Corneal thickness changes in hyperopic orthokeratology measured by optical pachometry

Area of Science:

• Ophthalmology
• Corneal Physiology
• Refractive Error Correction

Background:

• Orthokeratology (OK) lenses reshape the cornea to correct refractive errors.
• Hyperopic OK aims to correct farsightedness, but its corneal mechanisms are less understood than myopic OK.
• Understanding corneal changes is crucial for optimizing OK lens design and patient outcomes.

Purpose of the Study:

• To investigate the time course of corneal thickness changes during a 4-day period of overnight hyperopic orthokeratology (OK) lens wear.
• To differentiate between central and para-central corneal responses to hyperopic OK.
• To correlate corneal structural changes with refractive and topographic outcomes.

Main Methods:

• Fourteen subjects wore hyperopic OK lenses in one eye overnight for 4 nights, with the fellow eye as a control.
• Measurements included subjective refraction, corneal topography, and corneal thickness using optical pachometry.
• Data were collected at lens removal (AM) and 8 hours post-removal (PM) on days 1 and 4.

Main Results:

• Significant refractive and topographic changes were observed throughout the study.
• Central corneal thickness increased at AM visits due to stromal edema, resolving by PM.
• Para-central corneal epithelium thinned consistently, counteracting stromal thickening and leading to overall para-central thinning by PM.

Conclusions:

• Para-central epithelial thinning is the primary mechanism for anterior corneal steepening in hyperopic OK.
• This epithelial change sufficiently explains the induced refractive response in hyperopic OK.
• Unlike myopic OK, corneal thickening is not a significant factor in hyperopic OK, potentially explaining its reduced efficacy.