hd values in group II to validate the results. RESULTS: Both Kc.rd and Kc.cd values correlated highly with Kc.hd when plotted on a scattergram (P <.001), and there was no statistically significant difference between the mean keratometric values (P >.5). CONCLUSIONS: The corneal power measurements for intraocular lens power calculations after LASIK need to be corrected to avoid hypermetropia after cataract surgery by either the history-derived method, the refraction-derived method, or the clinically derived method.

Adult↗
PubMed1993

Depth of anisometropic amblyopia and difference in refraction.

Disagreement exists as to whether the depth of anisometropic amblyopia correlates with the degree of anisometropia. We reviewed the charts of 303 consecutive patients with the diagnosis of amblyopia. Thirty-five patients with untreated anisometropia without strabismus were identified. The best-corrected visual acuities, manifest refractions, and autorefractions were recorded. The differences in spherical equivalent, root mean square, and an index of anisometropia, which we defined, were calculated. The depth of amblyopia was strongly correlated to all three measures of anisometropia for both hyperopic and myopic individuals. Our new index of anisometropia was an excellent predictor of the depth of amblyopia.

Adolescent↗