Excimer laser effects on human corneal endothelium. Modulation by serum factor(s)

Recombinant human serum albumin for corneal preservation

PURPOSE

To study the performance of a completely synthetic organ culture (OC) preservation system containing recombinant human serum albumin (rHSA) for preservation of human donor corneas.

METHODS

Twenty-four paired donor corneas were randomly collected, and one cornea from each donor was preserved in synthetic (experimental) and serum-based media (control). The tissues were assessed at day 0; after 6 days of preservation at room temperature (RT) in Cornea Trans^® and Cornea Prep II^® ; after 28 days at 31°C in Cornea Syn^® [with rHSA] and Cornea Max^® [with foetal calf serum (FCS)] and; 4-day post deswelling in Cornea Trans^® and Cornea Jet^® . Thickness was determined with optical coherence tomography (OCT) and transparency with a validated, custom device. Morphology, endothelial cell density (ECD) and mortality were observed after treating the tissues with Trypan blue and sucrose. Glucose uptake by the cells was analysed. Data were compared using non-parametric paired Wilcoxon tests with p < 0.05 deemed significant. Histology using periodic acid-schiff (PAS), expressions of p63, CK12, αSMA and ZO-1 were analysed, and cell apoptosis postpreservation was studied.

RESULTS

Corneas stored in synthetic media showed a higher and statistically significant value as compared to serum-based media in terms of viable endothelial cell density (VECD), mortality, morphology and glucose uptake postpreservation. Histology showed presence of all the layers, all the markers were expressed, and no apoptosis was observed in either media.

CONCLUSION

The new synthetic preservation system containing rHSA (and other confidential constituents) showed better preservation effects than traditional media containing serum.

Synthetic versus Serum-Based Medium for Corneal Preservation in Organ Culture: A Comparative Study between 2 Different Media

Purpose

To study the effect of a synthetic medium and compare it with a serum-based medium for corneal preservation in organ culture using an overall quality assessment system.

Methods

A randomized study with blinded observers was performed comparing parameters such as thickness, transparency, viable endothelial cell density (VECD), morphology, and overall quality (OQ) of the corneal tissues preserved in synthetic and a serum-based medium, respectively. Seven human paired corneas were randomly selected and assessed at day 0 (initial), day 2 (before organ culture), day 30 (before deturgescence/ deswelling storage), and 48 hours post deswelling. Thickness was determined with optical coherence tomography and transparency with a validated, custom device. The morphology and VECD were observed after treating the tissues with trypan blue and sucrose. Data were compared using paired t tests with p<0.05 deemed significant.

Results

Parameters were similar at the initial stage between the groups with no statistically significant difference. However, after preservation in the deturgescent medium, the corneas stored in a serum-based medium showed a higher and statistically significant OQ value (p = 0.0317).

Conclusions

The OQ of a serum-based medium was higher than that of the synthetic medium. A higher rate of transparency and reduction in thickness was observed in the serum-based medium at the end of the storage. Although complete synthetic media may have distinct advantages of being serum/animal-free, the quality of the cornea is of a reasonable concern when it is deemed for transplantation.

Effect of Laser in situ Keratomileusis on the Corneal Endothelium

PURPOSE

To assess the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium.

METHODS

In a prospective study, preoperative and 12-month postoperative specular microscopy of the central corneal endothelium and corneal thickness assessment was done in 180 eyes of 105 patients (mean age 31.96 +/- 8.88 years; range 16 to 55 yr) who had LASIK to correct myopia. The central endothelium was analyzed for several parameters including cell density, coefficient of variation, and corneal thickness. Preoperative and postoperative data were compared.

RESULTS

The mean preoperative endothelial cell density was 2,547.37 +/- 282.00 cells/mm2, mean coefficient of variation of cell size was 58.33 +/- 11.50%, and mean central corneal thickness was 558.90 +/- 28.42 microm. There was not a statistically significant change in mean endothelial cell density (2,508.24 +/- 289.57 cells/mm2) or mean coefficient of variation (58.61 +/- 9.89%) at 1 year after surgery (P >.05 ). Average endothelial cell loss was 1.54% at 1 year after surgery. Mean central corneal thickness at 12 months postoperatively was 493.24 +/- 52.55 microm (P<.01).

