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Music is an ever present phenomenon in the lives of adolescents. Although music may be a generic term for expressive sounds ranging from the chants of Tibetian Monks to grandiose performances of Wagnerian opera, for most adolescents the term has a much narrower meaning. This chapter focuses on the involvement of adolescents with popular music that is accessed through public media such as radio and television and the personal media of records, tapes, and compact discs. The existing research validates the assumption that adolescents have a high degree of music media involvement. Unfortunately most of these studies have been based on the assumptions that “adolescents” represent a homogenous population and that “popular music” is a singular genre. Parents, teachers, social workers, and others, who have assumed responsibility for assisting adolescents through their stage of development, look on music as both a problem and a cure.

Music listening is defined as a multifaceted process through which individuals become actively involved in making sense of the sounds, feelings, and associations that are part of the listening experience. This sense-making involves complex mental processes resulting in unique musical experiences created by individual listeners. Listening is a way of doing music. While each listening encounter is highly personalized and covert, various components can be shared through verbal, visual, gestural transductions and these provide a basis for assessing music listening. It is suggested that the emphasis in assessment of music listening be on the degree to which the listener successfully engages in the process of sense-making, rather than being limited to the sounds the listener hears. Examples of assessment strategies are provided.

A field course attended by science teachers in California’s Owens Valley incorporated geospatial technology to reinforce the relationship between elevation, aspect, or the direction a mountain slope faces, and vegetation. Teachers were provided GPS units to record locations and plant communities throughout the 9-day field course. At the end of the field course, they completed an exercise utilizing ArcGIS and/or Google Earth. A similar essay question about vegetation and elevation was answered at the beginning of the course and after the GIS/Google Earth exercise. Scores on this pre- and postactivity question as well as responses to a survey questionnaire indicate that GIS and Google Earth both helped the teachers understand how elevation influences vegetation. The role of aspect was not as well demonstrated in the post-test responses as that of elevation. Teachers reported being more likely to use Google Earth in their classrooms than GIS (75% to 58.3%). Combined with GPS, Google Earth provides a free, easy and flexible way to teach a number of earth science concepts and meet several National Geography Standards.

PURPOSE: To report a case of corneal ectasia after laser in situ keratomileusis (LASIK). The patient presented with minimal alterations in manifest refraction but had obvious distortions in the wavefront error of the eye, as demonstrated by InterWave aberrometry. METHODS: Retrospective case report and literature review. RESULTS: Three years following uneventful and initially successful LASIK and two subsequent enhancement procedures, a patient experienced a decrease in uncorrected and best spectacle-corrected visual acuity with only minor changes in manifest refraction and initially subtle changes on corneal topography. InterWave aberrometry showed a wavefront distortion consistent with progressive steepening of the anterior cornea, reflecting possible development of corneal ectasia. CONCLUSIONS: InterWave aberrometry in conjunction with corneal topography was useful for early recognition of the development of corneal ectasia after LASIK. [J Refract Surg 2004;20: 170-175]

Visual aberrations such as glare and halo have been well documented after laser in-situ keratomileusis (LASIK). These are more likely in patients with higher refractive errors and large pupil diameters. We present a patient with good Snellen acuity but functional impairment by visual aberrations after LASIK. These symptoms resolved after an InterWave-guided LASIK multipass, multistage enhancement treatment to correct spherical aberrations.

