Cross-linking may help slow myopia
Research is ongoing in an area with limited treatments available
Cross-linking, better known as a treatment for corneal ectasia, may have a role to play in slowing the development of pathological myopia, according to Mor Dickman, Maastricht University Medical Centre, the Netherlands.
“The sclera is in fact a dynamic tissue capable of alteration, which unfortunately allows myopic progression to occur,” said Dr Dickman at a session of the 36th Congress of the ESCRS in Vienna in September 2018.
His presentation, “Scleral Cross-Linking for Myopia”, was part of an ESCRS Clinical Research Symposium on myopia. Dr Dickman’s research concerns the use of scleral cross-linking to slow or halt the ocular elongation that can lead to pathological myopia.
“The pathophysiology of myopic progression is locally driven. Hyperopic defocus, in which the image is projected ‘behind’ the retina, results in a blurred image on the retina. This optical signal elicits a chemical signal, which then results in a mechanical response in the sclera, namely ocular elongation.”
So, what are the changes that we see in the scleral microstructure of highly myopic eyes as compared to controls? Increased extracellular matrix modelling, decreased intramolecular cross-links, biomechanical weakening as well as myofibroblast differentiation are involved. These all seem to play a significant role in axial length progression, he explained.
However, this biomechanical weakening, and thus elongation, might be counteracted by collagen cross-linking, a technique that is currently used to treat corneal abnormalities such as keratoconus and ectasia.
“Cross-linking normally plays an important role in stabilising the hierarchical structure of the sclera, both during development and ageing. The scleral cross-linking that is seen with age may explain the arrest of myopic progression in later life. The goal of cross-linking the collagen would be to address this mechanical deficiency prior to the development of chorioretinal pathology,” said Dr Dickman.
Dr Dickman’s team has tested the technique in rabbit models. Both riboflavin and genipin have been shown to be effective.
“We used atomic force microscopy and strip extensiometry to demonstrate that scleral cross-linking increases the strength of both internal and external sclera in rabbits. This led to effective arrest of axial elongation,” he reported.
Dr Dickman is currently working on improving the safety of the technique, particularly with regards to potential side-effects such as retinal toxicity.
The disadvantage of this approach, however, is that it is an invasive treatment for disease prevention that might interfere with normal development. Further, the sclera itself his limited accessibility and visualisation, making treatment less straightforward than cross-linking the cornea.
Nevertheless, there are limited effective treatment alternatives and this modality is less invasive than retinal surgery techniques. Research is ongoing.