Corneal sensation after correction of myopia by photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To compare the effects of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on corneal sensation. SETTING: Ohshima Hospital of Ophthalmology, Fukuoka, Japan. METHODS: Corneal sensation was measured with a Cochet-Bonnet esthesiometer in 35 patients before and 3 days, 1 week, and 1 and 3 months after correction of myopia by PRK (22 patients) or LASIK (13 patients). RESULTS: After PRK, corneal sensitivity was decreased slightly at 3 days, began to recover at 1 week, and returned to preoperative values at 3 months; none of the changes was statistically significant (P >.05). After LASIK, corneal sensation was significantly decreased at 3 days, 1 week, and 1 month; it recovered slightly at 3 months, although it remained significantly less than preoperatively. CONCLUSIONS: Laser in situ keratomileusis was associated with a negative effect on corneal sensation, which was markedly greater than the effect with PRK and was evident for at least 3 months after surgery.     

准分子激光屈光性角膜术对泪膜稳定性的影响

目的：研究准分子激光屈光性角膜术（ＰＲＫ与ＬＡＳＩＫ）前后泪膜的变化。方法：选择８７ 眼近视眼患者分两组进行ＰＲＫ和ＬＡＳＩＫ术,分别观察患眼术前和术后３ 天、１０ 天、１ 月、３ 月及６ 月（ＬＡＳＩＫ组未查） 的主观感觉、上皮缺损情况、泪膜形态、非侵犯性泪膜破裂时间（ＮＩＢＵＴ） 和侵犯性泪膜破裂时间（ＢＵＴ） ,并对结果作统计学分析。结果：①ＰＲＫ 组有１８ 眼感觉较术前干燥,ＬＡＳＩＫ 组无一例出现症状,两组相比有显著性差异（ Ｐ＜ ０ ．０１） 。②术后３ 天、１０ 天ＰＲＫ组术后上皮缺损者明显多于ＬＡＳＩＫ组,两组相比有显著性差异（ Ｐ＜０．０１） 。③两组各眼术前、术后的泪膜形态均无改变。④ＰＲＫ组ＢＵＴ术后３ 天、１０ 天、１ 月较术前明显缩短,有显著性差异（Ｐ＜０．０１）;ＬＡＳＩＫ 组术前、术后各期相比均无显著性差异（ Ｐ＞ ０．０５）。结论：ＰＲＫ可影响泪膜的稳定性,但随着角膜的愈合而逐渐恢复,ＬＡＳＩＫ由于保留了角膜上皮的完整性而不影响其稳定性。角膜上皮层结构的改变是引起泪膜稳定性下降的主要原因。     

Comparison of tear secretion and tear film instability after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To evaluate and compare tear secretion and tear film instability following photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, Yonsei University School of Medicine, Seoul, Korea. METHODS: In a prospective study, 36 eyes (21 patients) had PRK and 39 eyes (25 patients) had LASIK to correct myopia. Tear secretion and tear film instability were tested preoperatively and 3 and 6 months postoperatively using Schirmer test values, tear breakup time (BUT) scores, and tear osmolarity. RESULTS: Six months after surgery, the change in Schirmer test values from preoperative levels was -14.57% +/- 6.39% (SD) in the PRK eyes and -23.40% +/- 5.94% in the LASIK eyes and the change in BUT scores, -12.54% +/- 8.28% and -18.79% +/- 13.01%, respectively. The change in tear osmolarity was 14.95% +/- 6.46% and 35.63% +/- 8.51%, respectively. CONCLUSIONS: The decrease in tear secretion was greater after LASIK than after PRK at 6 months. Proper treatment of dry eye is required after LASIK and PRK, particularly in the LASIK postoperative period.     

Corneal keratocyte deficits after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To measure changes in keratocyte density up to five years after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). DESIGN: Prospective, nonrandomized clinical trial. METHODS: Eighteen eyes of 12 patients received PRK to correct a mean refractive error of -3.73 +/- 1.30 diopters, and 17 eyes of 11 patients received LASIK to correct a mean refractive error of -6.56 +/- 2.44 diopters. Corneas were examined by using confocal microscopy before and six months, one year, two years, three years, and five years after the procedures. Keratocyte densities were determined in five stromal layers in PRK patients and in six stromal layers in LASIK patients. Differences between preoperative and postoperative cell densities were compared by using paired t tests with Bonferroni correction for five comparisons. RESULTS: After PRK, keratocyte density in the anterior stroma decreased by 40%, 42%, 45%, and 47% at six months, two years, three years, and five years, respectively (P < .001). At five years, keratocyte density decreased by 20% to 24% in the posterior stroma (P < .05). After LASIK, keratocyte density in the stromal flap decreased by 22% at six months (P < .02) and 37% at five years (P < .001). Keratocyte density in the anterior retroablation zone decreased by 18% (P < .001) at one year and 42% (P < .001) at five years. At five years, keratocyte density decreased by 19% to 22% (P < .05) in the posterior stroma. CONCLUSIONS: Keratocyte density decreases for at least five years in the anterior stroma after PRK and in the stromal flap and the retroablation zone after LASIK.     

