To report one case of duck phenotype keratoconus treated with a new model of asymmetric intrastromal corneal ring segments (ICRS) with variable thickness and base width.

Keratoconus is an uncommon corneal disorder where the central cornea undergoes progressive thinning and steepening causing irregular astigmatism. Treatment goals are to provide functional visual acuity and halt changes in the corneal shape if progressing. ICRS are placed in the mid-corneal peripheral stroma at approximately two-thirds of depth outside the central optical zone to reshape the anterior corneal surface while maintaining the prolate profile of the cornea and producing an arc shortening effect that is proportional to the thickness of the device. This technique requires no removal of corneal tissue, no intraocular incision, and leaves the central cornea untouched. The advent of asymmetric ICRS with progressive thickness and width brings new possibilities.

Clinical case presentation.

A 22-year-old male presented with complaints of progressive decreased visual acuity for 7 years. No relevant personal history, except for eye rubbing. Left eye (OS) best corrected visual acuity (BCVA) was 1.0 logMAR. Scheimplfug tomography using Pentacam revealed low asphericity, irregular astigmatism and not coincident topographic and coma axes. The topographic pattern had the typical duck morphology. Mean and steepest keratometric values were 48.6D and 50.8D, respectively. He underwent OS implantation of ICRS of variable thickness and base width, 150 to 250 µm, with 120º of arc, implanted at topographic axis, and with the thicker end embracing coma. Two and a half months after the procedure OS BCVA was 0.3 logMAR. Mean and steepest keratometric values were 46.6D and 47.8D, respectively. No serious implant-related complications occurred during the follow-up.

The implantation of asymmetric ICRS induces a significant anterior corneal flattening (leading to refractive changes), reduction of its prolate shape and irregularity, and improvement in patient BCVA. To correct duck phenotype keratoconus the asymmetric ICRS should be implanted at topographic axis, and with the thicker end embracing coma, obtaining a customized correction of both problems, topographic astigmatism, and coma. Each keratoconus phenotype should have a specific correction strategy with asymmetric ICRS.