CONCLUSION

LASIK did not appear to alter corneal endothelial cell density at 12 months postoperatively.

Simple organ cornea culture model for re-epithelialization after in vitro excimer laser ablation

BACKGROUND AND OBJECTIVE

Most of the in vitro work to characterize the effects of clinical laser surgery on corneal tissues has concentrated on the effects on stromal keratocytes and endothelium with little attention being paid to corneal epithelium. Our purpose is to describe the epithelial healing rates observed in freshly cultured rabbit corneas treated with phototherapeutic keratectomy (PTK).

STUDY DESIGN/MATERIALS AND METHODS

Corneas were placed in a simple organ culture system, with media change every 2 days. A clinical excimer laser was used to perform a 6 mm diameter, 100 microm depth transepithelial PTK on 24 cultured rabbit corneas, 1 day after culture initiation. For each post-treatment day, one experimental and one control cornea were removed from culture and stained with fluorescein, photographed, and fixed for histology. Epithelial defect area was measured with digital imaging software and analyzed statistically to assess the re-epithelialization rate.

RESULTS

Control corneas, maintained in culture for 1-4 days, had no epithelial defects. Those corneas treated with PTK exhibited an immediate epithelial defect that slowly healed over 3 days. This was confirmed on histopathological analysis. A significant linear trend in re-epithelialization across the time points studied was found (F = 80.48, P = 0.0029). The slope of the linear regression model showed an estimate rate of re-epithelialization of -6.70 over the 3 days.

CONCLUSION

We have described the development of a simple, whole organ, rabbit cornea culture model for re-epithelialization after PTK. Our rates of epithelial healing resemble those found in the literature in live rabbit models. Therefore, this model may possibly be used to monitor epithelial wound healing in different corneal diseases or injuries.

Acute corneal endothelial changes after laser in situ keratomileusis

PURPOSE

To report the acute effects of laser in situ keratomileusis (LASIK) on the corneal endothelium.

METHODS

Twenty eyes of 10 consecutive patients (mean age, 38.1 +/- 10.84 years) underwent bilateral simultaneous LASIK for myopic astigmatism (spherical equivalent ranging from -1.75 to -7.13 diopters) without any complications. Each eye was evaluated by slit-lamp biomicroscopy and noncontact specular microscopy preoperatively, within 15 minutes after LASIK and 1 day after surgery. Specular microscopy images were then analyzed to calculate endothelial cell density (ECD), coefficient of variation (CV) of cell size, and percentage of hexagonal cells.

RESULTS

All corneas demonstrated marked alterations in endothelial cell morphology by slit-lamp biomicroscopy within 15 minutes after surgery that resolved by the first postoperative day. Central corneal endothelial analysis by noncontact specular microscopy confirmed pleomorphism with definite loss of hexagonality. Mean ECD was calculated to be 2,816.3 +/- 286.02 cells/mm(2) preoperatively, 2,750.85 +/- 327.95 cells/mm(2) on day 0 (p = 0.395), and 2,810.55 +/- 218.48 cells/mm(2) on day 1 (p = 0.461). Mean CV was 32.65 +/- 7.29 preoperatively, 34.4 +/- 6.19 on day 0 (p = 0.412), and 30.9 +/- 5.54 on day 1 (p = 0.067). Mean percentage of hexagonal cells was 63.35 +/- 10.76 preoperatively, 47.55 +/- 9.69 on day 0 (p = 0.000009), and 60 +/- 9.3 on day 1 (p = 0.00003).

CONCLUSION

Qualitative and quantitative changes in endothelial cell morphology (i.e., decreased endothelial cell hexagonality) demonstrate that LASIK does induce an acute effect on the corneal endothelium that may represent transient endothelial cell edema.

Stress wave amplitudes during laser surgery of the cornea

PURPOSE

To determine the stress wave amplitudes generated during photoablation of the cornea using an argon fluoride excimer laser.

DESIGN

Experimental study using porcine eyes.

METHODS

Profiles of the stress wave amplitudes and enucleated human eyes along the axis of symmetry of porcine eyes and enucleated human eyes were measured using a miniature piezoelectric transducer. The ablation parameters, fluence, and ablation diameters were varied within the range of clinical application.

MAIN OUTCOME MEASURES

Stress wave amplitudes generated during photoablation.

