Corneal epithelial recovery following photorefractive keratectomy

The Effect of Topical Substance-P Plus Insulin-like Growth Factor-1 (IGF-1) on Epithelial Healing After Photorefractive Keratectomy in Rabbits

Purpose

To determine whether topical Substance-P (SP) plus insulin-like growth factor-1 (IGF-1) can improve corneal healing after photorefractive surface ablation in a rabbit.

Methods

After a 9.0-mm corneal de-epithelialization using a combination of chemical (18% alcohol) and mechanical debridement, excimer photorefractive surface ablation was performed bilaterally in eight rabbits (16 eyes) with an 8.0-mm ablation zone and 70-μm depth. The right eye was treated with SP (250 μg/mL) and IGF-1 (25 ng/mL) in hyaluronic acid, one drop twice a day, and the other eye treated with only hyaluronic acid. The epithelial healing process was documented photographically twice a day until healing was complete. Six rabbits were sacrificed 6 weeks after photorefractive keratectomy (PRK) and corneas examined histologically.

Results

Seven of eight rabbit eyes treated with SP/IGF-1 healed in a shorter time than the untreated eye. For rabbit #6, both eyes healed at the same time. The average healing time (total time until wound closure) for the treated eyes was 99 hours, while the average healing time for the untreated eyes was 170 hours (P = 0.0490). A persistent epithelial defect was found in two of the nontreated eyes but none in the treated eyes. Corneal pathology showed some degree of epithelial separation in the central corneal wound in three out of six nontreated eyes and in just the treated eye of rabbit #6.

Conclusion

Topical SP plus IGF-1 increases the epithelial healing rate after PRK. There may have been beneficial effects upon cell adhesion as well.

Translational Relevance

Better and faster healing.

Myofibroblast transdifferentiation: The dark force in ocular wound healing and fibrosis

Wound healing is one of the most complex biological processes to occur in life. Repair of tissue following injury involves dynamic interactions between multiple cell types, growth factors, inflammatory mediators and components of the extracellular matrix (ECM). Aberrant and uncontrolled wound healing leads to a non-functional mass of fibrotic tissue. In the eye, fibrotic disease disrupts the normally transparent ocular tissues resulting in irreversible loss of vision. A common feature in fibrotic eye disease is the transdifferentiation of cells into myofibroblasts that can occur through a process known as epithelial-mesenchymal transition (EMT). Myofibroblasts rapidly produce excessive amounts of ECM and exert tractional forces across the ECM, resulting in the distortion of tissue architecture. Transforming growth factor-beta (TGFβ) plays a major role in myofibroblast transdifferentiation and has been implicated in numerous fibrotic eye diseases including corneal opacification, pterygium, anterior subcapsular cataract, posterior capsular opacification, proliferative vitreoretinopathy, fibrovascular membrane formation associated with proliferative diabetic retinopathy, submacular fibrosis, glaucoma and orbital fibrosis. This review serves to introduce the pathological functions of the myofibroblast in fibrotic eye disease. We also highlight recent developments in elucidating the multiple signaling pathways involved in fibrogenesis that may be exploited in the development of novel anti-fibrotic therapies to reduce ocular morbidity due to scarring.

Examination of the restoration of epithelial barrier function following superficial keratectomy

