Experimental globe rupture after excimer laser photorefractive keratectomy.

OBJECTIVE: To assess corneal weakening after photorefractive keratectomy. METHODS: Photorefractive keratectomy was performed in 16 human eye-bank eyes by means of a 193-nm excimer laser (range, 6 to 54 diopters [D]). Porcine eyes underwent either photorefractive keratectomy procedures (range, 30 to 93 D) with a 5-mm beam diameter or deep 5-mm plano disc ablations. Intraocular pressure was increased gradually with the use of nitrogen gas until the globe ruptured. RESULTS: Human eyes with less than 42 D of correction ruptured at the limbus or behind the insertions of the extraocular muscles. Two eyes showed initial leakage at the 42-D ablation site. Ablations greater than 46 D entered the anterior chamber during treatment. One porcine eye ruptured at the ablation site after a 42-D treatment. Other eyes ruptured at the equator with treatments up to 78 D. CONCLUSION: Excimer laser photorefractive keratectomy does not weaken the cornea after degrees of ablation commonly used in the clinical setting.

Topical nonsteroidal agents and corneal wound healing.

The effects on corneal wound healing of two topical nonsteroidal anti-inflammatory agents, flurbiprofen sodium (0.03%) and diclofenac sodium (0.1%), and the topical corticosteroid, prednisolone sodium phosphate (1%), were evaluated in masked, controlled rabbit studies. Healing of epithelial scrape wounds was significantly retarded in all three treatment groups for the first 3 days after wounding. There was no difference in the epithelial healing rate between the two nonsteroidal or corticosteroid treatment groups. Clinical grading of epithelial quality, conjunctival hyperemia, keratitis, stromal edema, and corneal haze were similar in all groups. There was a significant early decrease in the iritis score in the diclofenac treatment group. The strength of 2-mm central penetrating corneal trephination wounds and the collagen content of these wounds were similar in all groups. Both the topical nonsteroidal anti-inflammatory agents and the corticosteroid used in the preparations and dosages investigated in this study decreased early epithelialization of scrape wounds but had no apparent effect on corneal stromal healing. No toxic effects of the various drugs were found.

The National Basketball Association eye injury study.

OBJECTIVE: To investigate the epidemiology of eye injuries sustained by professional basketball players in the National Basketball Association (NBA). METHODS: A prospective study involving all NBA athletes who sustained eye injuries between February 1, 1992, and June 20, 1993, was conducted. Twenty-seven NBA team athletic trainers, physicians, and ophthalmologists were provided data forms to complete for any player examined for an eye injury. Practice and game exposures during the preseason, regular season, playoffs, and championships were included. RESULTS: Of the 1092 injuries sustained by NBA players during the 17-month period, 59 (5.4%) involved the eye and adnexa. Eighteen (30.5%) of the injuries occurred while the player was in the act of rebounding, and 16 (27.1%) while the player was on offense. The most common diagnoses included 30 abrasions or lacerations to the eyelid (50.9%), 17 contusions (edema and/or ecchymosis) to the eyelid or periorbital region (28.8%), and seven corneal abrasions (11.9%). There were three orbital fractures (5.1%). Most injuries were caused by fingers (35.6%) or elbows (28.8%). Nine players (15.3%) missed subsequent games because of their injury. Fifty-seven players (96.6%) were not wearing protective eyewear at the time of injury. CONCLUSIONS: The incidence of eye injuries in NBA players during the 17-month period was 1.44 per 1000 game exposures. Frequent physical contact in professional basketball players leaves them at great risk for sustaining eye injuries. To prevent these injuries, protective eyewear is recommended.

Tractional venous loops in diabetic retinopathy.

A venous loop developed in a patient with proliferative diabetic retinopathy. Fluorescein angiography showed staining of the vessel wall and nonperfusion of the surrounding capillary bed. Light microscopy and scanning and transmission electron microscopy showed the loop to consist of a telangiectatic retinal vein that had passed through a discontinuity in the internal limiting membrane. The thin-walled vessel loop was lined by an attenuated endothelium and occasional pericytes. The vitreous was detached posteriorly except at the venous loop and a few other points at which there was tenting of the internal limiting membrane. These findings suggested that vitreous traction plays a role in the pathogenesis of these venous loops.

Secondary hemorrhage in traumatic hyphema.

