Variations in corneal wound healing after radial keratotomy: possible insights into mechanisms of clinical complications and refractive effects.

Ultrastructural and histopathologic analysis was performed on three human corneal specimens for variable and complicated refractive outcomes 1-2 years after radial keratotomy. Specimens were obtained immediately postsurgery after microkeratome resection with homoplastic lamellar keratoplasty (two cases) and penetrating keratoplasty (one case) for correction of glare, severe astigmatism, overcorrection, and/or double vision. All three cases showed variability of wound healing and delayed corneal wound healing sites; epithelial retention cysts, and/or absence of stromal scar collagen that was not dependent on the length of time after surgery. Two of the three radial keratotomy specimens also contained extensive duplication of the superficial corneal epithelial basal lamina. When present, the thickened basal lamina (3-6 microns in thickness) was seen between all incisions evaluated and appeared to extend from the central optical zone out to the periphery of the lamellar button. The one full-thickness keratoplasty specimen showed focal loss of underlying endothelial cells with occasional migrating cells seen by scanning electron microscopy. These data support previous findings that delayed corneal wound healing with epithelial retention cysts remains the most common histopathologic alteration after radial keratotomy. The effects of variations and delay in wound healing between individuals could explain the lack of predictability of refractive outcome and continuing refractive instability in long-term follow-up after single or repeat radial keratotomy surgeries.     

Tissue addition theory of radial keratotomy: a geometric model

We examined the use of a geometric model to explain the effects of radial keratotomy (RK) on corneal topography based on wound gape of radial incisions. Histopathologic studies of healed human RK incisions revealed incision gape in Bowman's membrane and anterior stroma, with intervening epithelial ingrowth or fibrous scarring. For six human RK incisions examined centrally, mid-peripherally, and peripherally, the linear separation of the cut ends of Bowman's membrane averaged 0.012 mm, 0.018 mm, and 0.027 mm, respectively. The effect of postoperative corneal flattening of the "addition of tissue" within incisions was mathematically predicted by calculating the effects of inducing radial gape on a spherical shell. The predicted change in corneal curvature agreed closely with data from a human case report. The "tissue addition" theory may partly explain the change in corneal topography following RK and subsequent wound healing.     

Radial keratotomy. II. Role of the myofibroblast in corneal wound contraction.

The cellular mechanism of corneal wound contraction after radial keratotomy (RK) was studied in a feline eye model. A total of 10 cat eyes were evaluated at various times from 0-30 days after surgery. Changes in the distribution of intracellular filamentous actin, nonmuscle myosin, alpha-actinin, surface membrane alpha 5 beta 1 integrin, and extracellular fibronectin were studied using immunofluorescence and laser confocal and electron microscopy. From day 3-7, staining for fibronectin increased along the wound margin. By day 7, keratocytes adjacent to the wound margin showed increased f-actin staining with intense staining for fibronectin compared with normal keratocytes. Myosin and alpha 5 beta 1 integrin expression was very weak at this time; alpha-actinin was not found. By day 14, fibroblasts within the wound formed f-actin microfilament bundles (stress fibers) which colocalized with fibronectin. Wound-healing fibroblasts also stained positively for alpha 5 beta 1 integrin, myosin, and alpha-actinin (the latter two were colocalized). The presence of myosin and alpha-actinin in the wound fibroblasts and the re-organization of f-actin into stress fibers by day 14 correlated with the development of wound contraction. A comparison of the cellular distribution of actin, myosin, and alpha-actinin with alpha 5 beta 1 integrin 14 days after injury suggested that integrin was localized along stress fiber bundles during wound contraction. The data from this study suggest that modulation of wound gape during healing of RK wounds may involve transformation of the corneal keratocyte to a myofibroblast-like cell and the subsequent formation of intracellular stress fibers composed of f-actin, nonmuscle myosin, and alpha-actinin. Based on the colocalization of fibronectin filaments and f-actin filaments and the unique distribution of alpha 5 beta 1 integrin, these findings support the hypothesis that the tension within the wound is generated by the formation of intracellular stress fibers and the interactions between stress fibers and the extracellular matrix, mediated by specific membrane receptor molecules.     