To review cases of corneal ectasia after laser in situ keratomileusis (LASIK), identify preoperative risk factors, and evaluate methods and success rates of visual rehabilitation for these cases.Retrospective nonrandomized comparative trial.Ten eyes from seven patients identified as developing corneal ectasia after LASIK, 33 previously reported ectasia cases, and two control groups with uneventful LASIK and normal postoperative courses: 100 consecutive cases (first control group), and 100 consecutive cases with high myopia (8 diopters [D]) preoperatively (second control group).Retrospective review of preoperative and postoperative data for each case compared with that of previously reported cases and cases with uneventful postoperative courses.Preoperative refraction, topographic features, residual stromal bed thickness (RSB), time to the development of ectasia, number of enhancements, final best-corrected visual acuity (BCVA), and method of final correction.Length of follow-up averaged 23.4 months (range, 6-48 months) after LASIK. Mean time to the development of ectasia averaged 16.3 months (range, 1-45 months). Preoperative refraction averaged -8.69 D compared with -5.37 D for the first control group (P = 0.005). Preoperatively, 88% of ectasia cases met criteria for forme fruste keratoconus, compared with 2% of the first control group (P0.0000001) and 4% of the second control group (P = 0.0000001). Seven eyes (70%) had RSB250 microm, as did 16% of eyes in the first control group and 46% of the second control group. The mean RSB for ectasia cases (222.8 microm) was significantly less than that for the first control group (293.6 micro m, P = 0.0004) and the second control group (256.5 microm; P = 0.04). Seven eyes (70%) had enhancements. Only 10% of eyes lost more than one line of BCVA, and all patients eventually achieved corrected vision of 20/30 or better. One case required penetrating keratoplasty (10%), while all others required rigid gas-permeable contact lenses for correction.Significant risk factors for the development of ectasia after LASIK include high myopia, forme fruste keratoconus, and low RSB. All patients had at least one risk factor other than high myopia, and significant differences remained even when controlling for myopia. Multiple enhancements were common among affected cases, but their causative role remains unknown. We did not identify any patients who developed ectasia without recognizable preoperative risk factors.

Objective To study the safety and efficacy of simultaneous bilateral laser in situ keratomileusis (LASIK). Design Prospective randomized clinical trial. Participants Fourteen surgeons and 714 consecutive eyes of 357 patients who desired surgical correction of myopia ranging from −2.00 to −22.50 diopters. Intervention Patients were randomized to simultaneous or sequential bilateral LASIK. Main outcome measures Primary outcome measures were safety and efficacy. Procedure safety was assessed, for simultaneous and sequential groups, by comparison of intraoperative and postoperative complication rates and the percentage of eyes losing two or more lines of spectacle-corrected visual acuity. Procedure efficacy was assessed by comparison of the percentage of eyes with uncorrected visual acuity better than or equal to 20/20 and 20/40 and the percentage of eyes within ±0.50 and ±1.00 diopters of intended outcome. Results Three hundred seventy-eight eyes were enrolled in the simultaneous group, and 331 eyes were enrolled in the sequential group. Mean follow-up was 10 months (±4.2 months standard deviation; range, 2 weeks-22 months). There was no significant difference in intraoperative complication rate ( P = 0.55), loss of two or more lines of spectacle-corrected visual acuity ( P = 0.87), or percentage of eyes within ±0.50 diopters of intended correction ( P = 0.17) between simultaneous and sequential groups. Postoperative complications were not significantly different in the two groups except for the unexplained more frequent epithelial ingrowth in the simultaneous group (2.9%) than in the sequential group (0.6%). The adjusted odds ratio for epithelial ingrowth in the simultaneous group was 1.02 (95% confidence interval, 1.01–1.08). There was no increased likelihood of epithelial ingrowth in the second of two simultaneously treated eyes ( P = 0.95). Conclusion The outcomes and complications of performing bilateral simultaneous LASIK were not significantly different from those of sequential treatments, with the unexplained exception of more frequent epithelial ingrowth in the simultaneous group.

