We appreciate Dr Dille’s comments on our manuscript published in the American Journal of Ophthalmology in August 2014.

The corneal epithelium has a rapid cell turnover and is reactive to asymmetries in the shape of the underlying stromal surface. In keratoconic eyes, cross-sectional high-resolution spectral-domain optical coherence tomography (SD OCT) scans showed localized areas of epithelial compensation overlying areas of stromal thinning. Significant regional variability in corneal epithelial thickness profiles is observed in keratoconus and postoperative corneal ectasia, compared with normal eyes. These compensatory changes of the corneal epithelium help to generate a smoother corneal surface in the setting of irregularities of the underlying stroma. Whether the lack rigidity of a floppy eyelid contributes to the lack of rigidity of the keratoconic cornea cannot be directly inferred by the findings of epithelial smoothing and regional thickness variation in keratoconus. However, Dr Dille’s implied association cannot be dismissed by these findings either.

In our recent study, we described detailed analysis of the corneal epithelial and flap thickness remodeling in laser-assisted in situ keratomileusis (LASIK) using high-resolution SD OCT. The apparent early central thinning (1 week postoperative) of the corneal epithelium observed after myopic LASIK implies that either localized surface dryness or the aspheric laser ablation profile, which includes a spherical aberration compensation (aspheric ablation) that results in increased paracentral ablation compared to old lasers, plays a role in this early distribution profile of the corneal epithelium. Therefore, the corneal epithelium compensates for this transition zone being slightly thinner centrally as the epithelium further remodels with prolonged blinking of the eyelid. Progressive epithelial and flap thickening with mild changes in corneal power were then observed with consequent stabilization between 3 and 9 months postoperatively. The fact that the magnitude of epithelial thickening correlated to the preoperative myopic refractive error indicates that the cornea (together with the blinking eyelid) desires a smoother contour, which the epithelium nicely provides. In our study, we also observed thickening of the corneal epithelium inferiorly, which also has been reported in normal eyes. It is important to clarify that the epithelial thickness measurements using SD OCT also include the tear film. We believe that the eyelid position, tear film distribution, and gravity may play a role in the corneal epithelial thickness distribution. Furthermore, the wavefront optimized ablation profile is centered on the pupil and the SD OCT scans were centered at the corneal vertex, giving the appearance that the epithelium is thicker inferiorly. We believe the pattern of epithelial remodeling with different ablation profiles should be considered in the future planning of customized excimer laser ablations, including topography-guided, wavefront-guided, and multifocal, presbyopic excimer laser treatments.

We would like to thank Dr Dille for drawing attention to our findings in this light, and giving us further insight to consider in the future.

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Jan 7, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Reply

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