We analyzed the records of 132 patients hospitalized between July 1986 and February 1989 for management of traumatic hyphema. The incidence of secondary hemorrhage was compared between patients treated with or without systemic administration of aminocaproic acid in addition to an otherwise identical protocol. Results among patients who were examined within one day of injury disclosed a 4.8% secondary hemorrhage rate in aminocaproic acid-treated patients (three of 63 patients) compared with a 5.4% rate in the patients not treated with aminocaproic acid (three of 56 patients, P = .31). All six patients sustaining secondary hemorrhage recovered visual acuities of 20/40 or better, with five of six patients achieving 20/20 visual acuities. A separate group of 13 patients who were examined more than one day after injury were found to have a secondary hemorrhage rate of 38.5% (five of 13 patients). Macular injury, not secondary hemorrhage, was most often responsible among those patients suffering permanent visual loss. In this study of a predominantly white population, patients had a relatively low incidence of secondary hemorrhage and did not demonstrate detectable benefit from aminocaproic acid administration. Because of the recognized side effects and cost of treatment, further analysis to determine which patients will benefit from treatment with aminocaproic acid is indicated.

Intraocular pressure increase associated with epsilon-aminocaproic acid therapy for traumatic hyphema.

We treated five patients receiving epsilon-aminocaproic acid who demonstrated sudden and accelerated clot dissolution with accompanying increases in intraocular pressure 24 to 96 hours after discontinuing treatment. All of these patients required additional ocular hypotensive medications and one patient required anterior chamber washout for persistently increased intraocular pressure. These findings suggest that certain patients with hyphema may be at risk for significant intraocular pressure increases following cessation of epsilon-aminocaproic acid therapy.

Photorefractive keratectomy for myopia with a 6-mm beam diameter.

BACKGROUND: Earlier studies have reported clinical outcomes for up to 2 years following photorefractive keratectomy (PRK) using a 5.0-mm treatment zone with the Summit excimer laser. We present results of PRK using a 6-mm ablation zone with the same laser. METHODS: Forty-five eyes of 45 patients underwent excimer laser PRK for correction of myopia using a 6-mm excimer laser beam diameter. Attempted corrections ranged from 1.50 diopters (D) to 6.00 D. Data on outcomes of uncorrected visual acuity, spectacle-corrected visual acuity, predictability, corneal haze, subjective glare/halo effects, and patient satisfaction with the procedure were analyzed over a follow-up period of 6 months. RESULTS: All patients obtained a postoperative uncorrected visual acuity of at least 20/40; 28 eyes (62%) achieved at least 20/20. Postoperative spectacle-corrected visual acuity was at least 20/20 in all patients; no patients lost more than one Snellen line of spectacle-corrected visual acuity. Twenty-eight patients (62.2%) achieved within +/-0.50 D of the attempted correction; 40 patients (84.4%) achieved within +/-1.00 D. Mean spherical equivalent refraction was -4.99 D preoperatively and +0.44 D at 1 month, +0.04 D at 3 months, and +0.09 D at 6 months. At 6 months, 40 eyes (88.9%) were graded as clear, 4 eyes (8.9%) as having trace subepithelial haze, and 1 eye (2.2%) as having mild subepithelial haze. The mean glare/halo index for all of the patients was 0.59 on a scale of 0 to 5. Mean subjective patient satisfaction was 4.68 (on the same scale). CONCLUSIONS: Clinical outcomes following excimer laser PRK for myopia using a 6-mm treatment zone are encouraging. Postoperative subjective glare/halo were minimal, suggesting an optical advantage in using the larger ablation zone.

Photorefractive keratectomy following radial keratotomy.

BACKGROUND: Excimer laser photorefractive keratectomy (PRK) has been used to correct residual myopia in eyes that have had refractive keratotomy. METHODS: Nine eyes of eight patients were studied at a mean of 13 months after PRK. Previous procedures included radial keratotomy (9 eyes) and myopic keratomileusis (1 eye). PRK was performed using a Summit Technology excimer laser with a 5.0-mm diameter ablation zone. RESULTS: Uncorrected visual acuity improved in 7 of 9 eyes. The refractive outcome was within 1.00 diopter (D) of attempted correction for 3 of 9 eyes. Spectacle-corrected visual acuity decreased 2 or more Snellen lines in 2 of 9 eyes. Subepithelial corneal stromal haze was seen 1 month postoperatively in 6 of 8 eyes and was present in 4 of 6 eyes at 1 year. Stromal haze was associated with regression of the refractive effect of the PRK. CONCLUSIONS: PRK in eyes with previous radial keratotomy appears to be less predictable and may be associated with greater corneal haze and regression of refractive correction than in previously unoperated eyes. Activation of stromal fibroblasts in the previous corneal incisions may cause these findings.

