Long-term results of thin corneas after refractive laser surgery

PURPOSE: To report the long-term refractive results of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in patients with thin corneas. DESIGN: A long-term, retrospective, non-randomized follow-up study. METHODS: Sixty-three patients (124 eyes) (28 males and 35 females), who had a preoperative central corneal thickness (CCT) of less than 500 microns and completed at least one year of follow-up examinations after surgery. Thirty-five patients (68 eyes) underwent PRK and 28 patients (56 eyes) underwent LASIK. RESULTS: Mean preoperative corneal pachymetry was 484.95 +/- 6.65 microm (range, 470 to 498 microm) and 482.38 +/- 10.73 microm (range, 453 to 499 microm) for LASIK and PRK, respectively. No intraoperative complications were found in both groups. None of the included eyes developed postrefractive corneal ectasia. The mean predictability for the PRK group was 0.08 diopters (D) with a standard deviation of 0.40 D (range, -1.38 to 1.00 D), and the mean predictability for the LASIK group was 0.14 D with a standard deviation of 0.55 D (range, -1.25 to 1.33 D). CONCLUSIONS: Refractive laser surgery with LASIK or PRK in patients with thin corneas (less than 500 microm) seems to be a safe and predictable technique for myopic refractive corrections.     

Changes in the posterior cornea after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To study the changes in posterior corneal elevation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using Scheimpflug topography with the Pentacam anterior segment imaging system (Oculus, Inc.). SETTING: Department of Ophthalmology, Albany Medical Center, and a private clinical practice, Albany, New York, USA. METHODS: In this prospective study, 121 consecutive myopic eyes (103 LASIK and 18 PRK) were evaluated preoperatively and postoperatively with the Pentacam to determine elevation changes in the posterior corneal surface. Changes in posterior elevation were calculated by comparing the best-fit sphere preoperatively and postoperatively to a fixed reference sphere using the central 9.0 mm preoperative cornea. Statistical and graphic analyses were performed. RESULTS: The 103 LASIK eyes had a mean correction of -3.76 diopters (D) and a mean ablation depth of 62.1 microm. The mean estimated residual bed thickness (RBT) (329 microm) demonstrated a mean posterior displacement of 2.64 +/- 4.95 microm. The 18 PRK eyes had a mean correction of -2.69 D and a mean ablation depth of 53.2 microm. The mean estimated RBT (464 microm) had a mean posterior displacement of -0.88 +/- 4.64 microm. The difference in the mean posterior corneal displacement between the LASIK and the PRK eyes was not statistically significant (P>.05, Student t test). CONCLUSIONS: There was no statistically significant difference in posterior corneal displacement between the LASIK and PRK patients. The changes in PRK and LASIK eyes appeared to be within acceptable measurement variation. Contrary to previous reports, ectatic changes to the posterior corneal surface did not routinely occur after LASIK surgery.     

Role of the corneal epithelium in refractive changes following laser in situ keratomileusis for high myopia

PURPOSE: Epithelial hyperplasia is one of the factors that plays a role in myopic regression after photorefractive keratectomy (PRK). We evaluated the role of the epithelium following excimer laser in situ keratomileusis (LASIK) performed on highly myopic eyes. METHODS: Fifty eyes of 32 patients (18 females and 14 males; mean age, 31.7+/-6.5 years) were treated with LASIK for myopia with an attempted correction ranging between -8.50 and -12.25 D (mean, -10.48+/-1.43 D). No sutures were placed. The thickness of the central epithelium was evaluated either with a 50-MHz ultrasonic pachymeter or an ultrasound biomicroscope. Postoperatively, topical corticosteroid drops were administered for at least 1 month. RESULTS: Follow-up was at least 12 months. Epithelium measurements were thicker compared to preoperative measurements from the first week postoperatively (mean, +1.9 microm, +2.77%; P<.05). Epithelial thickness peaked at the third month after LASIK (mean, +6.5 microm, +9.5%; P<.05) and remained stable through 12 months. A negative correlation between epithelium thickness and manifest refraction from the first month postoperatively to the end of follow-up was present. CONCLUSION: The epithelium seemed to have a role in the regression of refractive effect after LASIK to correct high myopia.     

