Light scatter changes due to corneal oedema and contact lens wear

Abstract

G LARE disability can be a problem for contact lens wearers. 1-5 It is caused by a reduction in contrast of the retinal image due to a veiling luminance caused by light scatter within the eye. ~,7 Most of the early studies on glare disability in polymethylmethacrylate (PMMA) contact lens wearers found a reduction in visual performance due to light scatter caused by both epithelial and stromal oedema. 1,2 In the early stages of contact lens wear, the increased lacrimation produces osmotic stress leading to epithelial oedema, s,9 Epithelial oedema can be characterised by large increases in forward scattering of light 1° and is considered to be more visually disabling than is stromal oedema. 11,12 As adaptation to the contact lens occurs, potential epithelial osmotic stress is r educed20edematous changes in adapted lens wearers are more likely to be hypoxic in origin2 Although the main corneal change due to hypoxia is stromal oedema, any significant increases in light scatter due to hypoxia are thought to be due to small epithelial changes. ~3 Glare disability has become less of a problem with the increased use of rigid gas permeable (RGP) and hydrophilic lens materials. 14,15 Recently, Applegate and Wolff measured glare disability in hydrophilic contact lens wearers. Using a sample of five subjects they showed that disability glare was increased with contact lenses as compared to the equivalent spectacle correction. They suggested that this may be due to either the contact lens materials, lens deposits, or corneal oedema. However, a follow-up study by Applegate and Jones 4, using 12 subjects, found more variable results. Some subjects showed an increase in glare disability, some a decrease, and some no change. They concluded that glare disability is not a problem for all lens wearers and suggested that this was consistent with the clinical impressions of patients who reported glare problems. They suggest that disability glare in these subjects may be correlated to the contact lens material or the amount of lens deposit. Backward light scatter is the light scattered back from the ocular media, which can be seen using a slit-lamp. It is more important to measure forward light scatter, however, as it is forward scatter that