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.     

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.     

Ocular surface management of photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To examine the effects of keratorefractive surgery and ocular surface management on goblet cell density, dry eye symptom incidence, and spherical equivalent refraction. METHODS: We performed a retrospective analysis of four myopia groups: Untreated controls (n = 53); PRK (n = 51); LASIK without ocular surface management (n = 56); LASIK with ocular surface management (n = 140). Ocular surface management involved the routine use of non-preserved artificial tears and other lubricants before, during, and after surgery. Lid hygiene procedures, topical anti-inflammatory agents, and punctal plugs were used on indication. Assessments were conducted before and up to 12 months after surgery (right eyes only in patients with both eyes operated, and in the left or right eye in patients with one eye operated). RESULTS: Surgery caused a significant reduction in goblet cell density, with the greatest reduction in the LASIK without ocular surface management group. No significant differences were detected in dry eye symptoms or spherical equivalent refraction between PRK and LASIK without ocular surface management. Ocular surface management significantly minimized LASIK-induced decreases in goblet cell density and was associated with significantly less myopic outcomes at months 1 to 3 and 6 to 9 after LASIK. After surgery (1 to 3 mo), dry eye symptoms were significantly lower in the LASIK with ocular surface management group. In all groups, significant inverse correlations existed between goblet cell density and dry eye symptoms. CONCLUSIONS: Ocular surface management minimized the negative impact of LASIK on goblet cell density and reduced dry eye symptoms. Without ocular surface management, goblet cell density and dry eye symptoms after LASIK were similar to or worse than after PRK.     

LASEK、PRK和LASIK治疗中低度近视的比较

目的对比分析准分子激光上皮下角膜磨镶术(LASEK)、碰光性角膜切削术(PRK)、激光原位角膜磨镶术(LASIK)治疗中低度近视临床疗效。方法LASEK组58例(112眼)随访3-9月,PRK、LASIK组各120眼随访1a以上,观察分析术后疼痛症状,裸眼视力及角膜混浊情况。结果术后1d出现疼痛症状:LASEK组:81眼(72.3％),PRK组120 眼(100.0％),LASIK组13眼(10.8％);术后3d裸眼视力≥0.8:LASEK组24眼(21.4％),PRK组27眼(22.5％),LASIK组113 眼(94.2％);术后3月存在角膜Haze:LASEK组31眼(27.6％)、PRK组94眼(78.3％),LASIK组0眼。结论LASEK后疼痛症状、角膜Haze明显减轻,疗效优于PRK;LASEK与LASIK相比没有角膜瓣相关并发症,早期视力恢复较慢。     

准分子激光角膜切削术与准分子激光原位角膜磨镶术角膜创口愈合的对比实验研究

比较准分子激光角膜切削术(photorefractive keratectomy,PRK)与准分子激光原位角膜磨镶术(1aser in situ keratomileusis,LASIK)后激光对角膜组织的切削效应及角膜的愈合情况,从组织学角度探讨角膜雾状混浊(Haze)及屈光度数回退的成因。方法24只新西兰白兔按预矫屈光度数随机分为-4.00 D组和-8.00 D组,每只兔右眼行PRK,左眼行LASIK。术后10d,1、3及6个月观察Haze情况并验光,每组随机处死3只兔取角膜行光镜、电镜及免疫组化检查,检测胶原Ⅲ、胶原Ⅳ、纤维连结蛋白(fibronectine,FN)及转化生长因子-β(transforming growth factor-β1,TGF-β2)的含量。结果行PRK术的右眼术后出现不同程度的Haze及屈光度数回退,其程度与预矫正屈光度数成正比。行LASIK术的左眼术后除少数角膜瓣周围半环形混浊外,手术区域角膜透明,屈光度数回退较右眼轻。-4.00 D组右眼与左眼术后屈光度数均稳定,-8.00 D组右眼较左眼屈光度数回退明显。右眼术后角膜愈合反应重,恢复慢。6个月时角膜基质仍处于修复阶段。左眼术后除形成角膜上皮栓及对应处基质轻度增生外,手术区域角膜瓣与基质床间界面清晰,无明显增生,角膜基质愈合反应轻、恢复快。术后所有兔眼角膜均有TGF-β1表达及活化,持续时间与角膜愈合时间一致。Haze及屈光度数回退组织学改变为：角膜上皮细胞增生,基底膜不成熟,前基质角膜细胞活化、增殖,新生胶原Ⅲ合成、排列紊乱,细胞外基质FN在角膜上皮下沉积。结论LASIK矫正近视尤其是高度近视优于PRK;角膜伤口愈合特别是基质愈合的反应程度,是。Haze及屈光度数回退的关键;TGF-β1是角膜愈合过程中重要调节因子,可通过介导角膜上皮一基质相互作用,调节胶原Ⅲ及FN的含量,参与瘢痕形成。     