Laser in situ keratomileusis and photorefractive keratectomy for residual refractive error after phakic intraocular lens implantation

PURPOSE: To determine the visual and refractive outcome of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in eyes with prior posterior chamber phakic intraocular lens implantation for high myopia. METHODS: We studied a series of 37 consecutive eyes of 31 patients who underwent LASIK or PRK for residual refractive error following collamer posterior chamber intraocular lens (IOL) (Staar Surgical Implantable Contact Lens) implantation into a phakic eye. Twenty-eight eyes had LASIK and nine eyes had PRK. Mean follow-up was 8.1 +/- 4.7 months after laser ablation (range, 3 to 18 mo). RESULTS: The preoperative mean spherical equivalent refraction prior to phakic posterior chamber IOL implantation was -17.74 +/- 4.89 D (range, -9.75 to -28.00 D). Following phakic IOL implantation and prior to LASIK or PRK, mean spherical equivalent refraction was -2.56 +/- 2.34 D (range, -0.25 to -8.75 D). One month following LASIK or PRK, mean spherical equivalent refraction was -0.24 +/- 0.52 D (range, -1.50 to +1.50 D), 3 months following LASIK or PRK, mean spherical equivalent refraction was -0.19 +/- 0.50 D (range, -1.50 to +1.00 D). The refraction was within +/-1.00 D of emmetropia in 36 eyes (97.2%) and within +/-0.50 D in 31 eyes (83.7%). Three eyes developed anterior subcapsular opacities several weeks after laser ablation, one eye developed macular hemorrhage 4 weeks after laser ablation, and one eye had corticosteroid induced ocular hypertension. CONCLUSIONS: LASIK or PRK can be used to treat the residual refractive error following posterior chamber phakic IOL implantation.     

Evaluation of photorefractive keratectomy retreatments after regressed myopic laser in situ keratomileusis

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) enhancements in eyes previously treated by myopic laser in situ keratomileusis (LASIK) showing an undercorrection due to either a refractive regression or a primary undercorrection, when an in-the-bed enhancement was not advisable because of residual stromal thickness limitations. DESIGN: Noncomparative, prospective, interventional case series. PARTICIPANTS: Seventeen eyes of 17 patients previously treated by LASIK for a spherical equivalent (SE) correction of -8.125 to -12.50 diopters (D; mean, -9.45 +/- 1.01 D), that after a follow-up of 6 to 14 months ended up with a refraction of -1.50 to -3.75 D (SE; mean, -2.48 +/- 0.74 D). Intended flap thickness was 160 microm for all eyes. In all cases, the residual stromal bed under the flap was considered too thin (255-305 microm) to allow an in-the-bed enhancement without exceeding an assumed safety thickness limit (250 microm). INTERVENTION: Eyes were treated by PRK at least 6 months after LASIK. The PRK ablation parameters (diameter, attempted correction) were selected to avoid theoretical flap perforation. The deepest ablation was 60 microm, for a -3.75-D correction. We used a Bausch & Lomb 217 C excimer laser (Bausch & Lomb, Rochester, New York). MAIN OUTCOME MEASURES: Refraction, uncorrected and best-corrected visual acuity (BCVA), slit-lamp evidence of corneal opacity or other visible complications, and corneal topography. RESULTS: Although the initial postoperative period was characterized by very satisfactory refractive results (mean SE error at 1 month, -0.04 +/- 0.37 D; range, +0.75 to -0.625 D), during follow-up, a dense haze (grade 3 and 4) developed in 14 eyes (82.3%) that induced a further myopic regression (SE, -1.725 to -5.50 D; mean, -3.11 D) and BCVA loss (two to six lines). These 14 eyes underwent a further surgical treatment to remove the severe haze at 3 to 10 months after PRK. CONCLUSIONS: Based on these results, we strongly advise against PRK as a possible option to correct eyes previously treated by myopic LASIK that resulted in an undercorrection.     