A new in vitro corneal preparation to study epithelial wound healing.

Corneal epithelial wound healing is an important process necessary for maintenance of visual integrity. Corneal epithelial wound healing occurs by cellular migration and proliferation. However, the molecular basis of reepithelialization is not known. To investigate individual molecular contributions to the wound healing process, an in vitro corneal preparation comparable to the in vivo condition is needed. This investigation developed a new whole mount in vitro rabbit cornea preparation and studied epithelial wound healing rates for epithelial and subepithelial wounds. The wound closure rates obtained in this study for epithelial and subepithelial wound healing (52 +/- 14 microns/hr and 38 +/- 7 microns/hr, respectively) are comparable to in vivo rates of wound healing determined by other laboratories for rabbits. This preparation, achieved by functionally separating the epithelial and endothelial sides of the cornea, allows application of agents to the cornea in a manner that approximates the in vivo condition. This in vitro system is promising for future studies designed to investigate corneal wound healing while reducing potential ocular discomfort associated with in vivo corneal wounding.     

A new wound healing model using tissue cultured corneal endothelium. 1. Quantitative study of healing process

A new in vitro model for evaluating endothelial wound healing has been developed. Rabbit and bovine corneal endothelial cells were cultured on coverslips in areas 8mm in diameter with hydroxyethyl methacrylate (HEMA) and monolayer sheets were obtained. Wounds were produced by scraping cells in the center of the cell sheets with a rotating silicone tip. The areas of these wounds were measured with computed planimetry. The average wound area was 3.00 +/- 0.21 mm2 in rabbit cell cultures 3.18 +/- 0.28 mm2 in bovine cell cultures. The healing process after making the wound was observed by inverse phase contrast microscope and wound healing rates were calculated. Wounded areas were covered by 60 hours in rabbit cultures, and by 84 hours in bovine cultures respectively. Wound healing rates during 6-12 and 12-24 hours were 92.5 +/- 11.9 microns 2/h, 62.4 +/- 3.4 microns 2/h in rabbits and 10.6 +/- 3.6 microns 2/h, 62.9 +/- 7.8 microns 2/h in bovine material respectively. The healing rates were higher in rabbit cultures than in bovine cultures. This model can be used for quantitative evaluation of the wound healing process of corneal endothelium.     

Management of the corneal flap in laser in situ keratomileusis after previous radial keratotomy

PURPOSE: To report a method of managing the corneal flap in patients having laser in situ keratomileusis for the treatment of residual refractive errors after radial keratotomy. DESIGN: Retrospective case series. METHODS: Intraoperative dehiscence of radial keratotomy wounds occurred in 7 eyes of 6 patients treated with laser in situ keratomileusis for residual myopia or astigmatism or hyperopia 5 to 15 years after radial keratotomy. To minimize extension of these tears, the flap was initially rolled like a carpet toward the hinge before the ablation and then rolled away from the hinge to its original position after the ablation. RESULTS: Using this method of managing the laser in situ keratomileusis flap in patients with previous radial keratotomy, all eyes had successful laser in situ keratomileusis, with 1-year postoperative uncorrected visual acuity ranging between 20/16 and 20/25. No eye had loss of spectacle-corrected vision or interface epithelial ingrowth. CONCLUSIONS: Laser in situ keratomileusis has proved to be an effective treatment for correction of residual refractive errors after radial keratotomy. The surgical technique used in these cases was targeted at minimizing shearing forces in lifting the corneal flap to avoid extension of radial keratotomy wound dehiscence, which could lead to epithelial ingrowth and loss of best-corrected vision.     