The goal of the present study was to determine the rate of restoration of the corneal epithelial barrier following a superficial keratectomy using a functional assay of tight junction integrity. Adult Sprague-Dawley rats were anesthetized and a 3-mm superficial keratectomy was performed. The eyes were allowed to heal from 4 h to 8 weeks and the rate of epithelial wound closure was determined. To examine the restoration of the barrier function, EZ-Link Sulfo-NHS-LC-Biotin (LC-Biotin) was applied to all eyes, experimental and control, for 15 min at the time of sacrifice. This compound does not penetrate through intact tight junctions. Indirect immunofluorescence was performed with anti-laminin, a marker of basement membrane; fluorescein-conjugated streptavidin to detect the biotinylated marker; and anti-occludin and anti-ZO-1, markers of tight junctions. Epithelial wound closure was observed at 36-42 h after wounding. LC-Biotin did not penetrate the intact epithelium. Upon wounding, LC-Biotin penetrated into the stroma subjacent and slightly peripheral to the wound area. This pattern was present from 4-48 h post-wounding. The area of LC-Biotin localization decreased with time and the functional barrier was restored by 72 h. Occludin and ZO-1 were present at all time points. The number of cell layers expressing these proteins appeared to increase at 48 and 72 h. Continuous laminin localization was not observed until at least 7 days after wounding. Barrier function is restored within 1-1.5 days after epithelial wound closure. The loss of barrier function does not extend beyond the edge of the original wound. The restoration of barrier function does not appear to correlate with reassembly of the basement membrane in this model.

Pupil response to tropicamide following laser in situ keratomileusis

PURPOSE

To investigate the effect of corneal thinning after laser in situ keratomileusis (LASIK) on the corneal penetration of topical eye medication.

SETTING

Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.

METHODS

Laser in situ keratomileusis surgery was performed in 19 eyes of 10 patients enrolled in this prospective study. Measurements were made before surgery and 3 months postoperatively. After instillation of tropicamide 1%, the change in pupil size over time was measured with a Colvard pupillometer. Central corneal thickness (CCT) was measured with ultrasonic pachymetry before and 3 months after LASIK. The corneal epithelial condition was also examined by fluorescein dye staining.

RESULTS

The mean CCT decreased significantly from 564 microm +/- 33 (SD) before LASIK surgery to 514 +/- 48 microm 3 months postoperatively (P<.0001). Pupil diameter 10, 15, and 20 minutes after tropicamide 1% instillation was significantly larger 3 months after surgery than preoperatively (P=.0083, P=.0043, and P=.0144, respectively). The mean time to reach a pupil diameter of 6.0 mm decreased significantly from 14.4 +/- 4.3 minutes in preoperative eyes to 11.5 +/- 2.3 minutes in postoperative eyes (P=.0281). Mild punctate corneal epithelial staining (fewer than 5 spots) were observed in 4 eyes at the 3-month postoperative examination.

CONCLUSIONS

Pupil dilation after tropicamide 1% instillation was significantly faster after LASIK surgery. Corneal thinning that resulted from LASIK enhanced corneal penetration of tropicamide 1%.

Interaction between injured corneal epithelial cells and stromal cells

PURPOSE

To review the effects of injured corneal epithelial cells on myofibroblastic cell formation in corneal stroma after excimer laser surgery.

METHODS

Denudation of epithelium alone, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and LASIK with denudation of epithelium were performed in rabbit eyes. Postoperative anterior stromal haze was assessed using a standard scale. Immunohistochemical methods were used to detect alpha-smooth muscle actin (alpha-SMA), a marker of myofibroblastic cells, and type III collagen in subepithelial corneal tissue. Rabbit corneal fibroblasts were cultured on collagen gels with or without cocultured corneal epithelial cells, or with partially scraped epithelial cells, on a companion plate separated by a permeable membrane. Gel thickness was measured daily to evaluate fibroblast-induced gel contraction. The total number of fibroblasts per gel was determined. Myofibroblasts were counted using immunocytochemical identification with alpha-SMA. Transforming growth factor (TGF)-beta was assayed in media on days 3 and 6; these procedures were also carried out in the presence of anti-TGF-beta antibody.

RESULTS

Three weeks after surgery, the presence of alpha-SMA-positive long-extended and spindle-shaped stromal cells as well as synthesis of type III collagen were observed in the subepithelial stromal layer, corresponding to corneal haze, in eyes that underwent PRK and LASIK with denudation of epithelium, but not in those that underwent denudation of epithelium alone or LASIK. Gel contraction, number of alpha-SMA-positive cells, and total cell number were significantly greater on gels with injured epithelial cells than on those without epithelial cells or with uninjured epithelial cells, as was TGF-beta concentration in media. Anti-TGF-beta antibody eliminated these differences.