Early corneal topography patterns after excimer laser photorefractive keratectomy for myopia.

OBJECTIVES: We defined early patterns of corneal topography following excimer laser photorefractive keratectomy (PRK) with a Summit Apex laser without pretreatment software, investigated changes in patterns over time, and identified factors associated with different topography patterns. METHODS: Fifty-eight eyes of 39 myopic patients were studied. EyeSys videokeratography data were analyzed at 1 week and 1, 2, and 3 months after surgery and were classified using a standardized classification system. RESULTS: At 1 week, 4.3% (n = 2) of corneas showed a homogeneous topography, 0.0% showed a toric-with-axis configuration, 2.2% (n = 1) showed a toric-against-axis configuration, 8.7% (n = 4) showed an irregularly irregular topography, 17.4% (n = 8) showed a keyhole pattern, 23.9% (n = 11) showed a semicircular pattern, 41.3% (n = 19) showed a central island pattern, and 2.2% (n = 1) showed focal topographic variants. From 1 week to 1 month, 78.9% of maps changed; from 1 to 2 months, 33.3% of maps changed; and from 2 to 3 months, 40.0% of maps changed, generally to more regular patterns. The central island pattern, which predominated at 1 week, was not seen at 3 months; most had changed to the keyhole or semicircular pattern. An association was found between the central island pattern and irregularity of reflected rings on the video-image of the cornea (P = .05). CONCLUSIONS: The central island pattern is an early and usually transient topography pattern following PRK. Keyhole and semicircular patterns taken together were the most prevalent in the early postoperative period. In some cases, central islands may be a consequence of corneal epithelial irregularity, and the meridional orientation of the keyhole and semicircular patterns suggests an influence of epithelial healing over time.

Management of late corneal haze following photorefractive keratectomy.

Subepithelial corneal haze and myopic regression are potential complications following excimer photorefractive keratectomy (PRK). There are many medical and surgical methods of managing this haze. We present a 37-year-old male myope who underwent PRK and subsequently developed central corneal haze late in the postoperative course. The haze was managed initially with topical medications with limited success. Mechanical superficial keratectomy was done to remove the superficial scar tissue but the haze returned necessitating repeat excimer laser PRK, using a transepithelial technique. The haze did not recur. Both mechanical superficial keratectomy and repeat excimer laser ablation may ameliorate haze. Success of these procedures may depend on the morphology of the haze and the patient's individual wound healing response.

Topography changes associated with sublamellar epithelial ingrowth after laser in situ keratomileusis.

Laser in situ keratomileusis (LASIK) was performed in 1 eye of a patient for correction of myopia. The patient was evaluated postoperatively using both Placido-disk-based videokeratography and rasterstereography. The patient developed an epithelial defect and subsequent sublamellar epithelial ingrowth after LASIK. The Placido-disk system demonstrated an area of flattening over the area of epithelial ingrowth, and rasterstereography more specifically identified the area over the epithelial ingrowth as an area of relative elevation.

Effect of lamellar flap location on corneal topography after laser in situ keratomileusis.

PURPOSE: To investigate the effect of hinge position on corneal topography after laser in situ keratomileusis (LASIK) for myopia. SETTING: Academic center and refractive surgery practice. METHODS: Topography data obtained from 89 eyes of 46 patients after LASIK were analyzed. Using a system of Cartesian coordinates, data along the horizontal and vertical axes were analyzed, measuring sagittal height and power change at 1 mm intervals from the ablation zone center. Data points that were equidistant and on opposite sides of the ablation center were compared to find asymmetry along either axis relative to nasally hinged flaps. RESULTS: Along the horizontal axis, areas of the cornea closer to the hinge had a higher topography than areas farther from the hinge. Specifically, the points nearest and farthest from the hinge were significantly different in sagittal height (P <.034); the areas farthest from the hinge were reduced more after surgery (relatively lower topography). When results were stratified into low- and high-diopter corrections, this difference was significant in only the high-diopter group (P <.0006). Trends in power change were also observed. Areas of the cornea closer to the hinge were relatively flatter than areas farther from the hinge. Statistical significance was detected in only the low-diopter group at data points 2 mm from the ablation zone center in opposite directions (P <.008). No asymmetry was seen along the vertical axis in power change or sagittal height. CONCLUSIONS: The lamellar flap in LASIK may influence postoperative corneal topography. Hypothetically, the corneal flap may retract toward the hinge, producing axial asymmetry in the postoperative topography relative to the hinge. Understanding the influence of corneal flap characteristics on post-LASIK topography may improve optical results and may be particularly important in the development and effectiveness of topography-guided ablation techniques.

