Regression and wound Healing after Excimer Laser Prk: A Histopathological Study on Human Corneas

Refractive Effect of Epithelial Remodelling in Myopia after Transepithelial Photorefractive Keratectomy

(1) Introduction: We analysed epithelial changes after the treatment of moderate myopia with transepithelial photorefractive keratectomy. (2) Materials and Methods: We used optical coherence tomography data and analysed changes in the stroma and epithelium after ablation. We aimed to ascertain how much epithelium hyperplasia occurred after TransPRK; for this, we used data from 50 eyes treated with TransPRK with the AMARIS 1050 Hz, with a minimum follow-up of 4 months. (3) Results: The measured epithelial changes corresponded to a less than 0.1 ± 0.2D of spherical effect, less than 0.2 ± 0.2D of astigmatic effect, and less than 0.5 ± 0.2D of comatic effect. (4) Conclusions: The changes in epithelial thickness after aberration-neutral transepithelial photorefractive keratectomy for moderate myopia were very small, indicating a low level of epithelial hyperplasia without resembling a regression-inducing lentoid.

EpiLASIK with Mitomycin C

Purpose

Mitomycin C after photorefractive keratectomy (PRK) is used to reduce the development of haze and regression in higher intended corrections. The aim of this study was to investigate the safety, stability, and efficacy of EpiLASIK with mitomycin C.

Methods

Fifty eyes of 29 patients underwent EpiLASIK with the Gebauer EpiLift microkeratome. The mean preoperative spherical equivalent was −6.89 D (SD ±0.63, range −6.0 to −8.0 D). After the laser ablation, mitomycin C 0.02% was applied for 30 seconds on a sterile filter paper. Preoperatively and 1, 3, 6, and 12 months after surgery, a full ophthalmic examination was performed.

Results

In 42 of 50 eyes, the bandage contact lens was removed at day 3. Twelve months after surgery, 96% of all eyes were within ±1.0 D and 82% were within ±0.5 D of intended correction. Five percent of all patients lost 1 line of best-corrected Snellen visual acuity, 42% were stable, and 56% gained 1 or more lines. In most patients, the cornea was clear during the whole follow-up, and in 10% only trace haze was visible. The uncorrected visual acuity was at least 1.0 in 86% of all patients, and all patients reached 0.5.

Conclusions

EpiLASIK with mitomycin C with higher intended corrections seems to be an effective and safe procedure. With the application of mitomycin C, only minimal haze appears.

Photorefractive keratectomy in the cat eye: biological and optical outcomes

PURPOSE

To quantify optical and biomechanical properties of the feline cornea before and after photorefractive keratectomy (PRK) and assess the relative contribution of different biological factors to refractive outcome.

SETTING

Department of Ophthalmology, University of Rochester, Rochester, New York, USA.

METHODS

Adult cats had 6.0 diopter (D) myopic or 4.0 D hyperopic PRK over 6.0 or 8.0 mm optical zones (OZ). Preoperative and postoperative wavefront aberrations were measured, as were intraocular pressure (IOP), corneal hysteresis, the corneal resistance factor, axial length, corneal thickness, and radii of curvature. Finally, postmortem immunohistochemistry for vimentin and alpha-smooth muscle actin was performed.

RESULTS

Photorefractive keratectomy changed ocular defocus, increased higher-order aberrations, and induced myofibroblast differentiation in cats. However, the intended defocus corrections were only achieved with 8.0 mm OZs. Long-term flattening of the epithelial and stromal surfaces was noted after myopic, but not after hyperopic, PRK. The IOP was unaltered by PRK; however, corneal hysteresis and the corneal resistance factor decreased. Over the ensuing 6 months, ocular aberrations and the IOP remained stable, while central corneal thickness, corneal hysteresis, and the corneal resistance factor increased toward normal levels.

CONCLUSIONS

Cat corneas exhibited optical, histological, and biomechanical reactions to PRK that resembled those previously described in humans, especially when the OZ size was normalized to the total corneal area. However, cats exhibited significant stromal regeneration, causing a return to preoperative corneal thickness, corneal hysteresis and the corneal resistance factor without significant regression of optical changes induced by the surgery. Thus, the principal effects of laser refractive surgery on ocular wavefront aberrations can be achieved despite clear interspecies differences in corneal biology.