CONCLUSIONS

The intact corneal epithelium might play an important role in curbing differentiation of myofibroblasts in corneal wound healing. Injured epithelial cells stimulate fibroblast myodifferentiation through one or more soluble factors, including TGF-beta.

Diffuse Lamellar Keratitis and Flap Margin Epithelial Healing After Laser in situ Keratomileusis

PURPOSE

To evaluate whether wound healing of the corneal epithelium at the flap margin influences development of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK).

METHODS

We examined prospectively 1928 eyes of 994 patients after LASIK. Condition of wound healing at the flap margin 1 day after LASIK was graded as gutter score from 0 to 3, according to the extent of fluorescein staining. Existence of DLK, gutter score, and the location of DLK and gutter were evaluated.

RESULTS

Sixty-eight eyes (3.5%) developed DLK. The average gutter score was significantly higher in patients with DLK compared to those without DLK (P<.001). The location of DLK was identical to the location of gutter in 44 eyes (77.2%).

CONCLUSION

Disruption of integrity of the epithelial barrier function at the flap margin was associcated with diffuse lamellar keratitis after laser in situ keratomileusis.

A review of the development of a synthetic corneal onlay for refractive correction

A synthetic corneal onlay, or implantable contact lens, could obviate the need for spectacles or conventional contact lenses in patients who seek convenient, reversible correction of refractive error. Several research groups have attempted to develop such a product in the past but much of the data from these studies remains unpublished due to commercial interests. This article reviews relevant papers and patents in the corneal implant field and discusses our efforts to develop a synthetic corneal onlay using a perfluoropolyether-based polymer.

Phototherapeutic Keratectomy in Patients With Recurrent Corneal Epithelial Erosions

PURPOSE

To evaluate the outcome of phototherapeutic keratectomy (PTK) in the management of recurrent corneal erosions, refractory to other forms of treatment.

METHODS

Phototherapeutic keratectomy was performed on 43 eyes of 41 patients with recurrent corneal erosions. The corneal epithelium was debrided, and laser ablation was performed to a depth of 6 microm with an ablation zone of 7 to 9 mm, using the Technolas Keracor 117C PlanoScan excimer laser. Follow-up time was 12 to 48 months (mean, 23.3+/-9.1 mo).

RESULTS

After PTK, patients were free of symptoms in 31 eyes (72.1%), and eight eyes (18.6%) had occasional mild symptoms of irritation and photophobia upon awakening. Recurrence of painful corneal erosions occurred in four eyes (9.3%). After PTK retreatment, these patients did not report any further episodes and were free of symptoms for 12 to 30 months (mean, 21.0+/-7.7 mo). The mean spherical equivalent manifest refraction was changed by +0.15+/-0.39 D in the hyperopic direction at 1 year after PTK. Thirty-three eyes (76.7%) were within +/-1 line of preoperative best spectacle-corrected visual acuity (BSCVA). BSCVA was improved by two or more lines in 10 eyes (23.3%). There were no significant complications.

CONCLUSION

Excimer laser PTK with the Technolas Keracor 117C excimer laser was a safe and effective procedure for the treatment of recurrent corneal erosions. Excimer laser PTK can also be useful in improving the visual acuity in these patients. A small percentage of patients may require a second PTK to prevent further episodes of corneal erosions.

Intact corneal epithelium is essential for the prevention of stromal haze after laser assisted in situ keratomileusis

AIMS

To determine the effect of intact corneal epithelium on stromal haze and myofibroblast cell formation after excimer laser surgery.

METHODS

Denuded epithelium alone, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), or LASIK with denuded epithelium was performed in rabbit eyes. Postoperative anterior stromal haze was assessed employing a standard scale. Immunohistochemical methods were used to detect alpha smooth muscle actin (alpha-SMA), a marker for myofibroblastic cells, and type III collagen in subepithelial corneal tissue.

