Long-term corneal keratocyte deficits after PRK and LASIK: in vivo evidence of stress-induced premature cellular senescence

Change in keratometry after myopic laser in situ keratomileusis and photorefractive keratectomy

PURPOSE

To compare the change in keratometry (K), spherical equivalent (SE), and visual acuity after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).

SETTING

Academic tertiary care center.

DESIGN

Retrospective review.

METHODS

The postoperative K, SE, and uncorrected and corrected distance visual acuities were measured 6 months, 9 months, 1 year, 2 years, 3 years, 4 to 5 years, 6 to 7 years, and 8+ years postoperatively. A difference (Δ) for each variable was calculated from its 6-month postoperative baseline. The rates of change were grouped based on the magnitude of myopic correction (0.00 to 2.99 diopters [D]; 3.00 to 5.99 D; 6.00 to 8.99 D), type of surgery (LASIK versus PRK), and age (<34 years; 34 to 45 years; >45 years).

RESULTS

Statistically significant differences were found in the rates of change between low and moderate corrections to high corrections for ΔKavg (P=.0472 and P=.0091, respectively) and ΔSE (both P<.0001). Statistically significant differences were found in the rate of change in ΔKavg between all 3 ages groups (P=.0330, P=.0051, and P<.0001) and in ΔSE between ages less than 34 years and 34 to 45 years to ages over 45 years (P=.0158 and P=.0015, respectively). There was no significant difference in the rate of change in ΔKavg and ΔSE between LASIK and PRK (P=.3599 and P=.9403, respectively).

CONCLUSION

There was keratometric and refractive regression for myopic LASIK, with the rate of regression depending on treatment magnitude and age.

FINANCIAL DISCLOSURE

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

Confocal microscopy of corneal stroma and endothelium after LASIK and PRK

PURPOSE

To compare with confocal microscopy the changes in stromal keratocyte density and endothelial cell count due to photorefractive keratectomy (PRK) and LASIK.

METHODS

In this prospective study, 32 eyes (16 myopic patients) were examined with the NIDEK Confoscan 3 confocal microscope before and 6 months after PRK and LASIK. The preoperative mean myopia was -2.85+/-0.99 diopters (D) (range: -1.00 to -4.00 D) in 24 eyes that underwent PRK and -2.94+/-0.96 D (range: -2.00 to -4.25 D) in 8 eyes that underwent LASIK. Keratocyte density in the anterior and posterior stroma and the endothelial cell count were measured. Statistically significant changes were assessed using the t test. P<.05 was considered statistically significant.

RESULTS

Preoperative hexagonal cell percentage in the LASIK group was 52.17+/-11.43 and 51.33+/-10.98 in the PRK group. Postoperatively, the percentages were 52.96+/-7.55 and 53.34+/-10.2, respectively. Six months postoperatively, keratocyte density changed by 367.12+/-103.35 cells/mm(2) (34.7% reduction) in the anterior stroma (P<.05) and 9.25+/-28.28 cells/mm(2) (1.31% reduction) in the posterior stroma (P>.05) for the LASIK group. In the PRK group, these values were 319.71+/-83.45 cells/mm(2) (31.13% reduction) in the anterior stroma (P<.05) and 0.17+/-38.97 cells/mm(2) (0.02% reduction) in the posterior stroma (P>.05). The changes in keratocyte densities were not statistically significant between groups (P>.05). The mean number of keratocytes decreased by 37.2% in the retroablation zone of the LASIK group (P<.05). No changes were noted in endothelial cell counts.

CONCLUSIONS

A significant decrease occurred in the number of stromal keratocytes in the anterior stroma. Despite differences in surgery, the change in keratocyte density and endothelial cell counts were similar between LASIK and PRK groups (P>.05).

A transcriptomic analysis of the EK1.Br strain of human fibroblastoid keratocytes: the effects of growth, quiescence and senescence

There is a growing need within ocular research for well-defined cellular models of normal corneal biology. To meet this need we created and partially characterised a standard strain of human fibroblastoid keratocytes (EK1.Br) and demonstrated that phenotypic changes occur within these cells with replicative senescence in vitro. Using Affymetrix HG-U133A oligonucleotide arrays, this paper reports both a comprehensive analysis of the transcriptome of EK1.Br in the growing, quiescent and senescent states and a comparison of that transcriptome with those of primary corneal endothelium, lung fibroblasts and dermal fibroblasts grown under identical conditions. Data mining shows (i) that EK1.Br retain the characteristic transcriptional fingerprint of keratocytes in vitro (ii) that this phenotype can be distinguished from those of other 'fibroblasts' by groups of highly differentially expressed genes and (iii) that senescence induces a distinct dedifferentiation phenomenon in EK1.Br. These findings are contextualised into the broader literature on replicative senescence and are supported with a web-accessible and fully searchable public-access database (www.madras.cf.ac.uk/cornea).