A mathematical model for laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: The purpose of ablation refractive surgery is to remove the refractive error from the inherently asymmetric aspheric cornea. Although the technique is gaining wide acceptance and popularity, some patients are left with irregular corneas. Our objective was to develop a methodology to analyze corneal shape, reduce the shape to arcs, modify the local arc value to the desired new arc value, and render a new continuous Euclidean surface without discontinuity. METHODS: The method to reconstruct the corneal surface consists of importing scanner output elevation data points into a computer-aided design (CAD) application to form the surface model. The corneal arc measurements are derived at 5 degrees increments and centered about the Gauss point of symmetry. Each arc is manipulated to adjust the corresponding arc on the proposed corneal surface to reflect the new arc value, correcting for the refractive error. The method determines the amount of corneal tilt and ablation depth at a given diameter required for the refractive error with a smooth transition zone to the base cornea. RESULTS: The case example is a patient who began with a spherical refraction of -8.75 D and after LASIK was emmetropic, but had irregular astigmatism and 20/30 best spectacle-corrected Snellen visual acuity. The proposed mathematical model compares the achieved surface shape to the mathematically planned surface contour. An enhancement procedure to remove the LASIK-induced corneal irregularity was designed. CONCLUSION: A mathematical technique to plan myopic ablative surgery to make the corneal surface regular and symmetric is proposed.     

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.     

Comparison of wound healing after photorefractive keratectomy and laser in situ keratomileusis in rabbits.

PURPOSE: To evaluate and compare the corneal wound-healing process after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Kangnam St. Mary's Hospital, Seoul, Korea. METHODS: Two surgical procedures, PRK with the VISX Star excimer laser and LASIK with a MicroTech microkeratome, were performed in 24 rabbit eyes. In the PRK group (n = 12 eyes), the rabbit cornea was treated with a 20 microns ablation. In the LASIK group (n = 12 eyes), a 20 microns laser ablation was performed after a 150 microns thick hinged corneal flap had been made. During both procedures, dichlorotriazinyl aminofluorescien (DTAF) dye was applied to the ablated stromal bed; in the LASIK group, the stromal side of the corneal flap was also stained with DTAF to differentiate regenerated collagen from normal stromal tissue. Corneal wound healing was evaluated postoperatively at 1, 4, 8, and 12 weeks using light, electron, and fluorescence microscopy. The amount of regenerated stromal tissue and the number of keratocytes were analyzed by an image-analysis system. RESULTS: In the PRK group, epithelial migration and regeneration were observed in the ablated area without any stromal regeneration 1 week postoperatively. However, newly regenerated, irregularly arranged stromal collagen, with epithelial hyperplasia in the ablated area, was observed 4 to 12 weeks postoperatively by light and fluorescence microscopy. The number of keratocytes in the surgical area was also increased. In ultrastructural observation using an electron microscope, the shape of keratocytes in the ablated area was changed, and the number of rough and smooth endoplasmic reticuli, ribosomes, mitochondria, and electron-dense vesicles in the cytoplasm were increased, suggesting that the cells were activated. In the LASIK group, there was no observed regenerated collagen between the corneal flap and the ablated stromal bed except in the wound margin. Lamellated, parallel collagen fibers in the cornealstroma were not disturbed. However, in the wound margin, corneal epithelial ingrowth between the flap and the stromal bed was observed, as was some regenerated stromal tissue. The amount of regenerated stromal tissue and the number of keratocytes in the wound area were statistically smaller than those in the PRK group (P < .05). Observation by electron microscopy showed no activated keratocytes, unlike in the PRK group. The collagen fibers in the wound area were parallel. CONCLUSION: Stromal wound healing in the LASIK group was minimal compared with that in the PRK group, except in the wound margin. These results may support the clinical findings of less corneal haze in the human cornea after LASIK.     

