Specular microscopy of the corneal endothelium after excimer laser photorefractive keratectomy

Long term results of no-alcohol laser epithelial keratomileusis and photorefractive keratectomy for myopia

AIM

To evaluate the long term clinical results of mechanical no-alcohol-assisted laser epithelial keratomileusis (LASEK) versus standard photorefractive keratectomy (PRK) for low-moderate myopia.

METHODS

Twenty-five eyes treated with LASEK and twenty-five eyes treated with PRK were evaluated with a mean follow-up duration of 60mo. Mechanical separation of the epithelium was performed with blunt spatula and without application of alcohol. Laser ablation was performed with the MEL-70 excimer laser. All patients were examined daily until epithelial closure; at 1, 3, 6, and 12mo, and every year subsequently. Main outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, haze, efficacy and safety indexes.

RESULTS

Twenty-one eyes and 22 eyes completed follow-up of 60mo in LASEK and PRK group respectively. Manifest refraction at 60mo follow-up was -0.01 and 0.26 in LASEK and PRK group respectively. In the LASEK group mean UDVA and mean CDVA after 60mo were 20/22 and 20/20 respectively (P>0.01). In the PRK group mean UDVA and mean CDVA at 60mo follow-up were 20/20 and 20/20 after 60mo (P>0.01). The efficacy indexes were 0.87 and 0.95, and the safety indexes were 1.25 and 1.4 respectively for LASEK group and PRK group.

CONCLUSION

Both standard PRK and no-alcohol LASEK offer safe and effective correction of low-moderate myopia in the long term without any statistically significant difference between the two groups.

Photorefractive keratectomy in posterior polymorphous dystrophy with vesicular and band subtypes

PURPOSE

To evaluate the safety and efficacy of photorefractive keratectomy (PRK) in patients with posterior polymorphous dystrophy (PPMD) with vesicular and band subtypes.

SETTING

Walter Reed Center for Refractive Surgery, Washington, DC, USA.

DESIGN

Case series.

METHODS

The records of patients with PPMD who had PRK between January 2002 and May 2009 were reviewed. Data for analysis included sex, age, ablation depth, residual stromal bed thickness, manifest spherical equivalent, uncorrected (UDVA) and corrected (CDVA) distance visual acuities, central corneal thickness (CCT), endothelial cell density (ECD), intraocular pressure (IOP), and complications. Preoperative and postoperative results were compared using the Wilcoxon signed-rank test, with P < .05 considered significant.

RESULTS

Fourteen eyes of 7 men (mean age 29.1 years ± 9.1 [SD]; range 21 to 42 years) with at least a 6-month follow-up were reviewed. At the final follow-up (mean 19.5 months; range 6.3 to 58.3 months), all eyes had a UDVA of 20/15 and all eyes were within ± 0.50 diopter of emmetropia. The CDVA was unchanged from preoperatively in 71.4% of eyes and improved by 1 line in 28.6%. There were no significant complications. The IOP did not change significantly over the follow-up (P = .272). At the final visit, the mean ECD (2795.3 ± 366.0 cells/mm(2)) was unchanged from baseline (2809.1 ± 338.3 cells/mm(2)) (P = .114).

CONCLUSIONS

Photorefractive keratectomy in PPMD patients with vesicular and band subtypes resulted in excellent visual outcomes and a low incidence of adverse effects. Endothelial cell densities did not change significantly in the early postoperative period.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Short-term corneal endothelial changes after laser-assisted subepithelial keratectomy

To investigate the short-term effects of laser-assisted subepithelial keratectomy (LASEK) on the corneal endothelium, 10 patients undergoing LASEK for myopia without complications (20 eyes) were observed. Each eye was evaluated by slit-lamp biomicroscopy and non-contact specular microscopy pre-operatively, and at 15 min, 1 day and 1 week post-operatively. The decrease in endothelial cell density was statistically significant at 15 min post-operatively, and the difference between pre-operative and 15-min post-operative coefficient of variation of cell size was also statistically significant. The percentage of hexagonal cells was significantly different from baseline levels at 15 min and at 1 day post-operatively. All parameters at 1 week post-operatively were not statistically different from those observed pre-operatively. Immediate changes in endothelial cell number and morphology occurred following LASEK, but endothelial morphology returned to the pre-operative condition after 1 week. Long-term follow-up is needed to identify further consequences of this procedure.

