Time course of corneal topographic changes in the first week of overnight hyperopic orthokeratology

To investigate the time course of refractive and corneal topographic changes in overnight hyperopic orthokeratology (OK).

Ten young adult subjects were fitted with rigid hyperopic OK lenses (BE Enterprises, Capricornia) targeted to correct +1.50 D, in one eye only. The fellow eye acted as a non-lens wearing control. Lenses were worn overnight over a 7-day period and changes in subjective refraction and corneal topography were measured on lens removal (am) and 8 h after lens removal (pm). After a 2-week washout period, eight subjects repeated the study with the same lens design targeted to correct +3.50 D. Central corneal thickness was measured in this group using an ultrasound pachometer.

There were statistically significant changes from baseline in all variables at all visits in lens wearing eyes. The central cornea steepened, and the mid-peripheral cornea flattened after one night of wear for both refractive targets, with greater effect and greater retention of effect by day 7. The +1.50 D refractive target was reached by day 7. However, the +3.50 D target was not reached, and showed greater variability in outcomes. There was no statistically significant change in central corneal thickness with the +3.50 D target lens at pm visits on days 1 or 7.

The time course of refractive and corneal topographic changes in hyperopic OK is analogous to myopic OK. Most change in refractive and topographic variables occurs on day 1, with regression of effect during the day but greater retention of effect by day 7. Refractive outcomes were less predictable with the +3.50 D compared with the +1.50 D target lens. There was no change from baseline in central corneal thickness at pm visits despite significant retention of OK effect. This suggests that the primary corneal change in hyperopic OK may be mid-peripheral corneal thinning rather than central corneal thickening.