The anterior scleral thickness in primary open-angle glaucoma with high myopia

To determine the association between myopia and open-angle glaucoma. Systematic review and meta-analysis of observational studies. Thirteen studies involving 48 161 individuals. Articles published between 1994 and 2010 were identified in PubMed, Embase, and reference lists. Study-specific odds ratios (ORs) were pooled using a random effects model. Odds ratios with 95% confidence intervals (CIs) of myopia as a risk factor for open-angle glaucoma. Data from 11 population-based cross-sectional studies were included in the main analyses. The pooled OR of the association between myopia and glaucoma based on 11 risk estimates was 1.92 (95% CI, 1.54-2.38). On the basis of 7 risk estimates, the pooled ORs of the associations between low myopia (myopia up to -3 D) and glaucoma and between high myopia (≤-3 D myopic) and glaucoma were 1.65 (1.26-2.17) and 2.46 (1.93-3.15), respectively. There was considerable heterogeneity among studies that reported an association between any myopia and glaucoma (I(2)=53%) and low myopia and glaucoma (I(2)=29%), but not for high myopia and glaucoma (I(2)=0%). After omitting studies that contributed significantly to the heterogeneity, the pooled ORs were 1.88 (1.60-2.20) for any myopia and glaucoma and 1.77 (1.41-2.23) for low myopia and glaucoma. Individuals with myopia have an increased risk of developing open-angle glaucoma. The author(s) have no proprietary or commercial interest in any materials discussed in this article. Copyright © 2011 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved. Show more

Myopia is one of the most prevalent ocular conditions and is the result of a mismatch between the power of the eye and axial length of the eye. As a result images of distant objects are brought to a focus in front of the retina resulting in blurred vision. In the vast majority of cases the structural cause of myopia is an excessive axial length of the eye, or more specifically the vitreous chamber depth. In about 2% of the general population, the degree of myopia is above 6 dioptres (D) and is termed high myopia. The prevalence of sight-threatening ocular pathology is markedly increased in eyes with high degrees of myopia ( > -6 D). This results from the excessive axial elongation of the eye which, by necessity, must involve the outer coat of the eye, the sclera. Consequently, high myopia is reported as a leading cause of registered blindness and partial sight. Current theories of refractive development acknowledge the pivotal role of the sclera in the control of eye size and the development of myopia. This review considers the major biochemical mechanisms that underlie the normal development of the mammalian sclera and how the scleral structure influences the rate of eye growth during development. The review will characterise the aberrant mechanisms of scleral remodelling which underlie the development of myopia. In describing these mechanisms we highlight how certain critical events in both the early and later stages of myopia development lead to scleral thinning, the loss of scleral tissue, the weakening of the scleral mechanical properties and, ultimately, to the development of posterior staphyloma. This review aims to build on existing models to illustrate that the prevention of aberrant scleral remodelling must be the goal of any long-term therapy for the amelioration of the permanent vision loss associated with high myopia. Show more

The objective of this study was to measure the biomechanical response of the human posterior sclera in vitro and to estimate the effects of age and glaucoma. Scleral specimens from 22 donors with no history of glaucoma and 11 donors with a history of glaucoma were excised 3 mm posterior to the equator and affixed to an inflation chamber. Optic nerve cross-sections were graded to determine the presence of axon loss. The time-dependent inflation response was measured in a series of pressure-controlled load-unload tests to 30 mm Hg and creep tests to 15 and 30 mm Hg. Circumferential and meridional strains were computed from the digital image correlation displacements, and midposterior stresses were determined from pressure and deformed geometry. Among normal specimens, older age was predictive of a stiffer response and a thinner sclera. In the age group 75 to 93, diagnosed glaucoma eyes with axon damage were thicker than normal eyes. Both damaged and undamaged glaucoma eyes had a different strain response in the peripapillary sclera characterized by a stiffer meridional response. Undamaged glaucoma eyes had slower circumferential creep rates in the peripapillary sclera than normal eyes. Glaucoma eyes were not different from normal eyes in stresses and strains in the midposterior sclera. The observed differences in the biomechanical response of normal and glaucoma sclera may represent baseline properties that contribute to axon damage, or may be characteristics that result from glaucomatous disease. Show more