Predictive Model Of The Short-Term Effect Of Myopic Orthokeratology

To establish a pattern of corneal epithelial thickness modifications correlated with topographic and refractive
changes after orthokeratology (OK) for myopia, and to propose a predicting equation of the OK effect according to the
wearing time, and changes in refraction and corneal shape.

Department of Optics, Pharmacology and Anatomy, University of Alicante, Spain; Vithas Medimar International
Hospital, Alicante, Spain; Department of Ophthalmology, Torrecárdenas Hospital Complex, Almería, Spain; University of
Bern, Bern, Switzerland.

A prospective study included 50 myopic eyes undergoing orthokeratology. Refractive, corneal topographic and
aberrometry, and corneal epithelium thickness were evaluated from the first 20 minutes of contact lens wear to 1 week
of OK use. Central epithelium thickness (CET), para-central epithelium thickness (PCET) at 2 mm from the center, and
mid-periphery epithelium thickness (MPET) at 4 mm from the center were measured by a spectral domain optical
coherence tomography (OCT). To establish a predicting equation of such OK effect, a multiple linear regression analysis
was used relating baseline data and the change in refraction and the other parameters evaluated during these first 60
minutes with the OK effect at one week.

All clinical parameters evaluated showed a statistically significant change (p<0.001) in all visits, except the
coefficient of coma aberration, which showed a statistically significant change only after one week of use (p<0.05). CET
thinned from the first 40 minutes of OK use with statistical significance (p<0.001), with a difference in means at one week of
use of 8.06 ± 0.78. PCET showed only a significant thinning after one week (4.53±1.03, p<0.001). MPET did not show a
statistically significant change. With multiple linear regression analysis, a predicting model of the effect of OK at one week
was obtained (R2= 0.718), which was based on baseline refraction, baseline keratometry, age, and refractive change after
one hour of lens use.

Orthokeratology for myopia induces a significant thinning of CET from the first 40 min of contact lens wear.
This thinning remained constant for one week, including the paracentral area of the cornea. The refraction change
achieved with OK in the short term can be predicted from baseline spherical equivalent and keratometry, age and the
refractive changes that occur after 1 hour of OK use.