PRK与LASIK治疗高度近视的实验研究

研究ＰＲＫ与ＬＡＳＩＫ治疗兔眼高度近视的组织病理学损害。方法：对十只新西兰大白兔右眼行ＰＲＫ,左眼行ＬＡＳＩＫ,手术范围－１０．０Ｄ,分别于术后十天、一月、三月、半年随机选取动物摘除双眼,行光镜及电镜检查。结果：ＰＲＫ术后角膜上皮、上皮基底膜、前弹力层、浅层基质发生了损伤,故引起了不同程度的组织病理学损害,一至三月时最为明显,半年时减轻。ＬＡＳＩＫ术后,角膜细胞正常,胶原纤维规则排列,组织病理学损害较轻。结论：ＰＲＫ与ＬＡＳＩＫ矫正高度近视均不会造成长期的组织病理学损害,但从组织学比较而言,ＬＡＳＩＫ是一种更好的选择     

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.     

The safety and efficacy of photorefractive keratectomy after laser in situ keratomileusis

PURPOSE: To determine the safety and efficacy of performing photorefractive keratectomy (PRK) in corneas previously treated with laser in situ keratomileusis (LASIK) surgery. METHODS: Fifteen eyes of 14 patients who had initially received LASIK for the treatment of myopia and compound myopic astigmatism were evaluated. Variables included existence of and/or type of flap complication associated with the original LASIK procedure, refractions before and after (3 and 6 months) PRK, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and the development of complications after PRK such as haze, scarring, double vision, or ghosting. RESULTS: All 15 eyes were available for analysis at 6 months. Eleven eyes had experienced flap complications during the initial LASIK procedure and 4 eyes had experienced complications in the LASIK postoperative period. Characteristics prior to performing PRK included 11 myopic and 4 hyperopic eyes. By 6 months after PRK treatment, 87% of eyes had UCVA > or = 20/40, 53% had > or = 20/25, and 40% had > or = 20/20. All eyes had BSCVA of > or = 20/30, with 73% being > or = 20/20. No eye had lost 2 lines of BSCVA and only 1 eye lost 1 line of BSCVA. Sixty percent of eyes were within 1.0 diopters (D) of emmetropia, and 40% were within 0.5 D of emmetropia. A trend towards undercorrection and surgical induction of astigmatism as confirmed by vector analysis was noted. No eye developed significant haze or scarring. CONCLUSIONS: Photorefractive keratectomy may be a safe procedure to perform in corneas previously treated with LASIK surgery. Results show good reduction of refractive error and improvement of UCVA and BSCVA. A significant undercorrection of astigmatism was attributed to surgically induced astigmatism. Further studies are necessary to determine the long-term safety and stability of outcomes.     

Initial results of photorefractive keratectomy and laser in situ keratomileusis performed by a single surgeon.