TOSCA治疗复杂屈光不正的临床疗效观察

目的:评价角膜地形图引导的个体化切削术治疗复杂屈光不正的临床疗效。方法:选择接受TOSCA治疗的复杂屈光不正患者共59例113眼。其中近视度数相对高角膜厚度相对薄67眼,角膜形态不规则8眼,角膜散光大33眼,PRK/LASIK术后偏心切削6眼,PRK/LASIK术后再近视5眼。术前等效球镜为平均-1.25～-13.88(平均-6.87±2.86)D。观察术后裸眼视力(uncorrected visual acuity,UCVA)、最佳矫正视力(best-corrected visual acuity,BCVA)、等效球镜、角膜曲率、角膜厚度、高阶像差及偏中心切削等。结果:UCVA术前为0.13±0.12,术后6mo为0.94±0.22,差异有统计学意义(P<0.05)。术后6mo时的平均等效球镜为(-0.45±0.48)D,在±0.5D以内。角膜曲率术前为(43.01±1.56)D,术后6mo为(37.99±1.69)D,术后与术前比较显著降低,差异有统计学意义(P<0.05)。术中平均切削厚度为(88.30±28.86)μm,比按照其相同屈光度和切削直径的传统LASIK/LASEK手术的切削厚度(117.93±32.72)μm节约了约(27.77±23.24)μm,差异无统计学意义(P>0.05)。术前总高阶像差、水平彗差、垂直彗差及球差值分别为0.50±0.23,0.10±0.08,0.14±0.12,0.12±0.09,术后6mo时分别为0.68±0.25,0.21±0.22,0.32±0.18,0.38±0.14,差异有统计学意义(P<0.05)。术前6例因PRK和LASIK术后造成的偏中心切削,其偏中心切削距离均>1.0(平均1.33±0.45)mm,术后偏中心切削平均为(0.49±0.22)mm,差异有统计学意义(P<0.05)。结论:TOSCA治疗复杂屈光不正术后有较好的安全性、有效性和预测性,且可以在一定程度上节约角膜厚度。     

Comparison of laser in situ keratomileusis and photorefractive keratectomy results: long-term follow-up

PURPOSE: To compare the results of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) over a 4-year follow-up. SETTING: Miyata Eye Hospital, Miyazaki, Japan. METHODS: This comparative retrospective study comprised 22 eyes (22 patients) that had PRK and 18 eyes (18 patients) that had LASIK. To be included, the patient had to have completed a 4-year follow-up. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), percentage of eyes within +/-0.5 diopter (D) of the targeted refraction, central corneal thickness, and the anterior and posterior corneal elevations were compared between the PRK and LASIK groups. RESULTS: The mean UCVA was significantly better in the LASIK group than in the PRK group at 6 months (P = .0043) and 1 year (P = .0044). At 2 years, there was no significant difference in the mean UCVA between the 2 groups. The mean BSCVA was significantly better in the LASIK group than in the PRK group at 6 months (P<.0001), 1 year (P<.0001), and 2 years (P = .0083). At 3 and 4 years, there was no significant difference in the mean BSCVA between the 2 groups. The percentage of eyes within +/-0.5 D of the targeted refraction was not significantly different between groups at any time. CONCLUSIONS: The superiority of LASIK over PRK in short-term efficacy was not retained 4 years after surgery. The main reasons were a myopic shift and a decline in UCVA at the last follow-up in the LASIK group.     

Corneal power, thickness, and stiffness: results of a prospective randomized controlled trial of PRK and LASIK for myopia

PURPOSE: To compare the short-, medium-, and long-term changes in corneal optical power and corneal aberrations, central corneal thickness, and corneal "stiffness" assessed by pneumotonometry readings in patients having laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) for myopia. SETTING: Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. METHODS: One eye of each of 45 patients with myopia ranging from -6.00 to -8.00 diopters (D) (spherical equivalent spectacle refraction [SER]) was randomized to LASIK (n=25; mean SER -7.12 D +/- 0.57 [SD]) or PRK (n=20; mean SER -6.91 +/- 0.57 D). Data were collected prospectively before and 1, 3, 6, 12, and 36 months after surgery. Measurements included corneal topography (TMS-1, Tomey), corneal thickness (ultrasound pachymetry), and apparent intraocular pressure (IOP) (pneumotonometry). Retreatments were not performed during the first year, and retreated eyes were excluded from the 3-year follow-up. Changes in corneal power and aberrations, thickness, and apparent IOP were calculated in a pair-wise manner for 3 time periods: short term (preoperative to 1 month after surgery), medium term (1 to 12 months after surgery), and long term (1 to 3 years after surgery). RESULTS: In the short term, corneal power decreased equally in LASIK and PRK eyes. Spherical aberrations and coma-like aberrations increased equally, while corneal thickness decreased significantly less in LASIK eyes than in PRK eyes. The apparent IOP decreased more in LASIK eyes than in PRK eyes. In the medium term, corneal power increased significantly in both groups. Spherical aberrations decreased significantly in PRK eyes but not in LASIK eyes. From 1 to 12 months, corneal thickness increased more in PRK eyes than in LASIK eyes. During this period, the apparent IOP increased significantly in LASIK eyes. In the long term, corneal power and corneal aberrations did not change significantly in either group. Corneal thickness increased slightly but significantly in both groups. The apparent IOP increased significantly more in PRK eyes. CONCLUSIONS: Differences between LASIK and PRK related to time-dependent events affecting corneal shape and structural integrity were present. Peripheral changes in flap hydration in LASIK eyes and epithelial and/or stromal thickening in PRK eyes appeared to be the most important factors in optical power changes in the first year after treatment. The changes in apparent IOP suggest that some interlamellar healing occurred during the first year after LASIK. After LASIK and PRK, corneal bending stiffness seemed permanently decreased, although some restiffening may occur in PRK eyes in the long term.     