Laser in situ keratomileusis flap margin: wound healing and complications imaged by in vivo confocal microscopy

PURPOSE: To examine the healing response of laser in situ keratomileusis flap margin in vivo. METHODS: Forty-three eyes of 43 patients who had undergone myopic (n = 39) or hyperopic (n = 4) laser in situ keratomileusis were examined once after surgery. The flap margin was imaged by in vivo confocal microscopy at various depths, and the wound healing response, flap alignment, and complications were evaluated. Ten eyes were examined on day 3 postoperatively, 13 eyes at 1 to 2 weeks, 10 eyes at 1 to 2 months, five eyes at 3 months, and five eyes at 6 months or later. RESULTS: At 3 days after laser in situ keratomileusis, the surface epithelium and basal epithelium appeared normal. Keratocyte activation was strongest at 1 to 2 weeks and 1 to 2 months, and an increased amount of haze was observed correspondingly. Intrastromal epithelial cells forming a plug could occasionally be perceived in the wound gape. Wound constriction was completed in most cases by 3 to 6 months or later. Good alignment was observed in 12 of 43 flaps (27.9%) and moderate and poor alignment in 17 of 43 flaps (39.5%) and 13 of 43 flaps (30.2%), respectively. Poor alignment was not associated with lamellar epithelial ingrowth. Epithelial ingrowth was associated with dense haze at the interface. Diffuse lamellar keratitis was imaged in two corneas after hyperopic laser in situ keratomileusis. CONCLUSIONS: The laser in situ keratomileusis incision wound at the flap margin appears to heal after the sequence observed in incisional wounds in nonhuman primates. Complications, such as lamellar epithelial in growth and diffuse lamellar keratitis, were often observed, particularly after hyperopic laser in situ keratomileusis.     

Laser in situ keratomileusis for undercorrection after radial keratotomy.

PURPOSE: To assess the safety and efficacy of excimer laser in situ keratomileusis (LASIK) in treating residual myopia and/or astigmatism following refractive keratotomy. METHODS: Fourteen eyes that had previously undergone radial and/or arcuate keratotomy were included. The surgeries were performed using the Chiron Automated Microkeratome and the VISX 20/20B excimer laser. RESULTS: Average follow-up was 12.64+/-5.02 months. Mean spherical equivalent refraction was reduced from -3.48+/-3.52 D preoperatively to -0.04+/-0.87 D postoperatively. At the last follow-up examination there were 8 eyes (57.1%) with a refraction within+/-0.50 D, and 10 eyes (71.4%) within +/-1.00 D of emmetropia. Uncorrected visual acuity was 20/20 or better in 4 eyes (28.6%) and 20/40 or better in 10 eyes (71.4%). Vector analysis of the astigmatic correction showed an index of success of 80%. There was no significant loss (> or = or =2 lines) of spectacle-corrected visual acuity. We observed interface epithelial ingrowth in one eye. CONCLUSIONS: The correction of residual myopia and/or astigmatism with LASIK in eyes with prior refractive keratotomy proved to be safe and effective. Careful preoperative evaluation may help to avoid complications such as reopening of incisions during surgery or postoperative ingrowth of epithelium beneath the corneal flap.     

Radial keratotomy complicated by sterile keratitis and corneal perforation. Histopathologic case report and review of complications

A 35-year-old physician had radial keratotomy (RK) for correction of myopia. Combined radial and transecting circumferential incisions were used which resulted in wound gape, persistent epithelial defect, and severe sterile keratitis. Progressive corneal decompensation required an initial patch graft followed by a penetrating keratoplasty four months after RK. Histopathology of the cornea demonstrated epithelial edema and persistent incisional epithelial plug formation, deep and superficial vascularization, variable incision depth (superficial to full thickness), endothelial cell loss, and inflammatory cell infiltration at all levels of the cornea. A review of the reported complications of RK is included in the discussion of this case.     

Histopathologic comparison of conventional radial keratotomy and minimally invasive radial keratotomy in rabbits

The aim of the present study was to compare conventional radial keratotomy (RK) with minimally invasive RK (mini-RK) in terms of achieved incisional depth as well as the histopathologic changes in the rabbit corneal structures. Four conventional RK incisions were performed on the right eye and four mini-RK incisions were performed on the left eye of 12 Island rabbits using a centripetal cutting technique. The corneas were excised 20 days after the procedure and examined by light microscopy. Histopathologic examination showed that the mean achieved incisional depth (73.47%) in conventional RK was consistent with the intended incisional depth (80%). However, the mean achieved incisional depth (47.28%) was far from the intended incisional depth (80%) in eyes receiving mini-RK. The difference between achieved incisional depth of the two surgical techniques was statistically significant (t = 10.70, P < 0.05). Corneal structural changes and epithelial plug formations were less in eyes in mini-RK than in conventional RK. These findings suggested that the refractive results in mini-RK may be less effective than conventional RK. On the other hand, in the mini-RK group, less epithelial plug formation and limited histopathologic structural alterations may have an important role in preventing long-term overcorrection and corneal rupture after ocular trauma demonstrated in conventional RK technique.     