PURPOSE: To determine the safety and efficacy of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) early in a surgeon's experience. SETTING: Ophthalmology Department, John A. Moran Eye Center, Salt Lake City, Utah, USA. METHODS: Between October 1995 and April 1997, a retrospective analysis was performed of 200 eyes in 128 patients who had PRK or LASIK with a follow-up of at least 3 months. The mean age was 38.1 years +/- 10.4 (SD) in the PRK group and 42.3 +/- 10.1 years in the LASIK group. There were 36 women and 30 men in the former and 32 women and 30 men in the latter. Photorefractive keratectomy, PRK/astigmatic keratotomy (AK), LASIK, or LASIK/AK was performed with the Summit Omnimed excimer laser. Preoperative evaluation included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), cycloplegic refraction, tonometry, and computerized videokeratography. At 1, 3, and 6 months, UCVA, BSCVA, mean spherical equivalent (SE), astigmatism, corneal haze, subjective vision (day, night, glare, and halo), and complications were measured. RESULTS: Mean SE was 0.16 +/- 0.82 diopter (D) in the PRK group and -0.09 +/- 0.63 D in the LASIK group at 1 month (P < .05), -0.18 +/- 0.66 D and -0.16 +/- 0.58 D, respectively, at 3 months, and -0.33 +/- 0.73 D and -0.09 +/- 0.62 D, respectively, at 6 months. Achieved correction was similar in the 2 groups. Mean BSCVA was 22.8 +/- 6.0 in the PRK group and 22.2 +/- 5.3 in the LASIK group at 1 month, 21.1 +/- 6.0 and 21.1 +/- 3.1, respectively, at 3 months, and 19.8 +/- 3.5 and 22.9 +/- 5.2, respectively, at 6 months (P < .005). Mean surface regularity index was 0.68 +/- 0.40 in the PRK group and 0.86 +/- 0.41 in the LASIK group at 1 month, 0.54 +/- 0.26 and 0.72 +/- 0.37, respectively, at 3 months (P < .05), and 0.49 +/- 0.27 and 0.84 +/- 0.42, respectively, at 6 months. Mean surface asymmetry index was 0.71 +/- 0.43 in the PRK group and 0.55 +/- 0.21 in the LASIK group at 1 month (P < .05), 0.53 +/- 0.24 and 0.51 +/- 0.23, respectively, at 3 months, and 0.46 +/- 0.19 and 0.64 +/- 0.54, respectively, at 6 months. The subjective parameters between the groups were significantly different only at 6 months; patients in the PRK group reported better day and night vision. CONCLUSION: With careful preparation and proper training, PRK and LASIK appear to be safe and efficacious even during the surgeon's early learning phases.     

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.     

Diadenosine polyphosphates after laser in situ keratomileusis and photorefractive keratectomy refractive techniques

Purpose: To study the concentrations of diadenosine polyphosphates in the ocular surface after PRK and LASIK. Methods: Sixty‐one patients (30 males and 31 females) with ages ranging from 20 to 63 (34.04 ± 9.13 years) were recruited in Balear Institute of Ophthalmology, Palma de Mallorca, Spain. LASIK was performed in 92 eyes of 46 patients and PRK in 25 eyes of 15 patients. Variations in the levels of diadenosine polyphosphate (Ap₄A and Ap₅A), Schirmer I (Jones test), TBUT, corneal staining together with the Dry Eye Questionnaire to evaluate discomfort and dryness were studied. All tests were performed at the preoperative visit and at 1‐day, 2‐week, 1‐month and 3‐month postoperative visits. Results: Ap₄A showed a 5 and 3.5 fold increase at the 1‐day visit for LASIK and PRK, respectively. LASIK patients continued having higher statistically significant concentrations (p = 0.01) all over the follow‐up. Ap₅A showed no significant differences at any visit. Tear volume decreased during the 3 months in LASIK. The PRK cases had a normal volume at 1 month. TBUT in LASIK increased at the 1‐day visit (p = 0,002) and decreased from the 2 weeks onwards and for the PRK, decreased by a 35% at the 1‐day visit and kept reduced for a month. Discomfort only increased at the 1‐day visit (p = 0.007). Dryness frequency was similar in all visits. Conclusions: Ap₄A levels only are increased in refractive surgery patients during the first day after the surgery. This increasing suggests that Ap₄A may help accelerating the healing process.     

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.     

Straylight values 1 month after laser in situ keratomileusis and photorefractive keratectomy

PURPOSE: To compare straylight values before and 1 month after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). SETTING: Private practice refractive surgery center, Delft, The Netherlands. METHODS: In a prospective nonrandomized study, straylight values of 21 patients (42 eyes) were measured using the van den Berg straylight meter (third generation) during intake sessions at a refractive surgery clinic. Of the 21 patients, 12 were scheduled for LASIK (6 patients, 12 eyes) or PRK (6 patients, 12 eyes). At the 1-month follow-up visit, straylight values were measured again in the same manner and compared with the preoperative straylight values. RESULTS: Overall, there was no statistically significant increase in straylight values compared with the preoperative values 1 month after LASIK or PRK (P>.05). Individual straylight values increased in some cases, however, and the values correlated well with decreased quality of vision and changes in the eye examination. CONCLUSION: Straylight values 1 month after LASIK or PRK did not increase on average, although individual straylight values increased in some cases.