Comparison of laser in situ keratomileusis and photorefractive keratectomy for the correction of myopia of -6.00 diopters or less. Melbourne Excimer Laser Group

PURPOSE: To evaluate the safety and efficacy of laser in situ keratomileusis (LASIK) compared to photorefractive keratectomy (PRK) for the correction of low or moderate myopia (-0.50 to -6.00 D) at 6 months after surgery. METHODS: The study population comprised a non-randomized consecutive series of 622 eyes of 392 patients who were treated with the Nidek EC-5000 excimer laser. LASIK was performed using the ACS Chiron microkeratome on 314 eyes and surface PRK on 308 eyes. All patients were treated using a standard protocol, then assessed at 1, 3, and 6 months postoperatively. RESULTS: Forty-four percent of the LASIK group and 67% of the PRK group attended their 6-month examination. Eighty percent of patients (111 eyes) after LASIK and 65% (136 eyes) after PRK had an uncorrected visual acuity of 20/20 or better. Spherical equivalent refraction was within +/-0.50 D of intended refraction in 78% (109 eyes) for LASIK and 82% (170 eyes) for PRK. Loss of two more lines of best spectacle-corrected visual acuity at 6 months occurred in 1.4% (2 eyes) of the LASIK group and 1.0% (2 eyes) of the PRK group. CONCLUSION: At 1 month follow-up, the percentage of eyes that achieved 20/20 uncorrected visual acuity was greater in the LASIK group than in the PRK group. At 6 months, visual and refractive outcomes of LASIK and PRK were similar. Although flap related complications occurred only after LASIK, the overall risk of loss of best spectacle-corrected visual acuity was not significantly greater than for PRK.     

Photorefractive keratectomy with mitomycin C versus LASIK in custom surgeries for myopia: a bilateral prospective randomized clinical trial

PURPOSE: To compare photorefractive keratectomy (PRK) with prophylactic use of mitomycin C (MMC) and LASIK in custom surgeries for myopic astigmatism. METHODS: Eighty-eight eyes of 44 patients with a minimum estimated ablation depth of 50 microm were randomized to receive PRK with MMC 0.002% for 1 minute in one eye and LASIK in the fellow eye. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), cycloplegic refraction, slit-lamp microscopy, contrast sensitivity, specular microscopy, aberrometry, and a subjective questionnaire were evaluated. Forty-two patients completed 6-month follow-up. RESULTS: Mean spherical equivalent refraction error before surgery and mean ablation depth were -3.99+/-1.20 diopters (D) and 73.09+/-14.55 microm in LASIK eyes, and -3.85+/-1.12 D and 70.7+/-14.07 microm in PRK with MMC eyes, respectively. Uncorrected visual acuity was significantly better in PRK with MMC eyes 3 months (P=.04) and 6 months (P=.01) after surgery. Best spectacle-corrected visual acuity and spherical equivalent refraction did not differ significantly in the groups during follow-up (P>.05). Significant haze was not observed in any PRK with MMC eye. Mean higher order aberration was lower in PRK with MMC eyes postoperatively compared with LASIK eyes (P=.01). Better contrast sensitivity was observed in PRK with MMC eyes than LASIK eyes (P<.05). The endothelial cell count did not differ significantly between groups (P=.65). In terms of visual satisfaction, PRK with MMC eyes were better rated. CONCLUSIONS: Photorefractive keratectomy with MMC appears to be more effective than LASIK in custom surgery for moderate myopia. During 6-month follow-up, no toxic effects of MMC were evident. Long-term follow-up is necessary to attest its safety.     

