Potential new treatment
Tackling myopia via scleral cross-linking
Scleral cross-linking is a potentially promising new treatment modality for pathological myopia that may in the future help to avoid complications associated with more severe forms of the condition, according to Mor Dickman MD, PhD.
“Studies have shown that cross-linking is effective in stiffening the sclera ex vivo and arresting axial elongation in myopia animal models in vivo, with optimised protocols showing promise with regard to retinal safety,” he said at the online 38th Congress of the ESCRS.
Despite its potential, Dr Dickman, Maastricht University Medical Centre, the Netherlands, acknowledged that scleral cross-linking has several substantial hurdles to overcome if it is ever to be adopted as a viable treatment for myopia.
“Scleral cross-linking may interfere with the development of the eye, especially in children, and may also cause glaucoma if it is not restricted. There is also no back-up procedure available in case of failure, which is the equivalent to a penetrating keratoplasty for corneal cross-linking,” he added.
The rationale for targeting the sclera stems from studies showing that the development of high myopia is associated with thinning of the posterior sclera and changes in the collagen fibrils.
“The total scleral volume remains unchanged and the biomechanically weakened sclera expands even under normal intraocular pressure, enlarging the posterior segment of the eye and further weakening the sclera. The process results in a vicious circle, which weakens the sclera and increases the myopia,” explained Dr Dickman.
The key challenge is to target the appropriate part of the sclera with any cross-linking treatment, said Dr Dickman.
“When the entire sclera is treated the increased stiffness can cause glaucoma. Restricting scleral stiffness to a localised region can actually decrease the risk of glaucoma and act as a neuroprotective therapy by reducing local biomechanical stress on the optic nerve,” he said.
With this goal in mind, Dr Dickman and colleagues together with the group of Professor Avigdor Scherz and Dr Arie Marcovich from the Weizmann Institute in Israel developed a novel CXL technique combing light-sensitive WST11 (Tookad) and near infrared (NIR) light.
“Together we have shown that this technique results in a safe and effective long-term corneal stiffening in vivo. Upon illumination with near infrared light of 750nm, which has deep tissue penetration and is non-toxic to the retina, WST11 releases free radicals that result in collagen cross-linking. It is possible to deliver the drug via sub-tenon’s injection and activate it in the designated treatment area using NIR that is delivered via the pupil to reach the sclera,” said Dr Dickman.
He added that further studies, such as those being carried out by Dr Craig Boote, Cardiff University, UK, and Prof Sally McFadden, University of Newcastle University, Australia, are needed to determine the long-term in vivo safety and efficacy of the technique.