Laser Epithelial Keratomileusis for the Correction of Hyperopia Using a 7.0-mm Optical Zone With the Schwind ESIRIS Laser

PURPOSE

To investigate the efficacy of laser epithelial keratomileusis (LASEK) for the correction of hyperopia using a 7.0-mm optical zone and a 9.0-mm total ablation zone diameter with the Schwind ESIRIS flying-spot laser.

METHODS

Forty-seven patients (70 eyes) were treated with a mean preoperative spherical equivalent refraction of +2.32 diopters (D) (range: 0 to +5.00 D). All eyes underwent LASEK using 15% alcohol with a 20-second application.

RESULTS

An intact epithelial flap was obtained in 66 (94%) eyes. In 70 eyes at 12 months, the mean spherical equivalent refraction was +0.09 D (range: -0.75 to +1.00 D) with all (100%) eyes within +/- 1.00 D of the intended correction and 60 (86%) eyes within +/- 0.50 D. In 40 eyes with 24-month follow-up, the refractive correction remained stable after 6 months. Hyperopic cylindrical corrections were attempted in 49 eyes (range: +0.25 to +5.00 D) with vector analysis demonstrating a mean 102% correction at 12 to 24 months. In 60 non-amblyopic eyes, uncorrected visual acuity was > or = 20/20 in 47 (78%) eyes. Thirty-three (47%) eyes gained 1 to 2 lines of Snellen decimal equivalent best spectacle-corrected visual acuity, 30 (43%) eyes showed no change, and 7 (10%) eyes lost 1 line. Eight (11%) eyes at 12 to 24 months had grade +/- 1 of paracentral corneal haze and 57 (81%) had no haze. At 12 months (n = 70), the safety index was 1.06 with an efficacy index of 0.95. Analysis of higher order wavefront aberrations showed no significant changes in root-mean-square values post-operatively, except for a significant reduction of fourth order spherical aberration (P < .05).

CONCLUSIONS

Laser epithelial keratomileusis for hyperopia up to +5.00 D using a 7.0-mm optical zone with the Schwind ESIRIS laser provides excellent refractive and visual outcomes with minimal complications. In eyes followed for 24 months, the refractive correction remained stable after 6 months.

Laser Subepithelial Keratomileusis for the Correction of High Myopia With the Schwind ESIRIS Scanning Spot Laser

PURPOSE

To investigate the efficacy of laser subepithelial keratomileusis (LASEK) for the correction of high myopia with the Schwind ESIRIS scanning spot laser (Schwind eye-tech-solutions Gmbh & Co, Kleinostheim, Germany).

METHODS

Fifty-one patients (76 eyes) were treated with a mean preoperative spherical equivalent refraction of -7.55 diopters (D) (range: -6.0 to -10.75 D). All eyes received a LASEK technique using 15% alcohol with a 20-second application.

RESULTS

An intact epithelial flap was obtained in 73 (96%) eyes. At 1 week, uncorrected visual acuity (UCVA) was > or =20/30 in 53 (70%) eyes and > or =20/60 in all eyes. At 6 months (n=76), the mean SE was +0.08 D (range: -1.00 to +1.875 D) with 73 (96%) eyes within +/-1.0 D of the intended correction and 60 (79%) eyes within +/-0.5 D. At 12 months (n=46), the mean SE was -0.07 D (range: -1.375 to +2.0 D) with 44 (96%) eyes within +/-1.0 D of the intended correction and 37 (80%) eyes within +/-0.5 D. Myopic cylindrical corrections were attempted in 68 eyes (range: -0.25 to -4.25 D) with vector analysis demonstrating a mean 85% correction. At last follow-up, UCVA was > or =20/20 in 47 (62%) eyes, > or =20/25 in 63 (83%) eyes, and > or =20/40 in 75 (99%) eyes. Three (4%) eyes gained two lines of Snellen decimal equivalent best spectacle-corrected visual acuity compared to preoperative levels, 68 (89%) eyes showed no change or gained one line, and 5 (7%) eyes lost one line. None lost more than one line. Only 2 (3%) eyes at 6 to 12 months had more than +1 axial corneal haze and 50 (66%) showed no evidence of haze on slit-lamp examination.

CONCLUSIONS

Laser subepithelial keratomileusis for myopia up to -11.00 D with the Schwind ESIRIS laser provides good refractive and visual outcomes, with acceptable visual recovery and minimal complications.

Effects of topical tranilast on corneal haze after photorefractive keratectomy

PURPOSE

To determine whether topical tranilast might reduce corneal haze through suppression of transforming growth factor (TGF)-beta1 synthesis in keratocyte after photorefractive keratectomy.

