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New keratoconus classification guides customization of intracorneal ring segment implantation
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OVIEDO, Spain — A new keratoconus classification oriented to the implantation of intracorneal ring segments was presented at the second European Meeting of Young Ophthalmologists.
“Our classification is aimed at using Ferrara rings and originates from Ferrara’s morphological classification. It is based on ectasia location and uses asphericity, topographic astigmatic patterns and the relationship between topographic, comatic and refractive axis as parameters,” Luis Fernández-Vega, MD, said.
Luis Fernández-Vega
Using pachymetry maps, the thinnest point of the cornea is located, and the distance from the center of the pupil is measured. This measurement is used to classify the keratoconus as central, paracentral or pericentral.
“Looking at the curvature, we can then determine the flattest topographic axis and the magnitude of astigmatism. The elevation map provides the asphericity value, very important to establish treatment. Finally, coma and spherical aberration are assessed on aberrometric map,” Fernández-Vega said.
By relating all these parameters, a more advanced classification than the Ferrara was achieved, leading to five main phenotypes: three of them paracentral — respectively with coincident, non-coincident, and perpendicular topographic and comatic axis — and two central — respectively with high asphericity and with regular topographic astigmatism.
The five phenotypes are associated, in the same order, with the “croissant,” “duck,” “snowman,” “nipple” and “bow tie” topographic patterns.
This system was used to classify more than 1,200 keratoconus cases. Most were paracentral or pericentral, most had low asphericity, and the majority had irregular astigmatism. The most common were phenotype 1 (35%) and 2 (32%), followed by snowman (17%), nipple (6%) and bow tie (3%).
“These were 93% of our sample. The other 7% were central keratoconus without high asphericity but irregular astigmatism,” Fernández-Vega said.
“These phenotypes are completely different from one another and required a customized use of ICRS,” Fernandez-Vega said. – by Michela Cimberle
Reference:
Fernández-Vega L. Classification of keratoconus. Presented at: European Meeting of Young Ophthalmologists; June 24, 2016; Oviedo, Spain.
Disclosure: Fernández-Vega reports no relevant financial disclosures.