Confocal microscopy changes in epithelial and stromal thickness up to 7 years after LASIK and photorefractive keratectomy for myopia

PURPOSE: To determine the long-term changes in epithelial, stromal, and corneal thickness after LASIK and photorefractive keratectomy (PRK). METHODS: In two prospective observational case series, 11 patients (16 eyes) received LASIK and 12 patients (18 eyes) received PRK to correct myopia or myopic astigmatism. None of the corneas had retreatment procedures. Corneas were examined using confocal microscopy before and at 1 month, and at 1, 2, 3, 5, and 7 years after surgery. Central thicknesses were measured from reflected light intensity profiles recorded by confocal microscopy. Postoperative epithelial thickness was compared to preoperative, and postoperative stromal and corneal thicknesses were compared to thickness at 1 month after surgery. RESULTS: In LASIK, epithelial thickness at 1 month (51 +/- 4 microm, n = 11) was greater than before surgery (41 +/- 4 microm, n = 16; P < .001) and remained thicker through 7 years (52 +/- 6 microm, n = 13; P < .001). Stromal and corneal thickness did not change between 1 month and 7 years after LASIK. After PRK, corneal thickness at 1 year (464 +/- 44 microm, n = 17) was greater than at 1 month (442 +/- 39 microm, n = 15; P = .001) and remained thicker at 7 years after PRK (471 +/- 45 microm, n = 17; P > .001). CONCLUSIONS: The early increase in central epithelial thickness after myopic LASIK persists for at least 7 years and is probably the result of epithelial hyperplasia. Central corneal thickness increases during the first year after PRK and remains stable thereafter up to 7 years.     

Stromal wound healing explains refractive instability and haze development after photorefractive keratectomy: a 1-year confocal microscopic study

PURPOSE: To evaluate the mechanism(s) producing refractive instability and corneal haze development after photorefractive keratectomy (PRK). DESIGN: Prospective, nonrandomized, comparative case series, self-controlled. PARTICIPANTS: Seventeen eyes of 17 patients with low- to moderate-grade myopia (-2.88 to -9.13 diopters [D]) were included. METHODS: Surgical intervention was a standardized, 6-mm diameter PRK procedure using the Meditec MEL 60 excimer laser (Aesculap-Meditec, Heroldsberg, Germany). The photoablation center was evaluated before surgery and at 1, 3, 6, 9, and 12 months after PRK using rapid, continuous z-scans of confocal images, termed confocal microscopy through focusing (CMTF). MAIN OUTCOME MEASURES: Simultaneous epithelial and stromal thickness analysis and objective assessment of corneal light backscattering were obtained from digital image analysis of the CMTF scans. Corneal reinnervation and anterior stromal keratocyte density and wound healing morphologic features were evaluated on high resolution, in vivo confocal images. Manifest refraction was measured and corneal clarity was graded by slit-lamp biomicroscopy. RESULTS: Epithelial thickness averaged 45+/-10 microm at 1 month, 50+/-8 microm at 3 months, and 52+/-6 microm at 12 months after PRK, as compared with 51+/-4 microm before surgery, demonstrating complete restoration of the preoperative thickness without compensatory hyperplasia. Interestingly, epithelial rethickening had no significant correlation with refractive regression. By contrast, stromal regrowth (from 1-12 months) averaged 6+/-12 microm (range, 27 microm thinning-22 microm rethickening) and correlated closely (r = 0.84, P<0.001) with changes in refraction that averaged 0.84+/-1.23 D, ranging from -1.63 D (hyperopic shift) to +3.38 D (myopic regression). Stromal rethickening increased proportionally with the actual photoablation depth (r = 0.63, P<0.01); linear regression analysis suggested an average regrowth rate of 8% per year for the entire study group. Stromal rethickening was not associated with CMTF haze development over time, suggesting that haze and regression were caused by two independent wound healing mechanisms. In agreement with these findings, all "hazy" corneas showed increased numbers of anterior stromal wound healing keratocytes with increased reflectivity of both nuclei and cell bodies, suggesting that cellular-based reflections, as opposed to extracellular matrix deposition, are the major origin of increased corneal light scattering after PRK. CONCLUSIONS: Taken together, these data indicate that keratocyte-mediated regrowth of the photoablated stroma appears to be the main cause of myopic regression in humans treated with a 6-mm diameter PRK, whereas hyperopic shifts appear to be a direct consequence of stromal thinning. By contrast, the corneal epithelium appeared to restore its preoperative thickness without contributing significantly to the refractive changes after PRK. Finally, this study also provides strong evidence that the development of haze after PRK is directly associated with increased cellular reflectivity from high numbers of wound healing keratocytes.     