SETTING

Department of Ophthalmology, Korea University College of Medicine, Seoul, Republic of Korea.

METHODS

Photorefractive keratectomy was performed on 48 eyes of 28 white rabbits and 24 eyes in a tranilast group were treated with tranilast solution, and the other 24 eyes in control group were treated with saline after laser ablation. The grades of corneal haze at 1, 2, 4, and 8 weeks after surgery were evaluated in 10 eyes of each group for comparison. Immunohistochemistry was performed on 10 eyes of each group, and Western blot analysis was done on 4 eyes of each group for studying TGF-beta1 expression at postoperative day 7.

RESULTS

There was no statistically significant difference in corneal haze between 2 groups from week 1 to week 4 after surgery, but a significant difference was found at week 8 after photorefractive keratectomy (P=.02). The mean number of keratocytes that expressed TGF-beta1 in the tranilast group was 58.3 (+/-17.2), which showed significant difference, compared with that of the control group, 104.5 (+/-23.0) (P<.01). Western blot analysis also revealed that the amount of TGF-beta1 in tranilast group was slightly less than the control group.

CONCLUSIONS

Topical tranilast could reduce corneal haze by suppressing TGF-beta1 expression in keratocytes after photorefractive keratectomy.

Laser-assisted subepithelial keratectomy enhancement of residual myopia after primary myopic LASEK: six-month results in 10 eyes

PURPOSE

To determine whether residual myopia after primary laser-assisted subepithelial keratectomy (LASEK) can be corrected by repeated LASEK and whether this procedure is safe and effective.

SETTING

University Eye Clinic, University of Regensburg, Regensburg, Germany.

METHODS

Laser-assisted subepithelial keratectomy was performed in 10 eyes that had had primary LASEK for myopia. The initial mean spherical equivalent (SE) was -6.2 diopters (D) (range -2.5 to -8.0 D), and the residual mean SE was -1.6 D (range -1.0 to -3.0 D). The retreatment ratio was 7.6%. The exposure time of the corneal epithelium to alcohol (20% ethanol) was 30 seconds plus an additional 10 to 15 seconds in cases of strong epithelial adherence. Laser ablation was performed with a Keracor 117 excimer laser (Chiron Technolas). The follow-up after the second LASEK treatment was 6 months.

RESULTS

The epithelial flap for repeated LASEK was successfully created in all 10 eyes. The postoperative course in the eyes was uneventful. Six months after LASEK enhancement, the SE refraction was within +/-0.5 D in all eyes. No eye lost more than 1 line of best corrected visual acuity, and the uncorrected visual acuity was 20/20 or better in 8 eyes. Significant haze was not observed after repeated LASEK (mean 0.35 before and 6 months after LASEK enhancement).

CONCLUSIONS

Laser-assisted subepithelial keratectomy enhancement appears to be safe and effective for the correction of residual myopia after primary LASEK. Repeated epithelial flap preparation is possible without technical modifications.

Histological and immunohistochemical findings after laser in situ keratomileusis in human corneas

PURPOSE

To describe histopathological and immunohistochemical findings in human corneas after myopic laser in situ keratomileusis (LASIK) followed by iatrogenic keratectasia and after hyperopic LASIK.

SETTING

Department of Ophthalmology, University of Innsbruck, Innsbruck, Austria.

METHODS

Clinical, histological, and immunohistochemical investigations were performed of 1 human cornea with iatrogenic keratectasia following myopic LASIK and 1 human cornea with irregular astigmatism and central scar formation after hyperopic LASIK. Corneal buttons were obtained during penetrating keratoplasty in both patients.

RESULTS

Histopathological examination showed thinning of the central stroma with a posterior residual thickness of 190 microm in the patient with iatrogenic keratectasia after myopic LASIK and significant midperipheral thinning in the patient who had hyperopic LASIK. However, this characteristic ablation profile of the stroma after hyperopic LASIK was partially mitigated and compensated by the epithelium, which was significantly thinned in the center and markedly thickened in the midperiphery. Traces of wound healing with minimal scar tissue were present at the flap margin after myopic and hyperopic LASIK. In a few sections of the cornea with keratectasia after myopia LASIK, only a few collagen lamellae were visible crossing between the posterior residual stroma and the superficial flap. Immunohistochemical examination revealed minimally increased staining of dermatan sulfate proteoglycan within the stroma adjacent to the interface of the microkeratome incision. Increased staining of hepatocyte growth factor was found on keratocytes/fibroblasts at the flap margin in both corneas.