Objective To determine the incidence and severity of complications from laser in situ keratomileusis (LASIK) for the correction of myopia by experienced and inexperienced surgeons. Design Prospective, observational clinical study. Participants Fourteen surgeons and 1062 eyes of 574 myopic patients who desired surgical correction of myopia ranging from −2.00 to −22.50 diopters (D; mean, −7.57 D) and astigmatism no greater than 4.00 D participated in this study. Intervention Myopia was corrected with LASIK. Astigmatism was corrected with arcuate keratotomy at the same time as the initial procedure or subsequently. Main outcome measures Primary outcome measures were change in best spectacle-corrected visual acuity (BSCVA) and the incidence of complications. Results Eyes were followed for a mean of 9.5 months after their last surgical procedure (range, 2 weeks–21 months). Three hundred eighty-one eyes (36%) underwent 468 enhancement procedures 3 months or more after the initial treatment. There were 27 (2.1%) intraoperative and 40 (3.1%) postoperative complications. Laser ablation was not performed during the initial treatment of 17 (1.6%) eyes because of intraoperative complications. Seventy-four eyes gained 2 or more lines of BSCVA, while 50 eyes lost 2 or more lines of BSCVA. Only three eyes lost two or more lines of BSCVA to a level worse than 20/40. One eye with a flap buttonhole (BSCVA 20/50) also had an epiretinal membrane. The second eye (BSCVA 20/60) had a flap buttonhole that may have been related to a previous corneal transplant. The third eye (−22.50 D before surgery) had a rhegmatogenous retinal detachment develop, reducing BSCVA from 20/60 to 20/200. The incidence of intraoperative complications decreased from 3.1% during the first 3 months to 0.7% during the last 9 months of the study ( P = 0.02). Conclusions LASIK is acceptably safe for the correction of myopia. Although complications occur in approximately 5% of cases, these rarely lead to visual loss of more than two Snellen lines and postoperative acuity below 20/40. Flap buttonholes were more likely to cause loss of BSCVA than free or incomplete flaps ( P = 0.02); flap buttonholes may be more likely in eyes that have undergone previous surgery. Complication rates can be reduced as the surgical team gains experience.

Objective This study aimed to determine whether there is a true difference in predictability between single-zone and multizone laser in situ keratomileusis (LASIK) for the correction of low myopia or whether any difference in predictability is because of a need for separate clinical nomograms for the two treatments. Design A prospective, randomized, clinical trial. Participants Fourteen surgeons and 190 eyes of 95 patients with myopia who desired surgical correction of myopia ranging from −2.00 to −7.00 diopters (D) participated. Intervention Fellow eyes of patients with myopia undergoing bilateral simultaneous LASIK were randomized to single-zone and multizone ablation. Astigmatism was not corrected at the time of LASIK. Main outcome measures Predictability, postoperative videokeratography, and contrast sensitivity were assessed at 3 months after surgery. Results At 3 months, r 2 values relating laser setting to change in spherical equivalent refraction were 0.78 for single-zone and 0.76 for multizone ablation; mean outcome with respect to intended was −0.84 D (0.65 standard deviation [SD]) for single-zone and −0.62 D (0.78 SD) for multizone eyes ( P = 0.035). There was no relationship between single-zone and multizone ablation and the likelihood of asymmetric postoperative videokeratography ( P = 0.83). The only difference in contrast sensitivity was a significantly greater decrease in log contrast for multizone eyes at 12 cyc/deg under undilated conditions. Conclusions There is no true difference in predictability between single-zone and multizone LASIK for the correction of low myopia. Separate clinical nomograms for single-zone and multizone LASIK should eliminate the difference in predictability that was observed in this clinical trial.