Corneal stromal wound healing in refractive surgery: the role of myofibroblasts

While laser and incisional refractive surgery offer the promise to correct visual refractive errors permanently and predictably, variability and complications continue to hinder wide-spread acceptance. To explain variations, recent studies have focused on the role of corneal wound healing in modulating refractive outcomes. As our understanding of the corneal response to refractive surgery broadens, it has become apparent that the response of one cell, the corneal stromal keratocyte, plays a pivotal role in defining the results of refractive surgery. Studies reviewed herein demonstrate that injury-induced activation and transformation of keratocytes to myofibroblasts control the deposition and organization of extracellular matrix in corneal wounds. Myofibroblasts establish an interconnected meshwork of cells and extracellular matrix that deposits new matrix and contracts wounds using a novel and unexpected "shoe-string-like" mechanism. Transformation of keratocytes to myofibroblasts is induced in culture by transforming growth factor beta (TGFbeta) and blocked in vivo by antibodies to TGFbeta. Overall, myofibroblast appearance in corneal wounds is associated with wound contraction and regression following incisional keratotomy and the development of "haze" or increased scattered light following laser photorefractive keratectomy (PRK). By contrast, absence of myofibroblasts is associated with continued widening of wound gape and progressive corneal flattening after incisional procedures. Based on these studies, we have arrived at the inescapable conclusion that a better understanding of the cellular and molecular biology of this one cell is required if refractive surgery is ever to achieve predictable and safe refractive results.     

Slit-lamp microscopic appearance of corneal wound healing after radial keratotomy

Radial keratotomy offers a unique opportunity to study corneal wound healing because the corneas are normal, the fine knife blades disrupt adjacent tissue minimally, no sutures are used, there is minimal inflammation, and few postoperative drugs are administered. We studied corneal wounds with a slit-lamp microscope as they healed from two weeks to three years after radial keratotomy in 84 eyes of 51 consecutive patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) Study. One day after surgery, the incisions were surrounded by edema. At two weeks, a dense, gray, diffusely marginated opacity occupied 0.1 mm on both sides of the incision. At three months, the area adjacent to the incision was filled with discrete, fine, gray spicules that protruded at right angles from the incision. At six months, the gray cloudiness had completely disappeared, and the individual spicules were more prominent. By one year, the spicules were disappearing from the anterior portion of the incision and were concentrated primarily in the posterior part of the incisions. At two and three years, the incision scar was fainter and the spicules had disappeared from all but the deep posterior part of the wound. We believe that these spicules correspond to the reorganization of the stroma along the edges of the corneal incision. The persistence of the spicules suggests that wound healing in radial keratotomy may not be complete until two years or more after surgery.     

In vivo confocal microscopy of epithelial inclusions from aberrant wound healing after astigmatic keratotomy

OBJECTIVE: To report confocal microscopic findings in vivo of delayed prominent epithelial inclusions at a gaped incision groove after astigmatic keratotomy (AK). METHODS: Astigmatic keratotomy using paired arcuate incisions was performed on the right eye of a 59-year-old man who had a preoperative refraction of +2.50 DS, -7.00 DC x 80. The procedure and initial postoperative course were uneventful, and his refraction was OD +1.00 DS, -2.50 DC x 60 at 16 months. However, at 17 months postsurgery, tiny pearl-like lesions appeared along one of the incision grooves. In vivo confocal microscopy was performed to investigate these lesions. RESULTS: Under confocal microscopy, clusters of epithelial inclusions inside the gaped incision groove corresponded to the pearl-like lesions observed clinically. A confluent layer of flat, regular and polygonal epithelial cells covered the wall of the groove. Activated keratocytes were observed adjacently. The number of keratocytes around the groove, however, did not appear to increase in comparison to normal corneal wound healing and scar formation. No foreign body, infective, or inflammatory signs were observed. CONCLUSIONS: Aberrant wound healing was identified in post-AK incisions, similar to post-radial keratotomy cases. Confocal microscopy is a useful tool to study the wound healing of AK incisions and to rule out foreign bodies or infective elements as illustrated by this case. To the best of our knowledge, this is the first reported in vivo confocal study of AK wound healing in humans.     

