Crosslinking of Thin Corneas: a Modern Vision of the Problem. Literature Review

Abstract

Ultraviolet crosslinking is a pathogenetically oriented method of treating primary and secondary corneal ectasias that cause irregular astigmatism and visual impairment. Advanced stage of the disease, when the initial thickness of the cornea is below 400 mc, is a contraindication to the use of the standard «Dresden» protocol of the procedure. In such cases, it is possible to use modified UV crosslinking protocols. This article presents the modern crosslinking methods used for progressive keratoconus in advanced stages with a thin cornea. The presented methods are combined taking into account principled approaches – using additional tools and without them. Both approaches are based on a temporary artificial increase in the thickness of the cornea during the procedure in order to reduce the likelihood of damage to the deep layers of the cornea. The evolution of crosslinking protocols for thin corneas began with the use of hypoosmolar solutions that increase the thickness of the cornea to safe values. However, such an approach was not stable and the change in pachymetry parameters during the procedure created difficulties in its standardization. The use of different staff to increase the thickness of the cornea by providing an additional layer like a contact or biological lens seemed more encouraging. At the same time, the low permeability of these additional layers to oxygen, much needed for the UV crosslinking process of macromolecules, limited the overall effectiveness of the procedure. As a result of the progressive development of technologies and the improvement of devices, the logical continuation of the trend of modifying the crosslinking protocol was the introduction of an individual approach to customization of the protocol. The described modified protocols, taking into account the different principles of the surgical approach in ultraviolet radiation, set forth the results, evaluate their effectiveness and safety when applied to patients with a thin cornea.

Keywords

• crosslinking
• uv irradiation
• keratoconus
• thin cornea