Absence of keratectasia after LASIK in eyes with preoperative central corneal thickness of 450 to 500 microns

PURPOSE: To determine whether preoperative central corneal thickness less than or equal to 500 microm is an independent risk factor for development of keratectasia following LASIK. METHODS: Chart review was performed for 109 eyes with preoperative central corneal thickness of 452 to 500 microm in 69 patients who underwent LASIK between September 2000 and July 2005 and had no known risk factors for keratectasia. All eyes included in this analysis had postoperative manifest refractions at follow-up at 1-month and 12-months or greater (median: 452 days; range: 365 to 1980 days). RESULTS: Attempted correction (spherical equivalent refraction) ranged from +3.13 to -7.75 diopters. There were no clinical signs of keratectasia at any postoperative visits in the 109 eyes in this study. There was no statistically significant change in mean spherical equivalent or manifest cylinder from the 1-month follow-up examination to the last documented visit (12 months or greater). No correlation was found for preoperative pachymetry and refractive change between postoperative examinations at 1 month and 12 months or greater. Double-angle vector analysis determined the directional shift in postoperative refractive cylinder was not statistically significant from zero (P > .05). CONCLUSIONS: In this group of 109 LASIK-treated eyes with preoperative central corneal thickness less than or equal to 500 microm that were screened for known keratectasia risk factors, there was no evidence of postoperative keratectasia.     

Influence of flap thickness on results of laser in situ keratomileusis for myopia

PURPOSE: To study whether flap thickness influences laser in situ keratomileusis (LASIK) results. METHODS: This comparative, non-randomized, retrospective study comprised 421 LASIK eyes (233 patients) with spherical equivalent refraction between -0.60 and -6.00 diopters (D). Laser in situ keratomileusis was performed with the Moria One manual microkeratome and the Chiron Technolas 217C laser. Depending on the flap thickness, the eyes were divided into three groups (group 1, flap thickness < or =100 microm; group 2, flap thickness > 100 microm and < 130 microm; and group 3, flap thickness > or = 130 pm). For each group uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity, residual spherical equivalent refraction, and keratometric power (D) were measured 1 day, 1 week, 1 month, and 6 months after LASIK. Complications, retreatment, and correlation between flap thickness and preoperative corneal thickness and keratometric power were also analyzed. RESULTS: One month postoperatively, UCVA was > or = 20/20 in 76% (96 eyes), 56% (79 eyes), and 61% (93 eyes) of eyes in the three group, respectively (P = .015). One month postoperatively, UCVA was > or = 20/25 in 88% (111 eyes), 76% (108 eyes), and 76% (116 eyes) of eyes in the three groups, respectively (P = .015). Complication rate and retreatment rate were not statistically different among the groups. At 6-month follow-up, no statistically significant differences were noted in UCVA between the groups. Significant correlations between flap thickness and preoperative corneal thickness (P < .0001) and between flap thickness and preoperative keratometric power (P < .05) were found. CONCLUSION: Patients with flaps < or = 100 pm had better functional results at 1 month than those with thicker flaps. It may be important to perform LASIK with thin flaps to save corneal tissue in the stromal bed.     

Keratectasia after LASIK but not after PRK in one patient

PURPOSE: To report a case of keratectasia in a patient who underwent LASIK in the right eye and photorefractive keratectomy (PRK) in the left eye for correction of compound myopic astigmatism. METHODS: A 30-year-old man underwent LASIK in the right eye and PRK in left eye for refraction of -1.75 -1.50 x 48 degrees and -1.00 -1.75 x 100 degrees, respectively. Preoperative corneal thickness was 447 microm in the right eye and 446 microm in the left eye. RESULTS: Postoperative corneal thickness decreased to 341 microm and 384 microm in the right and left eye, respectively. Uncorrected visual acuity in the left eye was 20/20, but the right eye developed keratectasia, which led to severe visual loss (20/400). CONCLUSIONS: Photorefractive keratectomy may be better than LASIK for ablative refractive surgery for low myopic astigmatism in eyes with low central corneal thickness.     

Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy

PURPOSE: To evaluate the results of the prophylactic use of mitomycin-C to inhibit haze formation after excimer laser photorefractive keratectomy (PRK) for medium and high myopia in eyes that were not good candidates for laser in situ keratomileusis (LASIK). SETTING: Carones Ophthalmology Center, Milan, Italy. METHODS: This prospective randomized masked study comprised 60 consecutive eyes (60 patients). The inclusion criteria were a spherical equivalent correction between -6.00 and -10.00 diopters (D) and inadequate corneal thickness to allow a LASIK procedure with a residual stromal thickness of more than 250 microm. The eyes were divided into 2 groups according to the randomization protocol. After PRK, the study group eyes were treated with a single intraoperative dose of mitomycin-C (0.2 mg/mL), applied topically with a soaked microsponge placed over the ablated area and maintained for 2 minutes. The control eyes did not receive this treatment. Refraction, uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), and slitlamp evidence of corneal opacity (haze) or other visible complications were evaluated. RESULTS: No toxic or side effects were encountered postoperatively. No study group eye had a haze rate higher than 1 during the 6-month follow-up; 19 eyes (63%) in the control group did (P =.01). At 6 months, the between-group difference in the refractive outcome was statistically significant (P =.05), with 26 study group eyes (87%) and 14 control eyes (47%) within +/-0.50 D of the attempted correction. No study group eye had a BCVA loss during the follow-up; 7 control eyes had lost 1 to 3 lines at 6 months (P =.0006). CONCLUSIONS: The prophylactic use of a diluted mitomycin-C 0.02% solution applied intraoperatively in a single dose after PRK produced lower haze rates, better UCVA and BCVA results, and more accurate refractive outcomes than those achieved in the control group.     

Reproducibility of LASIK flap thickness using the Hansatome microkeratome

PURPOSE: To evaluate the actual versus the expected thickness of laser in situ keratomileusis (LASIK) flaps and to determine the factors that affect flap thickness. SETTING: Centre For Sight, Queen Victoria Hospital, East Grinstead, United Kingdom. METHODS: A retrospective analysis of LASIK procedures in 757 consecutive eyes was done. The surgery was performed by a single surgeon using 2 Hansatome microkeratomes (Bausch & Lomb) with 160 microm and 180 microm heads. Patient age, preoperative manifest refraction, automated keratometry, preoperative central pachymetry, and intraoperative stromal pachymetry were evaluated to determine whether they influenced the actual flap thickness. RESULTS: Bilateral LASIK was performed in 343 patients (686 eyes). The 160 microm head was used in 641 eyes (84.6%) (Group 1) and the 180 microm head, in 116 eyes (15.4%) (Group 2). The mean preoperative manifest refraction spherical equivalent (SE) was -3.9 diopters (D) +/- 4.5 (SD) (range +7.4 to -25.0 D) in Group 1 and -4.4 +/- 3.7 D (range +7.1 to -12.9 D) in Group 2. The mean preoperative keratometry reading was 43.6 +/- 1.8 D (range 36.0 to 48.6 D) and 43.6 +/- 1.8 D (range 35.9 to 47.0 D), respectively; the mean preoperative central pachymetry was 543 +/- 35 microm (range 447 to 643 microm) and 548 +/- 31 microm (range 453 to 613 microm), respectively; and the mean flap thickness was 116.4 +/- 19.8 microm and 117.3 +/- 18.0 microm, respectively. The difference between the actual and the expected flap thickness in each group was statistically significant (P<.001). There was no significant difference in the actual flap thickness between the 2 Hansatomes. The preoperative SE and central pachymetry were the only factors that influenced the actual flap thickness (P<.05); thin flaps were more common with increasing myopia and increasing corneal thickness. CONCLUSIONS: Spherical equivalent and preoperative pachymetry were the principal factors that influenced flap thickness. Preoperative keratometry values and patient age did not influence the actual flap thickness.     

Two-stage laser in situ keratomileusis to correct refractive errors after penetrating keratoplasty

PURPOSE: To evaluate the effect of a two-stage laser in situ keratomileusis (LASIK) procedure on eyes with high astigmatism and/or anisometropia after penetrating keratoplasty. METHODS: Eleven postoperative penetrating keratoplasty eyes were included in a prospective, non-controlled study. All patients had at least 4.00 D of astigmatism and/or at least 3.00 D of anisometropia and were spectacle and contact lens intolerant. Two-stage LASIK was performed; in the first stage a hinged corneal flap 160 microm in thickness and 9 mm in diameter was created. After stabilization of corneal shape (1 to 3 months after keratotomy), the corneal flap was lifted and laser refractive treatment (second stage) was performed. RESULTS: After the first stage, a statistically significant reduction in refractive astigmatism (P<.01) was recorded. In all eyes but one, best spectacle-corrected visual acuity was maintained or improved after the procedure. Three months after the second stage, refractive astigmatism in 8 of 11 eyes (73%) was within +/- 1.00 D, and spherical equivalent refraction in 9 of 11 eyes (82%) was within +/- 1.00 D of intended correction. Preoperative irregular astigmatism persisted in three patients (3 eyes) who could not be corrected within +/- 1.00 D of refractive astigmatism and/or +/- 1.00 D of intended spherical equivalent refraction. In one eye, an interface infiltrate developed shortly after creation of the flap, and resulted in limited melting. CONCLUSIONS: A two-stage LASIK procedure improved visual acuity and refraction in postoperative penetrating keratoplasty eyes with high astigmatism and/or anisometropia. Complications were uncommon but can lead to loss of vision.     

