Research Highlights

Ring segments in the eye to improve vision

Published online 17 September 2009

Mohammed Yahia

Pellucid marginal degeneration (PMD) is an idiopathic disorder, in which thinning of the eye cornea occurs in a crescent-shaped pattern. While it is usually asymptomatic, progressive deterioration in uncorrected and best-corrected visual acuity can occur in advanced cases.

Several treatments for PMD have been suggested, among them intracorneal ring segment (ICRS) implantation. In the altered form of the cornea in PMD, the addition of extra material creates a change in corneal asymmetry and refraction, which may lead to an improvement in visual acuity. Researchers from Spain, Egypt and Turkey conducted a retrospective study on 15 PMD patients 6 months after undergoing ICRS implantation.

Researchers found an average reduction in astigmatism of 50% after surgery. The best spectacle-corrected visual acuity (BSCVA) improved after the operation by more than two lines on the eye chart. No severe complications were observed during the checkup.

However, researchers suggest that patients with a high degree of astigmatism before the operation usually show poorer results afterwards. This may be related to a specific corneal structure associated with the progression of the disease that limits the effect of the ring segments. These limiting factors should be taken into account before the ICRS implantation to make the surgery worthwhile.

The researchers also suggest that future studies should look at ICRS implantations in cases of PMD in the longer term to determine which factors are involved in the predictability and the stability of this therapeutic modality.


  1. Piñero, D. P. et al. Refractive and Corneal Aberrometric Changes after Intracorneal Ring Implantation in Corneas with Pellucid Marginal Degeneration. Ophthalmology 116, 1656-1664 (2009)  | Article | PubMed