Corneal sensation after laser in situ keratomileusis

PURPOSE: To report the time course for the return of corneal sensation following laser in situ keratomileusis (LASIK). SETTING: University-based retractive surgery practice. METHODS: Twenty-eight eyes of 18 patients having LASIK were evaluated. Preoperative and postoperative corneal sensation at the nasal flap hinge, at the central cornea, and within the temporal flap edge were measured before and after LASIK for a 3 week period using the Cochet-Bonnet esthesiometer (Luneau). RESULTS: Corneal sensation initially decreased in all 3 positions of the flap measured after LASIK; the greatest decrease was in the central cornea. Near preoperative corneal sensation returned by 3 weeks. The degree of sensation loss did not appear to correlate with the ablation depth. CONCLUSION: Corneal sensation is significantly decreased for approximately 2 to 3 weeks after LASIK, centrally greater than nasally at the flap hinge or temporally within the flap edge, but it generally returns to near the preoperative level by 3 weeks postoperatively.     

Changes in central corneal thickness after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To evaluate changes in corneal thickness after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) in eyes with the same preoperative refraction, correlate these changes to postoperative refractive outcomes, and compare corneal healing process in a standardized subset of patients. METHODS: Central corneal thickness was measured by contact ultrasound pachymetry in 14 eyes of 8 patients with preoperative myopia of -6.00 D who had LASIK, and in 14 eyes of 8 patients with the same preoperative refractive error who had PRK. Measurements were taken preoperatively, and 1 week, 3, and 6 months after surgery. Data were evaluated and compared using the paired Student t-test and Pearson correlation coefficient. RESULTS: Mean preoperative central corneal thickness in the LASIK group was 549.14 +/- 37.4 microm, and in the PRK group, 552.64 +/- 34.9 microm. At 1-week postoperatively, mean central corneal thickness in the LASIK eyes was 467.28 +/- 29 microm and in the PRK eyes, 473.85 +/- 39.2 microm; at 6 months, central corneal thickness had increased in both groups compared to the 1-week values; LASIK eyes had a mean central corneal thickness of 481.42 +/- 23.0 microm and PRK, 481.50 +/- 35.3 microm. Mean postoperative refraction after 6 months was -0.48 +/- 0.30 D in the LASIK group and -0.67 +/- 0.35 D in the PRK group. CONCLUSION: Increase in central corneal thickness between 1 week and 6 months postoperatively occurred in both LASIK and PRK eyes, but differences were not statistically significant. No statistically significant differences were found in myopic regression between the two patient groups.     

Intacs after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To evaluate the efficacy of intrastromal corneal ring segments (Intacs, Addition Technology) for the correction of residual myopia after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). METHODS: In this prospective noncomparative case series, Intacs were implanted in 5 eyes (4 patients) that developed myopic regression after LASIK or PRK. Intacs were implanted a minimum of 11 months after the laser procedure. The technique was identical to the standard procedure for myopic unoperated eyes. The Intacs thickness was based on the amount of residual myopia. RESULTS: Postoperative results revealed a reduction in the residual myopia and the mean K-reading. No eye lost best corrected Snellen visual acuity. No intraoperative or postoperative complications occurred. CONCLUSIONS: Implantation of Intacs in eyes with myopic regression after LASIK and PRK resulted in a good refractive outcome and an improvement in uncorrected visual acuity.     

Corneal sensitivity after photorefractive keratectomy and laser in situ keratomileusis for low myopia.