Corneal endothelial cell density after femtosecond thin-flap LASIK and PRK for myopia: a contralateral eye study

PURPOSE

To compare the effect of femtosecond thinflap LASIK and photorefractive keratectomy (PRK) on postoperative endothelial cell density.

METHODS

In a prospective, randomized, contralateral, single-center clinical trial, 25 patients (mean age: 30+/-5 years [range: 21 to 38 years]) underwent PRK in one eye and thin-flap LASIK in the fellow eye for the correction of myopia using a wavefront-guided platform. The central corneal endothelial cell density was measured using the NIDEK Confoscan 4 preoperatively, and at 1 and 3 months postoperatively. Changes in endothelial cell density were analyzed over time between the two refractive techniques.

RESULTS

In PRK, the average preoperative endothelial cell density was 3011+/-329 cells/mm(2), which decreased to 2951+/-327 cells/mm(2) at 1 month (P=.5736) and 2982+/-365 cells/mm(2) at 3 months (P=.6513). In thinflap LASIK, the average preoperative endothelial cell density was 2995+/-325 cells/mm(2), which decreased to 2977+/-358 cells/mm(2) at 1 month (P=.5756) and 2931+/-369 cells/mm(2) at 3 months (P=.4106). No statistically significant difference was found between the two groups at 1 (P=.7404) or 3 (P=.3208) months postoperatively.

CONCLUSIONS

No statistically significant change was noted in endothelial cell density following either PRK or thin-flap LASIK for the treatment of myopia. Furthermore, no statistically significant difference was found between the two groups out to 3 months postoperatively, indicating that thin-flap LASIK is as safe as PRK with regards to endothelial health.

Laser in situ keratomileusis in patients with posterior polymorphous dystrophy

PURPOSE

To report short-term results of LASIK in 4 eyes with the vesicular form of posterior polymorphous dystrophy (PPMD).

METHOD

A review was performed of 2 patients with PPMD who underwent bilateral LASIK. Patients were asymptomatic at the time of presentation and had no prior ocular history. Preoperative measurements were made of uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal pachymetry, and endothelial cell density (ECD). All 4 eyes underwent uneventful LASIK. Postoperative measurements of UCVA and BSCVA were performed at follow-up visits 1 day, 1 month, 3 months, and 1 year after surgery, along with pachymetry and ECD measurements at the 3-month and 1-year visits. Results were analyzed.

RESULTS

At 1 year, all eyes had an UCVA equal to or better than 20/25 and BSCVA equal to or better than 20/20. There was a small mean endothelial cell loss (2.3%) at 1 year. No adverse events were experienced.

CONCLUSIONS

Short-term results indicate efficacy and safety of LASIK on eyes with posterior polymorphous dystrophy. Further study is needed to assess long-term outcomes in a larger study population.

Corneal decompensation after laser in situ keratomileusis in fuchs' endothelial dystrophy

PURPOSE

To report corneal decompensation after laser in situ keratomileusis (LASIK) in a patient with Fuchs' endothelial dystrophy.

METHODS

Observational case report.

RESULTS

A 47-year-old woman with cornea guttata without symptoms or findings of corneal edema had uneventful LASIK for -5.50 -0.50 x 150 in the right eye and -4.00 -1.25 x 170 in the left eye. Postoperatively, she developed corneal edema, with significant loss of best-corrected visual acuity in both eyes. Preoperative corneal thickness was 587 microm in the right eye and 549 microm in the left eye, measured by ultrasound pachymetry. These readings were 550 and 560 microm on day 67 postoperatively. Endothelial cell counts showed means of 1209 and 1661 cells/mm2 in the right and left eyes, respectively.

CONCLUSION

Caution is suggested when considering LASIK in eyes with severe cornea guttata.

