Presenter – DAVID WILLIAMS, MA, VetMB, PhD, CertVOphthal, CertWEL, FHEA, FRCVS

One of the beauties of the eye is the transparency of the cornea and lens. The collagen fibrils of the cornea are all around 20nm in diameter and 20nm apart, so light, with a wavelength over 20 times that dimension, passes straight through. The same is true of the lens crystallin proteins, highly regular with a similar individual size. In both these cases, a loss of regularity leads to translucency or complete opacity. When excess water enters the cornea, the collagen fibrils are irregularly separated from each other, giving the classic ground glass appearance of corneal oedema. When crystallins in the lens aggregate together, or when excess water enters the lens as in diabetic cataract, the clear transparency that allows the lens to be known as “biological glass” is lost. We need to understand the causes and processes behind this excess water in order to stop, or even reverse, the problem. Corneal oedema often occurs with endothelial dysfunction, either from dystrophy, degeneration or damage in glaucoma. Sudden opacity of the lens may occur in diabetes where excess glucose is changed to the alcohol sorbitol with disastrous osmotic effects drawing water into the lens. Another cause of sudden cataract can be trauma while more gradual changes in the lens occur through crystallin aggregation through photo-oxidation of thiol groups turning to di-sulphide bridges. Getting to grips with these degenerative processes may allow us to prevent cataract both in companion animals and in humans as well where cataracts blind millions of people.

Lecturer DAVID WILLIAMS, MA, VetMB, PhD, CertVOphthal, CertWEL, FHEA, FRCVS. he is now associate lecturer in veterinary ophthalmology in the Department of Clinical Veterinary Medicine in Cambridge, a position he combines with teaching at St John’s College, where he is fellow, director of studies in veterinary medicine and college lecturer in pathology.

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