Purpose: To investigate the mechanism underlying hyperopic orthokeratology (OK) by comparing the short-term clinical effect of lenses before and after central lens fenestration.
Methods: Twelve subjects (age 21 to 24 years) were fitted with rigid hyperopic OK lenses (BE Enterprises/Capricornia) in one eye only. The fellow eye acted as a non-lens wearing control. Lens specifications were matched to provide the same post lens tear film profile in all subjects. Non-fenestrated lenses were worn in the open eye for 1 h and in the closed eye for four nights. Subjective spherical equivalent refraction and corneal topography (Medmont E300) were measured at baseline, after 1 h of lens wear, and within 1 h of waking on days 1 and 4 of overnight lens wear. The lenses were then sent for three 0.75 mm fenestrations within the central optic zone, and lens wearing and measurement procedures were repeated.
Results: There was a statistically significant change from baseline in all variables at all visits in lens wearing eyes. Refraction changed after 1 h of lens wear, with greater effect after overnight wear. Para-central corneal flattening was apparent after 1 h of lens wear, with greater flattening after overnight wear. Central corneal steepening was only statistically significant after overnight wear. Central fenestrations did not lead to a difference in clinical effect in any variables. However, a correlation between apical corneal curvature change and refractive change became apparent only after lens fenestration.
Conclusion: A hyperopic OK effect was established after 1 h with increased effect with longer lens wearing time. Central fenestrations did not affect the clinical outcomes, indicating that corneal compression by the lens in the para-central region as opposed to central post lens tear film suction may be the primary mechanism behind the hyperopic OK clinical effect.