Topography-controlled excimer laser photorefractive keratectomy

PURPOSE: To assess whether photorefractive keratectomy (PRK) controlled by videokeratography can successfully treat refractive errors in eyes with corneal irregularities and improve spectacle-corrected visual acuity. METHODS: In a prospective clinical study, PRK was performed in 10 eyes of 10 patients. Reason for surgery was irregular astigmatism after penetrating keratoplasty, corneal irregularity after corneal scarring, corneal astigmatism in keratoconus, and decentration after myopic and hyperopic PRK. Excimer ablation was controlled by preoperative videokeratography (Orbscan II, Orbtek) using the MEL-70 system from Aesculap Meditec. Follow-up was 6 months. RESULTS: Concerning manifest refraction, the sphere was reduced on average from +1.92 to +0.57 D, 6 months postoperatively. Cylinder changed from -1.95 D on average to -0.30 D at 6 months postoperatively. There was improvement of uncorrected visual acuity of 2 or more lines in 5 eyes and no change in 5 eyes 6 months postoperatively. Spectacle-corrected visual acuity improved in 2 eyes by 2 to 3 lines, in 9 eyes by 1 to 3 lines, and showed no change in 1 eye. CONCLUSION: Videokeratography-controlled PRK improved refractive errors in irregular corneas with improvement of spectacle-corrected visual acuity.     

Recovery of uncorrected visual acuity after laser in situ keratomileusis or photorefractive keratectomy for low myopia

PURPOSE: To compare uncorrected visual acuity and refractive error in patients undergoing photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) between 1 week and 6 months after surgery. METHODS: All eyes underwent PRK or LASIK with the VisX StarS2 excimer laser. We retrospectively analyzed data from 77 random eyes of 77 patients in the PRK group and 76 eyes of 76 patients in the LASIK group. All eyes had a low myopic refractive error (spherical equivalent range, -0.88 diopters (D) to -5.13 D; mean PRK. -2.8 +/- 0.20 D: LASIK, -2.5 +/- 0.22 D). Uncorrected visual acuity and manifest refractive error were evaluated 1 week, 1 month, and 6 months after surgery. RESULTS: Each eye undergoing PRK was paired with an eye undergoing LASIK for a similar level of spherical equivalent. Mean uncorrected visual acuity after 1 week was 0.85 +/- 0.06 (20/25, logMAR 0.12 +/- 0.04) for the PRK group and 1.01 +/- 0.06 (20/20, logMAR 0.01 +/- 0.03) for the LASIK group (p < 0.001). Mean spherical equivalent after 1 week was 0.23 +/- 0.12 D for the PRK group and -0.02 +/- 0.07 D for the LASIK group (p = 0.02). Mean uncorrected visual acuity after 1 month was 1.03 +/- 0.05 (20/20, logMAR 0.02 +/- 0.03) for the PRK group and 1.05 +/- 0.05 (20/20. -0.02 +/- 0.03) for the LASIK group (p = 0.16). Mean spherical equivalent after I month was 0.19 +/- 0.10 D for the PRK group and -0.02 +/- 0.09 D for the LASIK group. This difference was statistically significant (p = 0.02), but was unlikely to be clinically significant. Mean uncorrected visual acuity after 6 months was 1.05 +/- 0.06 (20/20, logMAR -0.01 +/- 0.03) for the PRK group and 1.06 +/- 0.05 (20/20, logMAR -0.14 +/- 0.03) for the LASIK group (p = 0.41). Mean spherical equivalent after 6 months was 0.02 +/- 0.08 D for the PRK group and 0.00 +/- 0.08 D for the LASIK group (p = 0.35). CONCLUSION: Uncorrected visual acuity 1 week after surgery is significantly better in eyes undergoing LASIK than in eyes undergoing PRK. Both procedures provide functional vision by 1 week after surgery. The difference does not relate to refractive error, which was similar between the two groups, but to differences in healing of the epithelium. By 1 month after surgery, there is no difference in mean uncorrected visual acuity between eyes that undergo PRK or LASIK for low myopia.