PURPOSE: To evaluate and compare the recovery of postoperative corneal sensitivity after laser in situ keratomileusis and photorefractive keratectomy for the correction of low myopia. METHODS: In a prospective study, 17 consecutive eyes (17 patients) underwent laser in situ keratomileusis to correct myopia ranging from -3.25 to -6.75 diopters, and another 18 consecutive eyes (18 patients) underwent photorefractive keratectomy to correct myopia from -3.12 to -7.00 diopters. Corneal sensitivity was tested preoperatively and 1 week and 1, 3, and 6 months postoperatively using the Cochet-Bonnet esthesiometer. Corneal sensitivity was tested at the center of the cornea, and in four additional central points 2 mm from the corneal center (nasal, inferior, temporal, and superior). RESULTS: Corneal sensitivity after laser in situ keratomileusis was reduced at the ablated zone during the first 3 months after surgery (Wilcoxon rank sum test, P < .05), and only after 6 months it returned to its preoperative values. However, corneal sensitivity recovered its preoperative values 1 month after photorefractive keratectomy (Wilcoxon rank sum test, P > .05), except for the central corneal point, where 3 months were required. Comparing both groups, corneal sensitivity was more depressed after laser in situ keratomileusis than after photorefractive keratectomy during the first 3 months (Mann-Whitney test, P < .05), except for the nasal central point, although no differences were found between both groups at 6 months (P > .05). CONCLUSIONS: In the correction of low myopia, corneal sensitivity at the ablated zone was more depressed after laser in situ keratomileusis than after photorefractive keratectomy during the first 3 months after surgery. Only after 6 months were corneal sensitivity values similar in both groups.     

Macular hole after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To describe three myopic patients who developed unilateral macular hole after undergoing bilateral laser in situ keratomileusis or photorefractive keratectomy. METHODS: Case reports. RESULTS: Three eyes of three myopic patients developed a macular hole in one eye after bilateral laser in situ keratomileusis or photorefractive keratectomy. The macular hole formed between 4 to 7 weeks after laser in situ keratomileusis in case 1 (a 48-year-old woman), and within 2 months after laser in situ keratomileusis in case 2 (a 36-year-old woman). In case 3 (a 45-year-old man), the macular hole was found 9 months after photorefractive keratectomy. A vitrectomy closed the macular hole of case 1 with final best-corrected visual acuity of 20/25 and case 2 with 20/30, whereas case 3 declined further surgery. CONCLUSION: A macular hole may develop in myopic eyes after laser in situ keratomileusis or photorefractive keratectomy. Vitreoretinal interface changes may play a role.     

准分子激光屈光性角膜切削术及原位角膜磨镶术病人的视觉对比敏感度的测定

对准分子激光屈光性角膜切削术及原位角膜磨镶术病人手术前后的视觉对比敏感度及激光干涉视力进行测定。结果表明两组病人手术前后的视觉对比敏感度及激光干涉视力均无显著性差异。在手术中,准分子激光切削时的冲击力及负压吸引,对视网膜的功能无显著性影响     

Changes in tear flow and tear film stability after photorefractive keratectomy.

PURPOSE: To investigate the changes in tear flow and tear film stability after photorefractive keratectomy (PRK) for myopia. MATERIAL AND METHOD: One eye of 32 patients underwent unilateral PRK procedure for the correction of myopia ranging from -1.50 to -6.00 diopters (D) (mean -3.65 +/- 1.55 D). Schirmer test values and break-up time (BUT) scores were measured 6 weeks after the PRK procedure. Unoperated, contralateral eyes were used as control eyes for each patient. The Schirmer test scores and BUT values were statistically analyzed using independent t test. RESULTS: The mean Schirmer test value was 14.45 +/- 7.79 mm in the operated eyes. It was 28.83 +/- 5.89 in the control eyes. The decrease in Schirmer test value was statistically significant (t = 8.28, p = 0.0001). The mean BUT scores were 13.19 +/- 5.09 s in the operated eyes and 27.83 +/- 9.31 s in the control eyes. The decrease was statistically significant (t = 7.86, p = 0.0001). CONCLUSION: PRK causes a decrease in tear flow and tear film stability that is probably caused by decreased corneal sensation after PRK.     

Corneal sensitivity and some properties of the tear film after laser in situ keratomileusis