Objective: The purpose of the study is to determine safety and efficacy outcomes of excimer laser photorefractive keratectomy (PRK) for the treatment of mild-to-moderate myopia. Design: A prospective, multicenter, phase III clinical trial. Participants: A total of 701 eyes of 701 patients were entered in the study; 612 eyes were examined at 2 years after surgery. Intervention: Intervention was photorefractive keratectomy using the Summit ExciMed UV200LA excimer laser (Summit Technology, Inc., Waltham, MA). The treatment zone diameter used was 4.5 mm in 251 eyes (35.8%) and 5 mm in 450 eyes (64.2%). Attempted corrections ranged from 1.50 to 6.00 diopters (D). Main Outcome Measures: Predictability and stability of refraction, uncorrected and spectacle-corrected visual acuity, refractive and keratometric astigmatism, corneal haze, contrast sensitivity, subjective reported problems of glare and halo, and patient satisfaction were the parameters measured. Results: At 2 years, 407 (66.5%) eyes achieved 20/20 or better uncorrected visual acuity and 564 (92.5%) eyes achieved 20/40 or better visual acuity. Three hundred thirty-six (54.9%) eyes were within 0.5 D and 476 (77.8%) eyes were within 1.0 D of attempted correction. Stability of refraction improved with time; 86.8% of eyes were stable within 1.0 D from 6 to 12 months, 94% were stable from 12 to 18 months, and 96.3% were stable from 18 to 24 months. There was no evidence of progressive or late myopic or hyperopic refractive shifts. One hundred fourteen (18.6%) eyes gained 2 or more lines of spectacle-corrected visual acuity, whereas 42 (6.9%) eyes lost 2 or more lines; however, of the latter, 32 (76.2%) had spectacle-corrected visual acuity of 20/25 or better and 39 (92.9%) eyes had 20/40 or better. Four hundred forty-two (72.2%) corneas were clear, 138 (22.5%) showed trace haze, 20 (3.3%) mild haze, 9 (1.5%) moderate haze, and 3 (0.5%) marked haze. On patient questionnaires, 87 (29.7%) patients reported worsening of glare from preoperative baseline; 133 (50.1 %) reported worsening of halo symptoms from baseline. Conclusions: Photorefractive keratectomy appears effective for myopic corrections of −1.50 to −6.00 D. Uncorrected visual acuity is maximized in most eyes by 3 months, although some patients require between 6 months and 1 year to attain their best postoperative uncorrected visual acuity and some may require from 1 to 2 years for stabilization of refraction. Refraction stabilizes progressively without evidence of late myopic or hyperopic refractive shifts. Optical sequelae of glare and halo occur in some patients treated with a 4.5- or 5-mm treatment zone.

Purpose: To identify preoperative and intraoperative characteristics associated with outcomes of photorefractive keratectomy (PRK). Methods: In the phase III multicenter clinical trials of the Summit Technology excimer laser for corrections of 1.5 to 6.0 diopters (D) of myopia, three principal outcomes of PRK on 612 patients were examined: (1) uncorrected visual acuity of 20/40 or better, (2) predictability of refractive outcome within 1.0 D of attempted correction, and (3) stability of refractive result between 12 and 24 months. Multiple logistic regression was used to test for independent associations of multiple preoperative and intraoperative characteristics with each of these outcomes. Results: Older age was independently associated with lesser likelihood of achieving 20/40 or better uncorrected visual acuity (odds ratio=1.08 per incremental year of age, 95% confidence interval [Cl] = 1.04–1.12) and with decreased predictability, specifically with overcorrection (odds ratio=1.09, 95% Cl=1.06–1.12), but age was not associated with stability of refraction. Greater attempted correction was associated independently with a decreased likelihood of 20/40 or better uncorrected visual acuity (odds ratio=2.78 for corrections of 3.5–5.5 D, 95% Cl=1.18–6.75; odds ratio=4.19 for corrections of ≥5.5 D, 95% Cl=1.66–10.58), with decreased predictability (odds ratio=1.72 for corrections of 3.5–5.5 D, 95% Cl=1.05–2.85; odds ratio=2.95 for corrections of ≥5.5 D, 95% Cl=1.65–5.26), and with a reduced likelihood of stability of refraction (odds ratio=3.46 for corrections of ≥5.0 D, 95% Cl=1.32–9.11). No intraoperative characteristics were associated with any of the outcomes assessed. Conclusions: Using this specific excimer laser system with an optical zone of 4.5 or 5.0 mm, patient age and attempted correction are important preoperative characteristics associated with postoperative uncorrected visual acuity and predictability of PRK. Stability of refraction is strongly associated with attempted correction. Such information may help guide patient selection, determine timing of fellow eye treatment, and suggest changes in the laser treatment algorithm for individual patients. Although these findings may be representative of PRK in general, similar analyses should be performed before modifying patient treatments using either a 6.0-mm treatment zone or other laser systems.