Corneal sensitivity after photorefractive keratectomy.

Corneal anesthesia or hypesthesia can complicate refractive surgical procedures such as epikeratophakia and radial keratotomy. An esthesiometer was used to measure the corneal sensitivity in unoperated-on corneas and fellow corneas after excimer laser photorefractive keratectomy. Decrease in corneal sensitivity was noted within six postoperative weeks, with mean sensitivity being 75.2% +/- 13.3% of normal. Within the first three postoperative months, the patients operated on for correction of compound astigmatism recovered 95.7% +/- 5.3% of the corneal sensitivity, whereas the patients operated on for correction of severe myopia recovered 86.2% +/- 11.2% (P = .07). None of the patients had delayed epithelial healing or recurrent corneal erosions during the time of decreased corneal sensitivity. In otherwise normal myopic eyes, photorefractive keratectomy measurably reduced corneal sensitivity for several postoperative weeks.     

Intraocular lens power calculation after incisional and thermal keratorefractive surgery

PURPOSE: To evaluate the efficacy of corneal topography in determining the central corneal refractive power in intraocular lens (IOL) power calculations after incisional and thermal keratorefractive surgery. SETTING: Oregon Eye Institute, Eugene, Oregon, USA. METHODS: This retrospective review comprised 20 eyes (14 patients) that had cataract extraction with IOL implantation or refractive lens exchange after radial keratotomy, hexagonal keratotomy, or laser thermal keratoplasty. The effective refractive power (EffRP) of the Holladay Diagnostic Summary on the EyeSys Corneal Analysis System was used to determine the central corneal refractive power, which was input into the Holladay 2 IOL calculation formula. RESULTS: Eighty percent of eyes achieved a postoperative spherical equivalent refraction within +/-0.50 diopter of emmetropia. CONCLUSION: The use of the EffRP increases the likelihood of an acceptable refractive outcome after cataract or refractive lens exchange surgery in eyes with a history of keratorefractive surgery.     

LASEK and photorefractive keratectomy for myopia: clinical and confocal microscopy comparison

PURPOSE: To compare postoperative visual acuity and corneal morphology after laser epithelial keratomileusis (LASEK) versus photorefractive keratectomy (PRK) in the correction of low to moderate myopia. METHODS: In a double-blind, randomized clinical trial, 50 myopic patients (mean: -4.5 +/- 1.35 diopters) were randomized to receive LASEK in one eye and PRK in the fellow eye. No mitomycin C eye drops were used in this study. Patients were observed daily for 4 days, then at 1 month and every 3 months up to 1 year. Uncorrected and best-corrected visual acuity (UCVA and BSCVA), manifest refraction, corneal epithelium healing time, postoperative pain, and corneal haze were evaluated. Corneal wound healing was quantified with corneal confocal microscopy. RESULTS: Refractive error, UCVA, and BSCVA were not statistically different between eyes treated with LASEK and PRK. Corneal epithelium healing time was 2.52 +/- 0.99 days in the eyes treated with PRK and 2.29 +/- 0.52 days in the eyes treated with LASEK (P=.22). The postoperative pain score was 2.17 +/- 0.87 in the eyes treated with PRK and 2.62 +/- 0.60 (P=.02) in the eyes treated with LASEK. Corneal confocal microscopy showed fewer stromal activated keratocytes and less extracellular matrix deposition in the eyes treated with LASEK than in the eyes treated with PRK at 1 month postoperatively (P=.003). CONCLUSIONS: LASEK is an effective and safe procedure for low to moderate myopia, but it seems more painful until full corneal reepithelization. In the early postoperative period, the corneal wound healing process is significantly less intense in eyes treated with LASEK than in eyes treated with PRK. The role of LASEK in corneal wound healing modulation remains controversial.     