PURPOSE: To investigate central corneal sensitivity, lipid layer structure of the precorneal tear film, and tear volume after laser in situ keratomileusis (LASIK). METHODS: Central corneal sensitivity was measured using the Non-Contact Corneal Aesthesiometer. The aesthesiometer was mounted on a slit lamp and an airpulse of controlled pressure was directed onto the cornea. When central corneal sensitivity was reduced, a higher air pulse pressure was required to stimulate the cornea. The final central corneal sensitivity threshold measured was recorded in millibars. Tear lipid layer structure was assessed by optical interferometry and classified according to appearance using the Keeler Tearscope. Tear volume was measured using the phenol red cotton thread test. Subjects were recruited from a group of patients after LASIK who had experienced no complications (n=22). The average postoperative time was 14 weeks and measurements were taken on one eye. In bilateral cases, measurements were recorded from the right eye only. Average attempted correction was -6.30 D (range, -2 to -11 D). Age-matched controls were later recruited for central corneal sensitivity threshold (n=24). A second group of age-matched controls were recruited for tear volume and lipid layer structure (n=24). RESULTS: The median (range) was 1.1 mbars (0.2 to 4.3 mbars) after LASIK and 0.58 mbars (0.20 to 1.3 mbars) in the controls; the difference was statistically significant (P = .043). The lipid layer of the tear film tended to be thinner in eyes after LASIK compared with controls (P = .032). The mean (+/- SD) tear volume was 16.9 +/- 8.3 mm after LASIK and 19.8 +/- 7.1 mm in controls. This difference was not statistically significant (P = .492). CONCLUSION: At 14 weeks postoperatively, central corneal sensitivity was below normal levels and the tear lipid layer was thinner. The poorer quality lipid layer may predispose to symptoms of dry eye after LASIK.     

Ascorbic acid levels in human tears after photorefractive keratectomy, transepithelial photorefractive keratectomy, and laser in situ keratomileusis

PURPOSE: To investigate the level of ascorbic acid in human tear fluid after photorefractive keratectomy (PRK), transepithelial PRK, and laser in situ keratomileusis (LASIK). SETTING: Departments of Ophthalmology and Biochemistry, School of Medicine, Gazi University, Ankara, Turkey. METHODS: Twenty patients (7 women and 13 men) were included in this study. Traditional PRK with epithelial scraping by a blunt spatula followed by surface ablation (7 eyes), transepithelial PRK (7 eyes), or LASIK (6 eyes) was performed. Tears were collected preoperatively and 1 and 5 days postoperatively. Ascorbic acid levels were measured using 2-4 dinitrophenylhydrazine. RESULTS: Ascorbic acid levels in the tear fluid were decreased significantly 1 day after PRK, transepithelial PRK, and LASIK (P <.05). On the fifth day, the ascorbic acid levels were significantly lower than preoperatively in all groups. CONCLUSION: After PRK, transepithelial PRK, and LASIK, the ascorbic acid levels of the tear fluid decreased significantly. Because ascorbic acid is the major scavenger of superoxide radicals in tears, topical ascorbic acid therapy may help eliminate the harmful effect of free radicals from excimer laser surgery.     

Evaluation of the tear film stability after laser in situ keratomileusis using the tear film stability analysis system

PURPOSE: To evaluate the tear film stability of patients before and after laser in situ keratomileusis (LASIK) using the tear film stability analysis system (TSAS). DESIGN: Prospective observational case series. METHODS: New videokeratography software for a topographic modeling system (TMS-2N) was developed that can automatically capture consecutive corneal surface images every second for 10 seconds. Thirty-four subjects (64 eyes) who underwent myopia LASIK were enrolled in this study. All subjects were examined with the new system before LASIK and at 1 week, 1 month, 3 months, and 6 months after the surgery. Corneal topographs were analyzed for tear breakup time (TMS breakup time) and breakup area (TMS breakup area). Based on pre-LASIK TSAS analysis, subjects were separated into normal and abnormal TSAS value groups. The criteria for the normal group were either TMS breakup time more than 5 seconds or TMS breakup area less than 0.2. The percentage of the occurrence of superficial punctuate keratitis was compared between the two groups with regard to subject's dry eye signs and symptoms. RESULTS: Tear film stability decreased significantly during the early period after LASIK, as indexed by decreased TMS breakup time and increased TMS breakup area. Tear film instability resolved at 6 months after surgery. Before LASIK, 22 subjects (43 eyes) had normal TSAS evaluation and 12 subjects (21 eyes) were abnormal. After LASIK, among normal TSAS value eyes, 8 of 43 (18.6%) eyes developed superficial punctuate keratitis. In sharp contrast, 14 of 21 (66.7%) eyes in the abnormal group displayed superficial punctuate keratitis, correlating well with the patients' dry eye symptoms. The difference in the presence of superficial punctuate keratitis after LASIK between normal and abnormal TSAS value groups was statistically significant (P <.001). Subjects with abnormal TSAS evaluation also displayed resistance to dry eye treatment and had extended period of recovery. CONCLUSIONS: Tear film stability analysis can be a useful means for screening LASIK candidates before surgery and for prognosticating dry eye symptoms thereafter.     

Intraepithelial photorefractive keratectomy for regression after laser in situ keratomileusis.