CONCLUSIONS

The wound-healing response is generally poor after LASIK, which may result in significant weakening of the tensile strength of the cornea after myopic LASIK, probably due to biomechanically ineffective superficial lamella. After LASIK in patients with high hyperopia, compensatory epithelial thickening in the annular midperipheral ablation zone might be partly responsible for regression.

Vitality of epithelial cells after alcohol exposure during laser-assisted subepithelial keratectomy flap preparation

PURPOSE

To evaluate the vitality of epithelial cells after various exposure times to 20% ethanol and epithelial flap preparation in laser-assisted subepithelial keratectomy (LASEK) using the trypan blue dye test.

SETTING

University Eye Clinic Regensburg, Regensburg, Germany, and the Rayne Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.

METHODS

Five human cadaver eyes were exposed to 20% ethanol for 15, 30, 45, 60, and 120 seconds, respectively. After an epithelial flap (as in LASEK) was prepared, the flap was deliberately cut off. The flaps were soaked in a trypan blue 0.1% solution at 37 degrees C. After 3 washes with phosphate-buffered saline (PBS), the specimens were reincubated for 30 minutes in culture medium containing 10% fetal calf serum at 37 degrees C. After an additional wash with PBS, the cells were observed with a standard inverted light microscope.

RESULTS

After 15- and 30-second exposure to 20% ethanol, most epithelial cells were vital. This changed substantially after 45 seconds, when vital and dead cells were approximately equal. Longer exposure times (60 seconds and 120 seconds) showed predominantly dead epithelial cells.

CONCLUSIONS

Exposure to 20% ethanol should be 20 to 30 seconds as the number of vital epithelial cells rapidly decreased after that. Vitality of the epithelial flap is probably a crucial factor in the dampened wound response in LASEK compared to that in photorefractive keratectomy.

Corneal haze after photorefractive keratectomy for myopia: role of collagen IV mRNA typing as a predictor of haze

PURPOSE

To develop a test based on the individual expression of collagen type IV synthesis in corneal epithelial cells to identify patients who have the potential for significant corneal haze after myopic photorefractive keratectomy (PRK).

SETTING

Department of Ophthalmology and the Institute of Microbiology, University of Regensburg, Germany.

METHODS

The individual synthesis of collagen type IV alpha3 mRNA was quantitatively measured in corneal epithelial cells of 34 eye (34 patients) with myopia ranging from -1.5 to -10.0 diopters (D) by a polymerase chain reaction (PCR) test. The corneal epithelial cells were collected before the PRK procedure. Collagen type IV alpha3 mRNA levels were correlated to postoperative haze and regression at 12 months.

RESULTS

In all samples, collagen type IV alpha3 mRNA was detected; the mean was 1.47 (range 0.11 to 6.42). There was a correlation between haze and the amount of collagen type IV alpha3 mRNA; that is, eyes with haze had more collagen IV expression. In contrast, no correlation was observed between regression and the amount of collagen type IV alpha3 mRNA.

CONCLUSIONS

The results show that collagen type IV alpha3 is an important factor in the development of corneal haze after PRK. Based on a quantitative PCR test, the individual collagen IV mRNA concentration in corneal epithelial cells could be measured. Further development could establish a screening test by which eyes with pronounced synthesis of collagen IV could be identified as being at high risk for haze after PRK.

Thermal consequences of photorefractive keratectomy

PURPOSE

Photorefractive keratectomy (PRK) is still a widely used method for the correction of refractive error despite the advent of laser in situ keratomileusis (LASIK). However, both procedures are associated with significant side effects such as corneal haze and regression. Several factors have been implicated in the etiology of haze, one of which is thermal loading of the cornea. The purpose of this study was to investigate the temperature changes occurring during PRK when performed at different ablation depths.

METHODS

Noncontact, color-coded ocular thermography was performed with an infrared detector apparatus during PRK ablation on 19 ovine corneas. Five different refractive corrections were carried out ranging from -2.00 diopters (D) (ablation depth, 31.2 microm) to -10.00 D (ablation depth, 137.9 microm).

RESULTS

A temperature rise at the corneal surface was demonstrated in all 19 corneas. The mean rise in temperature was 7.35 +/- 1.13 degrees C with a maximum rise in temperature of 8.97 degrees C. A positive correlation was found between the refractive correction and the peak rise in temperature (r2 = 0.57, p< 0.0001). The rate of temperature change was greater for smaller treatments than for larger treatments (r2 = 0.79, p < 0.0001). Corneas undergoing larger treatments were subject to greater rises in temperature for longer periods of time.