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.     

准分子激光治疗性角膜切削术治疗角膜浅层病变的实验和临床研究

目的：观察准分子激光治疗性膜切削术（photo-therapeutic keratectomy,PTK)后兔角膜组织的修复情况,探讨PTK的临床疗效,适应证和治疗参数。方法：（1）实验组采用8．17％硫酸烧灼法制作兔角膜浅层瘢痕模型,2周后行PTK;于术后不同时间进行角膜活体共焦显微镜,神经染色,光镜和透射电镜检查,并与对照组进行比较。（2）根据临床治疗组26例（30只眼）角膜浅层病变患者的病变种类,分别行去除上皮和非去除上皮PTK。观察术后不同时间患者的视力,屈光状态和角膜曲率变化情况,以及角膜雾状混浊（haze)的程度,随访时间6个月。结果：（1）实验组兔角膜切削区PTK术后早期多形 性粒细胞和巨噬细胞浸润。浅基质成纤维细胞增生活跃,新生胶原纤维排列紊乱,疏松;术后6个月趋于正常,组织修复稳定。（2）临床治疗组PTK术后6个月最佳矫正视力与术前比较,21只眼提高,5只眼不变,4只眼下降;其中PTK治疗角膜营养不良和角膜带状变性的效果最佳;术后6个月haze 0级23只眼,0．5级5只眼,1级2只眼,平均远视移动度数＋1．52D。结论：兔角膜PTK术后6个月组织修复趋于稳定;临床PTK治疗角膜浅层病变患者,方法简便,安全,有效,其中以治疗角膜营养不良和角膜带状变性的效果最佳,采用PTK治疗的角膜病变以不超过角膜前1／3厚度为宜。     

In vitro contractility of avascular corneal wounds in rabbit eyes

Contraction of corneal wounds has been the topic of recent speculation, particularly in reference to regression of corneal flattening following radial keratotomy. In an animal model of corneal wound fibroplasia, we offer the first demonstration of in vitro contractility by avascular corneal wound tissue. Three millimeter diameter full-thickness corneal trephine wounds were made in 17 New Zealand white rabbit eyes. The animals were killed and specimens were extracted 3-4 wk postinjury. Contractile responses of corneal wounds were measured on a microdynagauge force transducer. When exposed to serotonin, epinephrine or norepinephrine corneal wounds showed contractions reaching maximum force of 20-100 mg with a peak response obtained within 5-10 min and persisting several hours. Normal corneas did not respond to any agent. All normal iris muscle specimens contracted to acetylcholine exhibiting peak responses of 30-60 mg of force within 5 sec decaying over the following 10-20 min. This is different from corneal wounds which fail to respond to acetylcholine (P less than 0.005). These data suggest that avascular corneal wounds possess contractile properties.     

Scar tissue orientation in unsutured and sutured corneal wound healing.

AIMS--This study aimed to evaluate stromal wound healing morphology in short term unsutured compared with sutured corneal wounds, to define regional variation in healing within radial keratotomy wounds. METHODS--Stromal scar tissue orientation (fibroblast and collagen fibre orientation) was analysed in unsutured and adjacent sutured keratotomy wounds in monkeys, 2 to 9 weeks after surgery, using light and transmission electron microscopy. RESULTS--At 2 to 4 weeks, scar tissue orientation was transverse to the wound edge in unsutured wounds, but sagittal in sutured wounds. At 5 to 9 weeks, a reorientation of scar tissue sagittal to the wound was seen in the unsutured wounds, proceeding from the posterior to anterior wound regions. In sutured wounds, a scar tissue reorientation transverse to the wound was seen, proceeding from the anterior wound region in a posterior direction. CONCLUSIONS--Within the same cornea, sutured and unsutured wounds showed opposite patterns of healing. Sutured wounds initially healed more slowly, but obtained pseudolamellar continuity over time. In contrast, healing of unsutured wounds was characterised by an early approximation towards lamellar repair that was followed by an ineffective reorganisation of the scar. This latter pattern of healing, that may be associated with a variable weakening of the wound, may relate to the clinical findings of unpredictability and/or progression of refractive effect following radial keratotomy.