PurposeTo propose a refractive procedure, intraepithelial photorefractive keratectomy (IE-PRK), to treat regression after laser in situ keratomileusis (LASIK).SettingIMO Instituto de Microcirugı̂a Ocular de Barcelona, Cornea and Refractive Surgery Unit, Autonoma University of Barcelona, Barcelona, Spain; Vall d’Hebron Hospital, Department of Ophthalmology, INSERM, University Hospital, Toulouse, France.MethodsThis open but uncontrolled prospective pilot study assessed the efficacy, predictability, and stability of IE-PRK in 21 eyes of 21 patients who had previous LASIK for myopia or myopic astigmatism with a mean spherical equivalent (SE) refraction of −9.80 diopters ± 2.95 (SD). After LASIK, the eyes regressed to a mean of −1.93 ± 0.82 D. They were retreated with IE-PRK, in which a photoablation was performed directly in the epithelium without damage to Bowman’s membrane. Follow-up was up to 1 year.ResultsEight of the 21 eyes (38%) were emmetropic at 6 months and 11 (52.4%) had a refraction between −0.50 and +0.50 D. Refraction was stable from the second week to the first year, with no significant differences among the mean SEs at 10 days, 6 weeks, and 6 and 12 months.ConclusionThe preliminary results of this small series indicate that IE-PRK appears to be safe, especially in selected cases; 1 line of lost best spectacle-corrected visual acuity occurred in 5% of eyes.     

Expression of cyclooxygenase-2 in corneal cells after photorefractive keratectomy and laser in situ keratomileusis in rabbits

PURPOSE: To compare the expression pattern of cyclooxygenase-2 (COX-2) in rabbit corneal cells after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with the same refractive correction. SETTING: Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan. METHODS: Thirty adult albino rabbits were used in the study. Photorefractive keratectomy or LASIK was performed in 1 eye of each animal for the same refractive correction. Each animal was killed after healing intervals up to 6 months. Paraffin sections of the cornea were processed for immunohistochemistry for COX-2 and NFkappaB (p65). RESULTS: After PRK, the central and peripheral corneal epithelia up-regulated COX-2 at 3 days; the central epithelium was positive at 4 weeks. Central and peripheral epithelia returned to negative 3 months later. After LASIK, the central epithelium on the corneal flap up-regulated COX-2 at 1 and 2 weeks; it returned to negative at 4 weeks. The peripheral epithelium was labeled with the antibody. Keratocytes around the stromal incision between the flap and the stromal bed up-regulated COX-2 and returned to negative at 3 months. COX-1 was not detected immunohistochemically in corneal tissue during the healing intervals after both procedures. Nuclear factor kappaB was detected in the cytoplasm and nuclei of migrating corneal epithelial cells 1 day after PRK, was positive in the cytoplasm at 3 days and negative in cytoplasm and nuclei at week and later. CONCLUSIONS: Migrating injured epithelium expressed COX-2 until week 4 during post-PRK healing. Central uninjured epithelium as well as stromal keratocytes expressed COX-2 from 3 days to 2 weeks after LASIK. Uninjured peripheral epithelium also expressed COX-2 at 4 weeks. Activation of stromal keratocytes may induce expression of COX-2 in overlying uninjured epithelium via the inflammatory cytokine(s)/NFkappaB pathway.     

Ablation centration after active eye-tracker-assisted photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To evaluate the ablation centration after active eye-tracker-assisted photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) and to investigate the effect of surgery, patient, and surgeon on the centration. SETTING: Department of Ophthalmology, China Medical College Hospital, Taichung, Taiwan, Republic of China. METHODS: This retrospective study comprised 177 eyes of 101 patients: 16 eyes had PRK and 161, LASIK. All laser treatments were performed with the aid of an eye tracker. The amount of decentration was analyzed by corneal topography. The factors influencing centration were divided into surgery related (PRK/LASIK), patient related (low/high myopia and effect of learning), and surgeon related (learning curve). RESULTS: The mean decentration was 0.33 mm in PRK eyes and 0.35 mm in LASIK eyes. For the surgery-related factor, there was no significant difference between the PRK and LASIK eyes. For the patient-related factors, centration was better in the second eye (effect of learning) and decentration was more severe in eyes with high myopia (low/high myopia). For the surgeon-related factor, there was no significant difference between eyes that had the first 50 LASIK procedures and those that had the last 50 procedures. CONCLUSIONS: An eye tracker, which makes the laser beam follow the eye's movements, helps to avoid severe decentration. This study showed, however, that an active eye-tracking system alone cannot ensure good centration. Patient cooperation and fixation are important.