• Purpose: We studied the occurrence of late scarring after photorefractive keratectomy and its response to topical corticosteroids and debridement during the course of follow-up of 950 eyes that had photorefractive keratectomy with excimer laser. • Methods: Five eyes of four patients developed localized corneal scars, decreased visual acuity, and increased myopia after five to 33 months of good visual acuity, with trace haze. In two eyes, scars were removed by debridement alone. In these two eyes, recurrent scars were treated by debridement, followed by aggressive treatment with topical corticosteroids. Two other eyes were treated with topical corticosteroids alone. The fifth eye, which developed a scar after debridement to correct a subjective visual distortion after photorefractive keratectomy, was treated with debridement followed by aggressive topical corticosteroids. • Results: Treatment with topical corticosteroids alone in two eyes improved uncorrected visual acuity slightly and decreased myopia, although the scars remained unchanged. Debridement without aggressive topical corticosteroid use resulted in rapid return of the scars and a decrease in visual acuity. Subsequent debridement after aggressive topical corticosteroid treatment resulted in resolution of scars and no recurrence after discontinuation of corticosteroids in one case. In another case, the scar recurred eight months after discontinuation of topical corticosteroids. In Case 4, the scar has not recurred as the topical corticosteroid dosage has been reduced. • Conclusions: Patients who undergo photorefractive keratectomy should be counseled concerning the risk of late scarring, reexamined frequently after photorefractive keratectomy, and treated with topical corticosteroids after corneal trauma. Long-term treatment with topical corticosteroids may be required to prevent the recurrence of scars after debridement.

Many of the deficiencies with human tissue epikeratoplasty might be improved by the use of a suitable synthetic lenticule. Potential biomaterials for epikeratoplasty include collagen (types I1 III, or IV), collagen-hydrogel copolymers, bioactive synthetics, and coated hydrogels. The biomaterial must be engineered to achieve strict specifications of optical clarity, support of epithelial migration and adhesion, permeability to solutes, and stability to corneal proteases. Attaching synthetic lenticules to the cornea without cutting Bowman's layer by adhesives, laser welding, or direct adhesion may also improve the efficacy of synthetic epikeratoplasty. Refract Corneal Surg 1991;7:240-248.)

We used a milliwatt continuous wave CO2 laser mounted on an operating microscope to study the feasibility of welding synthetic collagen epikeratoplasty lenticules to the cornea. In vitro studies and experimentation in rabbits and monkeys showed no welding effects using direct laser radiation with powers ranging from 17 mW to 1 W. Only tissue shrinkage was observed. Experiments using various adjunctive solders produced a temporary welding effect using 30% bovine serum albumin welded with a power of 35-45 mW, 325 urn spot size, moving the beam 5 mm/sec. The lenticules remained in place until the 4th postoperative day when epithelium grew underneath the lenticule, dislodging it. Histopathologic examination demonstrated epithelial migration over the solder displacing the epikeratoplasty lenticule and anterior stromal denaturization and disruption. [Refract /ve and Cornea/ Surgery 1990;6:430-436.]

Excimer laser keratomileusis (photorefractive keratectomy, direct corneal ablation) for myopic corrections of 2.00 diopters (n = 1), 4.00 D (n = 4), and 8.00 D (n = 3) was performed on eight corneas of four Rhesus monkeys. All animals were followed for 18 months. The ablations healed normally and no epithelial erosions occurred. Serial slit-lamp microscope examinations revealed that a variable amount of corneal haze developed in all animals; this haze progressively faded during the follow-up period. Histopathology revealed an epithelium of normal thickness, basement membrane abnormalities, increased number and activity of stromal keratocytes, and a variable amount of newly secreted extracellular matrix in the anterior stroma. These findings suggest that excimer laser keratomileusis induces a mild wound healing response in the anterior cornea which displays considerable individual variability and persists up to 18 months. [Refractive and Corneal Surgery 1990;6:340-345.]

The music education profession supports the idea of mainstreaming, but teachers continue the debate over methods for implementing that idea Keith P. Thompson discusses the philosophy and practice of mainstreaming as it affects music education today.

