[Topographical evaluation on decentration of orthokeratology lenses]

To evaluate the degree and correlative factors of decentration of orthokeratology lenses and its effect on the visual function.

Two different kinds of orthokeratology lenses were fitted to 270 eyes of 135 patients [initial mean refractive error: (-3.98 +/- 1.51) D]. Humphery Instruments ATLAS 8.0 was used for the computer-assisted analysis of corneal differential topographical maps. The examination of corneal topography was proceeded on the patients before the fitting of orthokeratology lenses and 6-month later. The distance from center of optic zone to apex of the cornea was measured as the value of decentration of orthokeratology lenses. The factors influenced the value of decentration were analyzed, including the initial refraction error, astigmatism, keratometry values, corneal eccentricity, and the diameter of the lens. The complaints of patients were recorded. Questionnaires, involving the symptoms of monocular diplopia and glare, were used to evaluate the effects of decentration of orthokeratology lenses on the visual function.

The mean distance of decentration was (0.49 +/- 0.34) mm after one night fitting, the mean distance of decentration after follow-up for 1 month, 3 months and 6 months was (0.57 +/- 0.41) mm, (0.55 +/- 0.48) mm and (0.59 +/- 0.39) mm, respectively. After one month, the distance of decentration was less than 0.5 mm in 51.1% eyes, 0.5 - 1.0 mm in 35.6% eyes and more than 1.0 mm in 13.3% eyes. The direction of decentration in eyes with more than 0.50 mm decentration was mainly in the temporal side (48.5%). Patients with greater initial astigmatism and smaller diameter of lens showed greater distance of decentration (P < 0.05). There was no statistically significant difference in the distance of decentration between two groups with different corneal eccentricities and keratometry values (P > 0.05). The distance of decentration was greater in patients with monocular diplopia and glare.

The degree of decentration of orthokeratology depends on the degree of initial refractive error, astigmatism and the design of orthokeratology lenses. The degree of decentration can influence the visual function.