Endothelial Cell Studies in Patients After Photorefractive Keratectomy for Hyperopia

PURPOSE

To report central and peripheral corneal endothelial cell studies performed as part of the VISX hyperopic photorefractive keratectomy (PRK) clinical trial.

METHODS

During this prospective, multicenter clinical trial, which was part of an FDA investigation, endothelial cell specular microscopy was done at five centers. Non-contact central and peripheral cell density, percent hexagonality, and coefficient of variability of cell size were obtained using the Konan Noncon Robo SP-8000FA with BAMBI analysis software. Data were gathered at baseline and at 1, 6, and 12 months after hyperopic PRK.

RESULTS

Analysis of results of 171 eyes demonstrated no statistically significant detrimental changes in the corneal endothelium at any postoperative time point. The statistically significant changes noted were interpreted as an improvement in cell morphology and were attributed to the cessation of contact lens wear following treatment.

CONCLUSION

Hyperopic PRK with the VISX STAR S2 Excimer Laser System produced no statistically significant adverse effect on the corneal endothelium.

Endothelial decompensation after laser in situ keratomileusis

We report the results of laser in situ keratomileusis (LASIK) in a 58-year-old woman with a history of corneal guttata in the right eye and mild Fuchs' dystrophy in the left eye. Preoperative pachymetry was 586 microm and 656 microm, respectively. The surgical treatment was +1.50 diopters (D) in the right eye and +3.25 D in the left eye. Surgery was performed using a VISX S2 Star laser and a Hansatome microkeratome with a 9.5 mm ring. Postoperatively, edema in the right eye resolved and pachymetry returned to 585 microm, but the left cornea decompensated despite maximum medical therapy and had a final pachymetry of 779 microm. The patient was referred to our cornea service for penetrating keratoplasty, which was performed 14 months after the LASIK treatment.

Iatrogenic Keratectasia Following Laser in situ Keratomileusis

PURPOSE

To evaluate keratectasia after laser in situ keratomileusis (LASIK) for high myopia.

METHODS

A 49-year-old male patient with myopia of -23.50 D in both eyes underwent LASIK with a Summit Technology Apex Plus excimer laser. A Moria manually-guided MDSC microkeratome was used. Preoperative corneal topography in both eyes did not reveal underlying or fruste form of keratoconus. Four months after LASIK, a progressive keratectasia occurred in right eye and after 12 months, in left eye. Corneal transplantation was performed in both eyes.

RESULTS

Histological and ultrastructural examinations were performed on one corneal button. The analysis showed regular stromal morphology and cellularity, with no sign of inflammation. The morphometric analysis showed an overall thickness of 334 microm, with a flap of 262 microm and a stromal residual bed of 72 microm, in the center of the button.

CONCLUSION

A LASIK corneal flap made with a planned 120-microm plate turned out histologically to be approximately 260 microm thick, in an eye with a refractive correction of -23.50 D. The excessive flap thickness and excessive ablation produced progressive keratectasia requiring a penetrating keratoplasty.

Growth factors in corneal wound healing following refractive surgery: A review

The first part of this review article aims to provide important basic definitions of growth factor terminology, and to put forward a model for understanding the role of growth factors in a wound healing context. In the second part of the paper, we review the literature on growth factors in the cornea, including that on changes associated with wound healing following refractive surgery in the epithelial, stromal, and endothelial layers. The role of growth factors in stromal removal, corneal neovascularization, corneal innervation and wound healing is considered. The importance of the epithelial-stromal interaction is discussed, including the role of growth factors in keratocyte apoptosis. In the final section, we review the current literature on endogenous and exogenous modulation of growth factors in corneal wound healing. This includes important in vitro work but aims to emphasize clinically relevant results. Photorefractive keratectomy (PRK) may have short-term complications such as pain and haze, whereas laser in situ keratomilieusis (LASIK) may have longer-term adverse effects on corneal biomechanics. The emerging technique of laser epithelial keratomilieusis (LASEK) provides an interesting alternative wound which may be less susceptible to the inherent complications of PRK and LASIK. At present, the phenomenon of iatrogenic keratectasia following LASIK is not fully understood, but these features of wound healing following PRK may be amenable to growth factor modulation.