Disparity between refractive error and visual acuity after photorefractive keratectomy: multifocal corneal effects.

PURPOSE: To determine the relationship between postoperative refractive error and uncorrected visual acuity (UCVA) after photorefractive keratectomy (PRK) and compare the results to those in unoperated control eyes with different degrees of myopic refractive error. SETTING: Academic cornea and refractive surgery subspecialty practice. METHODS: Uncorrected visual acuity and manifest refraction were recorded for 52 consecutive patients who had PRK for myopia. Eight control eyes that did not have PRK and in which artificial myopia was induced were also studied to ascertain the association of UCVA with myopia in untreated eyes. Uncorrected visual acuity in postoperative eyes was compared with that in control eyes. RESULTS: Of the 46 eyes with a myopic spherical equivalent postoperative refraction, 44 (96%) had better UCVA than control eyes with equivalent myopic refractions. Twelve of 13 (92%) eyes with refractions of -1.00 diopter or more had a UCVA of 20/40 or better. CONCLUSION: After excimer laser PRK, patients achieved better Snellen visual acuity than might be expected from their residual refractive error, perhaps as a result of a multifocal postoperative corneal topography. Nonuniformity of the corneal surface following PRK may create "focal areas of emmetropia" that allow patients to achieve better visual acuity than the refraction may predict.

Surgically induced astigmatism after photorefractive keratectomy and laser in situ keratomileusis. Summit PRK-LASIK Study Group.

PURPOSE: To compare the axis and magnitude of surgically induced astigmatism in photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Multicenter clinical trial. METHODS: In this prospective randomized trial, 220 eyes of 220 patients entered the study cohort: 105 randomized to PRK and 115 to LASIK. All patients received a single-pass, multizone excimer laser ablation as part of a PRK or LASIK procedure. Attempted corrections ranged from -6.00 to -15.00 diopters (D). The LASIK procedures were performed with nasal hinges. Absolute changes in astigmatism and axis and magnitude of surgically induced astigmatism were analyzed. Patients were followed for up to 6 month. RESULTS: In the PRK group, the mean change in absolute astigmatism was +0.14, +0.16 and +0.32 D at 1, 3, and 6 months, respectively; in the LASIK group, the mean change was -0.15, -0.08, and -0.03 D, respectively. At all time points, a greater proportion of PRK than LASIK eyes had an increase in absolute magnitude of astigmatism. In the PRK group, the axis of vectoral-induced astigmatism was significantly different from random at 3 and 6 months (P = .01, P < .001), respectively) with a tendency for induced with-the-rule shifts postoperatively. In the LASIK group, the axis of vectoral-induced astigmatism was significantly different from random at only 1 month (P = .04), and there was no preponderant direction of axis shift. Despite these findings, other analyses showed no statistically significant between-group differences in vectoral axis or magnitude of surgically induced astigmatism. CONCLUSIONS: Induced astigmatism was generally less and more random in axis in LASIK than in PRK; a general trend for induced with-the-rule astigmatism in PRK was not seen in LASIK. Hypothetically, the lamellar corneal flap in LASIK may counteract the tendency toward steepening at 90 degrees seen in PRK by retracting toward the hinge, by masking underlying induced astigmatism in the ablation zone, or by its mitigating influence on postoperative corneal healing.

Endocapsular hyphema.

A 67-year-old female developed an endocapsular hyphema after uncomplicated extracapsular cataract surgery. With a neodymium:YAG laser capsulotomy, we drained the blood into the vitreous and restored excellent visual acuity. We hypothesize that endocapsular hyphemas may fail to resorb because of sequestration of the clot from the fibrinolytic system of the anterior chamber.

Delayed keratitis after laser in situ keratomileusis.

