Scleral remodelling in myopia and its manipulation: a review of recent advances in scleral strengthening and myopia control

Simon Backhouse,Alex Gentle

doi:10.21037/aes.2018.01.04

Abstract

The biological mechanisms of eye growth and refractive development are increasingly well characterised, a result of many careful studies that have been carried out over many years. As the outer coat of the eye, the sclera has the ultimate impact on the restraint or facilitation of eye growth, thus any changes in its biochemistry, ultrastructure, gross morphology and/or biomechanical properties are critical in refractive error development and, in particular, the development of myopia. The current review briefly revisits our basic understanding of the structure and biomechanics of the sclera and how these are regulated and modified during eye growth and myopia development. The review then applies this knowledge in considering recent advances in our understanding of how the mechanisms of scleral remodelling may be manipulated or controlled, in order to constrain eye growth and limit the development of myopia, in particular the higher degrees of myopia that lead to vision loss and blindness. In doing so, the review specifically considers recent approaches to the strengthening of the sclera, through collagen cross-linking, scleral transplantation, implantation or injection of biomaterials, or the direct therapeutic targeting and manipulation of the biochemical mechanisms known to be involved in myopia development. These latest approaches to the control of scleral changes in myopia are, where possible, placed in the context of our understanding of scleral biology, in order to bring a more complete understanding of current and future therapeutic interventions in myopia, and their consequences.

Highlights

The sclera is a specialised connective tissue that accounts for the majority of the surface area of the outer coat of the eye
TGF-β1 and FGF-2 levels in the transition zone between host and donor tissue are significantly increased via mechanical stretching, suggesting enhanced fusion and thickening of the Posterior scleral reinforcement (PSR) region occurs under mechanical forces. These findings suggest that the increasing scleral elastic modulus seen following PSR is a function of induced tissue remodelling beneath the donor tissue that is the reverse of that seen during the development of myopia
The changes that occur in the sclera during myopia development represent a complex interaction between tissue remodelling, synthesis, and degradation, the upshot of which is a reduction in scleral stiffness and increased extensibility of the posterior sclera

Summary

Introduction

The sclera is a specialised connective tissue that accounts for the majority of the surface area of the outer coat of the eye. Studies in post mortem, highly myopic human eyes have confirmed that the active scleral tissue loss is a result of collagen and, to a lesser degree, mucopolysaccharide depletion [21], animal models have shown this to be a complex process, involving both accelerated scleral matrix degradation and slowed production of new extracellular matrix as an eye becomes myopic [13].

Results

Conclusion