Refractometry after different methods of corneal reshaping

Purpose: development of a method for determining refraction in patients with altered topography of the anterior surface of the cornea.

Material and methods. The study was performed in 57 patients (114 eyes) aged 12–30 years with mild and moderate myopia, corrected by various methods: bifocal soft contact lenses (BSCL) (40 eyes), orthokeratologic (OK) lenses (30 eyes), LASIK (22 eyes), photorefractive keratectomy (22 eyes). All patients had their refraction measured using three methods: standard autorefractometry (without cycloplegia) (Tonoref III, Nidek, Japan), OPD Scan III aberrometer (Nidek, Japan) with determination of the spherical equivalent of refraction (defocus), as well as the smallest local refraction value within the pupillary zone on the vergence map (OPD). Then a duochrome test was performed (in steps of 0.25 D) with the presentation of optotypes on a red and green background. The power of the additional lens, which equally improves visual acuity on green and red backgrounds, corresponded to the clinical refraction of the eye in the BSCL, after OK correction or other types of corneal reshaping.

Results. Refractometry after OK reshaping of the cornea and in the worn BSCL gives incorrect, overestimated results in the direction of myopia. After excimer laser correction of myopia, the data of various autorefractometry methods coincide with each other and with subjective refraction. A combined method for determining refraction in patients with altered topography of the anterior surface of the cornea has been developed, consisting in a combination of two methods – aberrometry with the detection of the lowest refraction value in the pupil area and a duochromic test with correction of the obtained refraction value.

Conclusion. The developed method allows obtaining the most adequate refractive indices for users of bifocal, multifocal contact and OK lenses for myopia correction.

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