We report 2 cases of delayed keratitis that occurred after uneventful laser in situ keratomileusis (LASIK). The first patient presented with a peripheral corneal infiltrate 3 months after a LASIK enhancement procedure. The infiltrate progressed despite treatment with topical combination tobramycin-dexamethasone. The flap was then lifted and the interface was irrigated with fortified antibiotics. The keratitis promptly resolved, and the patient recovered a best corrected visual acuity (BCVA) of 20/20. The second patient presented with decreased vision, inflammation, and a sublamellar infiltrate 1 month after primary LASIK. The flap was promptly lifted and irrigated with antibiotics. Cultures were positive for Staphylococcus epidermidis. One week later, the infiltrate had resolved and BCVA had returned to 20/20. Delayed bacterial keratitis has been described as a rare occurrence after incisional refractive surgery. To the best of our knowledge, it has not yet been reported after LASIK. It is important to consider infectious keratitis in the differential diagnosis of a patient who presents with corneal inflammation, even months after having LASIK.

Corneal optical irregularity after excimer laser photorefractive keratectomy. The Summit Photorefractive Keratectomy Topography Study Group.

PURPOSE: To assess the influence of corneal surface microirregularities on objective and subjective visual performance after photorefractive keratectomy (PRK). SETTING: Multicenter clinical trial. METHODS: The alpha version of the Potential Corneal Acuity (PCA) computer program, currently under development, was used to qualitatively and quantitatively analyze the corneal surface of 176 eyes of 176 patients 1 year after PRK. Color maps of corneal surface irregularities were reviewed and quantitative values (PCA) predicting best spectacle-corrected visual acuity (BSCVA) as limited by the cornea were evaluated for associations with qualitative topography patterns, optical zone decentration, and clinical outcomes of BSCVA, uncorrected visual acuity (UCVA), subjective patient satisfaction, and a subjective glare/halo index. RESULTS: Qualitatively, corneas after PRK were generally characterized by a ring of optical irregularity at the juncture of the ablation zone and untreated cornea. Standard corneal topography maps graded as irregular after PRK had a significantly higher PCA value than those graded as regular. There was a trend toward higher PCA values with greater optical zone decentration that was not statistically significant. Actual BSCVA was identical to that which the PCA value predicted in 32% of patients and was within one Snellen line in 71%, within two lines in 89%, and within three lines in 94%. The correlation between the PCA and the glare/halo index and with subjective patient satisfaction was statistically significant. The relationship between PCA and UCVA was not significant. CONCLUSIONS: A ring of optical microirregularity of the corneal surface can appear at the juncture of the treated and untreated cornea after PRK, indicating that the optical zone edge might affect objective and subjective postoperative visual outcomes. Further understanding of corneal surface topography and refinement of the PCA program should help explain visual outcome after PRK.

Photorefractive keratectomy for myopia with a 15 Hz repetition rate.

PURPOSE: To evaluate excimer laser photorefractive keratectomy (PRK) for myopia using a repetition rate of 15 Hz instead of 10 Hz. SETTING: The Cornea and Laser Eye Institute, Teaneck, and Department of Ophthalmology, UMDNJ-New Jersey Medical School, Newark, New Jersey, USA. METHODS: Photorefractive keratectomy using a 15 Hz repetition rate was performed in 23 eyes of 14 patients by a single surgeon at 1 center. The attempted corrections ranged from -2.8 diopters (D) to -5.5 D. Preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), predictability, corneal haze, and subjective glare/halo were evaluated over 6 months. RESULTS: At 6 months, UCVA was 20/32 or better in all eyes and at least 20/20 in 14 eyes (73.7%). Two eyes (10.5%) lost 2 or more Snellen lines of BSCVA; postoperative BSCVA was at least 20/25 in 100% of eyes and 20/20 or better in 95.0%. Fifteen eyes (78.9%) were within +/-0.5 D of attempted correction, and 19 (100%) were within +/-1.0 D. Mean spherical equivalent refraction was -4.62 D preoperatively, +0.15 D at 1 month, -0.09 D at 3 months, and -0.37 D at 6 months. At 6 months, 4 eyes (21.0%) had no corneal haze and 14 (73.7%) had trace subepithelial haze. Fifteen eyes (78.9%) had no glare/halo effect at 6 months, and 4 (21.0%) had minimal glare/halo effect. CONCLUSIONS: Clinical outcomes after excimer laser PRK for myopia using an increased repetition rate of 15 Hz were good and similar to those in studies conducted with a 10 Hz repetition rate.

Penetrating keratoplasty for severe complications of radial keratotomy.