RESULTS

Three weeks after surgery, the presence of alpha-SMA positive long extended and spindle-shaped stromal cells, and synthesis of type III collagen were observed in the subepithelial stromal layer corresponding to corneal haze in PRK and LASIK with denuded epithelium, but not in denuded epithelium alone and LASIK.

CONCLUSION

The intact corneal epithelium may play an important part curbing subepithelial haze and differentiation of myofibroblasts in corneal wound healing.

Changes in corneal epithelial barrier function after excimer laser photorefractive keratectomy

PURPOSE

To use fluorophotometry to measure corneal epithelial barrier function after excimer laser photorefractive keratectomy (PRK).

SETTING

Seoul National University Hospital, Seoul, Korea.

METHODS

Twenty-five eyes of 21 patients (13 women, 8 men) had PRK to correct myopia. Corneal epithelial healing time was measured and corneal epithelial permeability to sodium fluorescein evaluated by fluorophotometry 1, 2, and 3 weeks after surgery.

RESULTS

Epithelial permeability showed a statistically significant increase 1 week after surgery and returned to its preoperative level 1 week later. Comparative studies according to epithelial healing day and corrected diopter showed results that were not statistically significant (P > .05).

CONCLUSION

These results suggest that PRK delays complete reconstruction of corneal epithelial barrier function. In humans, the corneal epithelium regained its normal barrier function 2 weeks after PRK. Thus, at least during these weeks, care should be taken to minimize further epithelial trauma.

Real-time confocal microscopic observations on human corneal nerves and wound healing after excimer laser photorefractive keratectomy

PURPOSE

Corneal wound healing after excimer laser photorefractive keratectomy (PRK) passes through a series of characteristic stages which have earlier been defined by means of histological, histochemical, and biochemical approaches. We investigated the potential of confocal microscopy to verify morphological changes in human corneas in vivo after PRK.

METHODS

Ten corneas of eight patients that had earlier undergone PRK were examined at different postoperative time points (7 days-34 months). One of the PRK patients was examined sequentially three times. Three additional corneas, which had earlier undergone corneal grafting surgery and then were subjected to excimer laser photoastigmatic keratectomy (PARK), were studied as well. Seven healthy untreated corneas served as controls to define the normal morphology of human cornea. A tandem scanning confocal microscope (TSCM) was used to generate real-time images of the corneas on an S-VHS videotape. The images were either digitized and further processed or the individual video frames were produced with a video printer.

RESULTS

Seven days post-PRK in vivo confocal microscopy revealed the presence of morphologically immature surface epithelial cells. Delicate nerves, activated keratocytes and deposition of extracellular light-reflecting scar tissue were perceived. The epithelium appeared normal one month post-PRK. Ongoing activation of the anterior stromal keratocytes along with extracellular scar tissue were detected. We also observed increasing numbers of regenerating subepithelial nerve leashes with somewhat twisted pattern. Highly reflective, presumably activated keratocytes were no longer detected 6-7 months post-PRK. Hypercellularity with scar tissue could still be found up to 30 months post-PRK. Only one cornea examined 34 months post-PRK showed normal keratocyte morphology and recovery of the anterior stroma. However, the morphology of subepithelial nerves was still somewhat abnormal. The two corneal grafts examined 11 or 32 months post-PARK exhibited a normal-appearing epithelium but considerable stromal hypercellularity and extracellular scar deposition. The subepithelial nerves were poorly regenerated in one eye and fairly well detectable in the other. The third graft examined 15 months post-PARK revealed the presence of enlarged surface epithelial cells and dense stromal scarring but no nerves.

CONCLUSION

TSCM clinically confirms the earlier histological data on healing of excimer laser wounds. It offers a distinct improvement in the assessment of excimer laser-treated corneas, as it enables cellular details and nerves to be perceived in vivo. In addition the thickness of the stromal scar can be be measured for e.g. planning of phototherapeutic keratectomy.