Purpose: To report the incidence and outcomes of diffuse lamellar keratitis (DLK) after LASIK and to analyze potential causative factors. Methods: Retrospective review of 15,119 cases (11,232 primary procedures and 3887 enhancements) from 7168 patients undergoing LASIK from May 1995 through October 2002, comparing preoperative data and postoperative outcomes for each case developing DLK to patients in the study population and a control series of eyes that did not develop DLK. Results: We identified 61 eyes (0.40%) that developed DLK after LASIK. Three study groups were identified based on sterilization protocols used: (1) steam autoclave without reservoir (8348 cases), (2) cassette autoclave with reservoir (6771 cases), (3) steam autoclave without reservoir and new instrument cleaner (1758 cases). Significantly more eyes developed DLK with Protocol 2 (47 cases, 0.94%) than with Protocol 1(11 cases; 0.1%; P < 0.0001) or Protocol 3 (3 cases, 0.2%; P < 0.0005). There was no significant difference in the incidence of DLK in Protocol 1 versus Protocol 3. DLK was significantly more common after primary procedures than with enhancement procedures only under Protocol 2. No individual developed DLK after more than 1 procedure. Treatment protocols included frequent topical steroids only (24 cases, 39.3%), frequent topical steroids and oral steroids (19 cases, 31.2%), or topical and oral steroids combined with lifting and irrigating beneath the flap (18 cases, 29.5%). Final refractions and visual acuities were not significantly different in eyes that developed DLK and those that did not. Conclusions: DLK is a nonspecific inflammatory response to multiple stimuli that cannot be attributed solely to individual variation in the inflammatory response, the microkeratome, or material deposited by the microkeratome. Sterilizers with reservoirs may cause some cases of DLK. With appropriate diagnosis and treatment, DLK should resolve without sequelae, yielding visual outcomes comparable to cases with uneventful postoperative courses.

To compare visual outcomes in eyes undergoing aberrometry-guided (InterWave) LASIK with those in eyes undergoing standard LASIK treatment based upon refractive measures.Single-center, comparative, interventional, consecutive case series.Four hundred two consecutive eyes undergoing LASIK were analyzed retrospectively. One group, 106 eyes undergoing primary LASIK and 224 eyes undergoing LASIK enhancement, was treated with standard LASIK treatment using a 5.5-mm optical zone, 1.5-mm transition zone laser with the settings determined by manifest refraction. The second group, 44 untreated (primary) eyes and 28 previously treated (enhancement) eyes, received a multipass, multistage treatment in which the laser settings for each stage were determined by aberrometry measurements. Eyes with desired monovision (undercorrected) outcome and preoperative hyperopia were excluded from the study.An aberrometry-guided laser treatment (InterWave LASIK) was compared with the standard LASIK treatment based upon the manifest refraction.Uncorrected visual acuity (VA), manifest refraction, best spectacle-corrected VA (BSCVA), severity of halos, and root mean square (RMS) retinal blur area measured at 3 months postoperatively.Three months postoperatively there was no difference in uncorrected VA, BSCVA, refraction, or RMS retinal blur areas for pupil sizes of 3.5 mm between eyes treated by InterWave and those treated by standard LASIK. However, InterWave LASIK reduced the retinal blur area by 48% (P0.0103) and 58% (P0.0004) in primary cases and 43% (P0.0430) and 74% (P0.0271) in enhancement cases, respectively, for pupil sizes of 4.5 and 6.5 mm relative to standard LASIK treatments. Patients undergoing InterWave-guided treatment reported less severity of halo (0.37 vs. 0.98 [P0.016] for primary cases and 0.35 vs. 0.73 [P0.04] for enhancement cases).InterWave LASIK achieved acuity and refractive results equivalent to those of standard LASIK treatment based upon refraction, but resulted in superior quality mesopic vision.