Severe sight-threatening complications were seen in five eyes of three patients following improperly performed radial keratotomy. All patients exhibited neovascularization of the incision sites, severe stromal scarring or ulceration involving the visual axis, loss of the anterior chamber, and iridocorneal adhesions. These complications necessitated multiple and complex surgical interventions, including penetrating keratoplasty and anterior segment reconstruction. Final visual acuity was decreased to light perception in four eyes while one eye achieved 6/60 vision following repeated penetrating keratoplasty. The success and safety of radial keratotomy rely on careful case selection, appropriate instrumentation, specialized training, and the ability to perform complex secondary procedures to correct surgical complications.

Spherical and aspherical photorefractive keratectomy and laser in-situ keratomileusis for moderate to high myopia: two prospective, randomized clinical trials. Summit technology PRK-LASIK study group.

OBJECTIVE: Determine the outcomes of single-zone photorefractive keratectomy (SZPRK), aspherical photorefractive keratectomy (ASPRK), and laser in-situ keratomileusis (LASIK) for the correction of myopia between -6 and -12 diopters. DESIGN: Two simultaneous prospective, randomized, multi-center clinical trials. PARTICIPANTS: 286 first-treated eyes of 286 patients enrolled in one of two studies. In Study I, 134 eyes were randomized to SZPRK (58 eyes) or ASPRK (76 eyes). In Study II, 152 eyes were randomized to ASPRK (76 eyes) or to LASIK (76 eyes). INTERVENTION: All eyes received spherical one-pass excimer laser ablation as part of PRK or LASIK performed with the Summit Technologies Apex laser under an investigational device exemption, with attempted corrections between -6 and -12 diopters. MAIN OUTCOME MEASURES: Data on uncorrected and best spectacle-corrected visual acuity, predictability and stability of refraction, and complications were analyzed. Follow-up was 12 months. RESULTS: At 1 month postoperatively, more eyes in the LASIK group achieved 20/20 and 20/25 or better uncorrected visual acuity than PRK-treated eyes; at the 20/25 or better level, the difference was significant for LASIK (29/76 eyes, 38%) over SZPRK (10/58 eyes, 17%) (P = .0064). At all subsequent postoperative intervals, no difference was seen between treatment groups. Similarly, best corrected visual acuities were better for LASIK than all PRK eyes at 1 month postoperatively, and LASIK was better than SZPRK at 3 months follow-up (e.g., for 20/20 or better at 1 month, LASIK 50/76 eyes (66%) versus SZPRK 24/57 eyes (42%), P = .0066). PRK eyes had a mean loss of BCVA through 6 months, while LASIK eyes had a slight gain of mean BCVA through month 6; at 12 months, both ASPRK groups but not SZPRK continued to have a small mean loss of BCVA (e.g., compared to preoperative, mean BCVA at 12 months for SZPRK was + 0.3, LASIK was +.21, ASPRK I was -0.11, and ASPRK II -0.31 (SZPRK versus ASPRK II, P = .0116). Predictability was better for PRK than LASIK at all follow-up intervals (e.g., for manifest refraction spherical equivalent +/- 1.0 diopters at 6 months, ASPRK I 42/62 eyes (68%) versus LASIK 29/72 eyes (40%), P = .0014%). Stability was slightly but insignificantly less in the LASIK eyes compared to PRK eyes. All visual outcome measures were better for eyes with preoperative myopia between -6 and -8.9 D compared with eyes with myopia between -9 and -12 D. No consistent differences in refractive outcomes or postoperative corneal haze were seen between aspherical and single-zone ablations; haze diminished over 12 months and was judged to be vision-impairing in only one ASPRK eye. Microkeratome and flap complications occurred in 4 eyes, resulting in delay of completion of the procedure in 3 eyes but not causing long-term impairment. CONCLUSIONS: Improvement in uncorrected visual acuity and return of best corrected visual acuity was more rapid for LASIK than PRK, but efficacy outcomes in the longer term through 12 months were similar for all treatment groups. LASIK eyes tended toward undercorrection with the nomogram employed in this study compared to PRK, but the scatter was similar, suggesting little difference between these procedures for most patients by 6 months and thereafter. No consistent advantage was demonstrated between aspherical and single-zone ablation patterns. Predictability was much better for all procedures for corrections of -6 to -8.9 D compared with -9 to -12 D. Sporadic loss of best corrected vision in the PRK eyes not found in the LASIK eyes and other measures of visual function require further study.