RESULTS

The stress waves pass through a pressure focus located in the posterior lens and anterior vitreous, where amplitudes of up to 100 atm were measured with a 6-mm or larger ablation zone. Posterior to this focus, the stress wave amplitudes rapidly decrease to less than 10 atm at the retinal site. Small diameter excimer laser spots (< or =1.5 mm) produce a declining stress wave with no pressure focus at the lens and anterior vitreous.

CONCLUSIONS

Stress waves may be potentially hazardous to anterior structures of the human eye, including the corneal endothelium, lens and anterior vitreous face. They peak at the lens and vitreous with a broad beam, but not with small spot laser ablation. At posterior retinal and subretinal structures, they may be considered harmless.

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively

PURPOSE

To investigate the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively.

METHODS

Patients who were subjects of a previous prospective study (Am J Ophthalmol 125:465-471, (April) 1998) were contacted for a follow-up analysis of the central corneal endothelium. Noncontact specular microscopy was performed 35 to 37 months after LASIK on 52 eyes of 27 patients of the original cohort of 98 eyes of 65 patients and six eyes of three patients who were previously lost to follow-up after their initial post-LASIK evaluation. Patient age ranged from 29 to 66 years at the time of the original LASIK procedure. Attempted corrections ranged from 2.25 to 14.5 diopters of myopia, giving theoretical ablation depths of 182 to 332 microm below the corneal surface. Forty-eight eyes (83%) had a history of preoperative contact lens use (3 to 33 years). Central endothelial cell density, coefficient of variation of cell size, and percent of hexagonal cells were analyzed using 72 to 152 cells from each image. Multivariate analysis was used to search for factors that might predict changes in cell density, coefficient of variation, and percent of hexagonal cells.

RESULTS

The mean +/- SD preoperative cell density was 2,498 +/- 354 cells per mm(2), the mean coefficient of variation was 0.36 +/- 0.07, and the percent of hexagonal cells was 58 +/- 6. Three years after surgery there was no statistically significant change in the mean endothelial cell density (2,489 +/- 335 cells per mm(2); P = 0.88, paired t test) or the percent of hexagonal cells (60 +/- 7; P = 0.14, paired t test). The mean coefficient of variation was significantly lower postoperatively (0.32 +/- 0.04; P = 0.0006, paired t test); a repeated measures analysis showed that this significant improvement could not be explained by cessation of contact lens wear after LASIK (P = 0.34). Multivariate analysis did not identify any factors that were predictive of change in cell density, coefficient of variation, and percent of hexagonal cells.

CONCLUSIONS

Laser in situ keratomileusis for the correction of 2.25 to 14.5 diopters of myopia had no significant effect on central corneal endothelial cell density or the percent of hexagonal cells 3 years after surgery. The coefficient of variation of cell size improved significantly 3 years after surgery.

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium

PURPOSE

To assess the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium.

METHODS

In a prospective study, the corneal endothelium of 98 eyes of 65 consecutive patients (mean age, 41 years; range, 22 to 66 years) was photographed before, 2 weeks after, and 12 weeks after LASIK for the correction of 2.75 to 14.5 diopters of myopia. Theoretical ablation depths were 200 to 330 microm below the corneal surface. Cell density, coefficient of variation, and percent of hexagonal cells were determined using 150 to 200 cells from each image. Eighty-eight eyes (91%) of 59 patients had a history of contact lens wear.

RESULTS

The mean+/-SD preoperative endothelial cell density was 2,549+/-365 cells per mm2, and the mean coefficient of variation was 0.35+/-0.06. There was no statistically significant change in the mean endothelial cell density or mean coefficient of variation of cell size at the 2-week (2,561+/-360 cells per mm2 and 0.35+/-0.06) or 12-week (2,541+/-364 cells per mm2 and 0.35+/-0.05) postoperative examinations. The percent of hexagonal cells was not significantly changed 2 weeks postoperatively; however, 12 weeks postoperatively (P=.0413, two-tailed t test), the percent of hexagonal cells was decreased by 1%.

CONCLUSIONS

Corneal endothelial cell density and morphology were unchanged 2 and 12 weeks after LASIK for the correction of up to 14.5 diopters of myopia. In this LASIK study, the correction of up to 14.5 diopters of myopia appears to cause no clinically significant effect on corneal endothelial cell density or morphology.