Abstract
BACKGROUND: One of the problems in the diagnosis and treatment of pellucid marginal degeneration of the cornea is the difficulty of systematizing its manifestations due to the lack of classification. This is due to the low frequency of pellucid marginal degeneration in the structure of primary keratectasia, the main type of which is keratoconus. The developed classifications of keratoconus cannot be fully applied to pellucid marginal degeneration.
 AIM: The aim was to develop a classification of pellucid marginal degeneration based on investigation of relationship between functional and refractive changes.
 MATERIALS AND METHODS: The study included 42 people (42 eyes) with pellucid marginal degeneration. Keratometry and refractometry were performed, uncorrected and best corrected visual acuity, as well as cylindrical and spherical components of subjective refraction were studied, and retinal visual acuity was determined. The 1st group 12 patients (12 eyes) with fully corrected induced ametropia (best corrected visual acuity 0.8), the 2nd group 17 patients (17 eyes) with partially corrected induced ametropia (0.8 and 0.3), the 3rd group 13 patients (13 eyes) with uncorrected induced ametropia (0.3).
 RESULTS: To develop a clinical classification of pellucid marginal degeneration by stages, we selected: the values of corneal astigmatism, best corrected visual acuity and Index of difference between the values of maximum and minimum keratometry (K), all of which had good separation of obtained data, and their demarcate values in groups.
 CONCLUSION: The study showed the presence of relationship between functional and refractive changes indices of eyes with pellucid marginal degeneration. The leading parameters of refractive status, objectively determining the value of best corrected visual acuity, are induced corneal astigmatism and K. The developed classification of pellucid marginal degeneration is easy to use and makes it possible to determine the stage of keratectasia even if there is only induced corneal astigmatism or K values.
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