Objective The purpose of this study was to define qualitative patterns of videokeratography after excimer laser in situ keratomileusis (LASIK) for myopia and to identify associations of videokeratography patterns with clinical variables. Design Single-center, retrospective, cohort study. Participants One hundred twenty-six eyes of 68 patients with myopia who desired surgical correction of myopia ranging from −1.50 to −8.80 diopters. Intervention Myopia was corrected with LASIK using a Summit OmniMed/Apex excimer laser. Computer-assisted videokeratography data were acquired at 3 months after primary LASIK, and associations of videokeratography pattern with clinical variable were assessed. Main outcome measures Seven subgroup ablation zone patterns were characterized using tangential curvature maps; these subgroups were combined into pooled symmetric and asymmetric groups. Associations with age, attempted correction, single-zone or multizone ablation, postoperative uncorrected and spectacle-corrected visual acuity, predictability, astigmatism, corneal uniformity, glare disability, and contrast sensitivity were analyzed. Results Thirty-two eyes (25.4%) showed a uniform pattern, 14 eyes (11.1%) showed a bow-tie pattern, 22 eyes (17.5%) showed a peninsula pattern, 22 eyes (17.5%) showed a semicircular pattern, 22 eyes (17.5%) showed an off-center blue spot pattern, 10 eyes (7.9%) showed an irregular pattern, and 4 eyes (3.2%) showed a central island pattern. Spectacle-corrected visual acuity, astigmatism, corneal uniformity, glare disability, and contrast sensitivity were significantly related to videokeratography pattern, although the difference among videokeratography groups was clinically small. Age, attempted correction, single- or multizone ablation, and postoperative uncorrected visual acuity and predictability were not predictive of videokeratography pattern. Conclusions Most eyes in this study had an asymmetric videokeratography pattern 3 months after LASIK. Small but statistically significant differences were identified among the videokeratography patterns that potentially may affect postoperative quality of vision.

Purpose To assess the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium. Methods In a prospective study, the corneal endothelium of 98 eyes of 65 consecutive patients (mean age, 41 years; range, 22 to 66 years) was photographed before, 2 weeks after, and 12 weeks after LASIK for the correction of 2.75 to 14.5 diopters of myopia. Theoretical ablation depths were 200 to 330 μm below the corneal surface. Cell density, coefficient of variation, and percent of hexagonal cells were determined using 150 to 200 cells from each image. Eighty-eight eyes (91%) of 59 patients had a history of contact lens wear. Results The mean ± SD preoperative endothelial cell density was 2,549 ± 365 cells per mm 2 , and the mean coefficient of variation was 0.35 ± 0.06. There was no statistically significant change in the mean endothelial cell density or mean coefficient of variation of cell size at the 2-week (2,561 ± 360 cells per mm 2 and 0.35 ± 0.06) or 12-week (2,541 ± 364 cells per mm 2 and 0.35 ± 0.05) postoperative examinations. The percent of hexagonal cells was not significantly changed 2 weeks postoperatively; however, 12 weeks postoperatively ( P =.0413, two-tailed t test), the percent of hexagonal cells was decreased by 1%. Conclusions Corneal endothelial cell density and morphology were unchanged 2 and 12 weeks after LASIK for the correction of up to 14.5 diopters of myopia. In this LASIK study, the correction of up to 14.5 diopters of myopia appears to cause no clinically significant effect on corneal endothelial cell density or morphology.

Purpose: ^The authors prospectively investigated the effect of excimer laser photorefractive keratectomy (PRK) for myopia on the corneal endothelium. Methods: Quantitative computer-assisted morphometric analysis of central and peripheral corneal endothelial cells was performed on 142 myopic eyes before and at 3 months, 1 year, and 2 years after PRK. The mean age of the subjects was 37 years (range, 21-66 years). Ninety-one (64%) of them had a history of contact lens wear. Mean attempted correction was -3.9 diopters (range, -1.6 to -6.0 diopters). Results: The mean preoperative endothelial cell density was 2660 cells/mm2 centrally and 2776 cells/mm2 peripherally. There was no change in central endothelial cell density at any of the postoperative examinations. The peripheral cell density decreased 4.1 % ( P = 0.003) at 3 months and 6.2% ( P = 0.0001) at 1 year. However, the peripheral cell density was not significantly different from the preoperative value at 2 years. The peripheral coefficient of variation of cell size was 7.8% lower 2 years postoperatively than it was preoperatively, and this improvement was attributable to cessation of contact lens wear after PRK. The decrease in peripheral endothelial cell density at 1 year correlated with the amount of attempted correction, but there was no correlation between attempted correction and the change in central or peripheral endothelial cell density 2 years postoperatively. Conclusion: For the correction of up to 6.0 D of myopia, PRK causes no detectable changes in central corneal endothelial cell density, but it does cause a transient, modest loss of peripheral corneal endothelial cells at 1 year. Variations in endothelial cell shape caused by contact lens wear resolve after PRK.