CONCLUSIONS

This study suggests that the cornea undergoes a significant rise in temperature as a result of the PRK process. Further investigation is required to determine what effect this thermal loading has on the corneal wound healing response after PRK.

Immunohistochemical Study of Subepithelial Haze After Phototherapeutic Keratectomy

PURPOSE

Subepithelial haze is a frequent complication and is often the cause of regression after photorefractive keratectomy (PRK). The lack of understanding of this undesirable complication following PRK is in part due to the limited availability of suitable tissues for pathological studies.

METHODS

We examined the expression of various extracellular components in the cornea of a 46-year-old man who underwent phototherapeutic keratectomy (PTK) to remove a central corneal scar secondary to trauma. The patient subsequently underwent penetrating keratoplasty. A scar-free region containing an area of slight subepithelial haze adjacent to normal cornea was used for immunohistochemical staining with antibodies directed against cytoskeletal proteins, ie, vimentin, desmin and smooth muscle actin, and the extracellular components, laminin, heparan sulfate, keratan sulfate, and collagen types III, IV, V, and VII.

RESULTS

Immunohistochemistry revealed that basal epithelial cells expressed components of basement membrane. The stromal fibroblasts within the haze tissue were labeled by anti-smooth muscle actin antibodies, a characteristic of myofibroblasts, which synthesized and secreted extracellular matrix components that contributed to the formation of the disorganized collagenous matrix and may account for subepithelial haze.

CONCLUSIONS

The expression patterns for the cytoskeletal proteins and extracellular components indicated that the formation of subepithelial haze is a process of tissue remodeling, involving both corneal basal epithelial cells and keratocytes during wound repair.

Regression and epithelial hyperplasia after myopic photorefractive keratectomy in a human cornea

We present the histology of a cornea of a woman who had excimer laser photorefractive keratectomy (PRK) for myopia 6 months before she died in an accident. Preoperative spherical refraction was -6.00 diopters (D) with an astigmatism of -0.50 D. Six months postoperatively, refraction was -4.50 D. Slight corneal haze was noted at 1 and 3 months. The corneal histology showed marked epithelial hyperplasia in the center of the ablation zone without subepithelial deposition of newly synthesized collagen, proteoglycans, or both. The epithelial thickness was 38 microns in the untreated area and 93 microns in the center of the ablation. In conclusion, postoperative epithelial hyperplasia was responsible for regression after PRK in this eye.

Differences in Keratocyte Apoptosis Following Transepithelial and Laser-scrape Photorefractive Keratectomy in Rabbits

BACKGROUND

Anterior stromal keratocyte cells undergo programmed cell death (apoptosis) in response to corneal epithelial injury. Keratocyte apoptosis may be an initiator of the corneal wound healing response that includes keratocyte proliferation and activation, as well as changes to the overlying epithelium, occurring following refractive surgical procedures such as photorefractive keratectomy (PRK). This study compared the effect of laser-scrape and transepithelial PRK on keratocyte apoptosis.

METHODS

Photorefractive keratectomy was performed in both eyes of 10 New Zealand white rabbits using the Summit Apex excimer laser. Surgery was performed using transepithelial PRK in one eye and laser-scrape PRK in the other. The central cornea was analyzed at 4 hours after surgery using a quantitative TUNEL assay that detects fragmented DNA characteristic of apoptosis. Hepatocyte growth factor (HGF) production by keratocytes was detected by immunocytochemistry.

RESULTS

Average apoptotic cells per 400X microscopic field determined by 2 independent masked observers were 0.9 +/- 0.5 (scanning electron microscopy) and 0.2 +/- 0.2 in the transepithelial PRK group compared with 5.1 +/- 2.9 and 4.1 +/- 3.2 in the laser-scrape group. The difference between the two groups was statistically significant for both observers (P < .05, ANOVA). HGF was detected within keratocytes throughout the corneal stroma. Less HGF was detected in the anterior stroma in the laser-scrape group at 4 hours after surgery, consistent with more anterior keratocyte apoptosis in this group.

CONCLUSIONS

Transepithelial PRK induced less anterior keratocyte apoptosis in rabbits than laser-scrape PRK. This suggests that transepithelial PRK could be useful in preventing or minimizing refractive regression and subepithelial scarring.