Cataract and retinopathy: Screening for treatable retinopathy

Diabetes causes cataract and certain physical changes in the lens. The diabetic lens is larger than the non-diabetic and shows greater light scatter and fluorescence. Both hyperglycaemia and lowering of blood glucose cause refractive changes and hypermetropia is the most common. Classical ‘snow-flake’ juvenile cataract associated with hyperglycaemia is now rare. It has an osmotic mechanism. Diabetes is a risk factor for cataract in adults which is duration dependent, more frequent in women and leads to earlier surgery. It resembles non-diabetic senile cataract. Extracapsular cataract extraction is the method of choice for diabetic cataract with a better visual result and less risk of rubeosis iridis. A posterior chamber implant may still permit retinal photocoagulation if necessary.

Diabetic retinopathy is still the leading cause of blindness in the working age group. The beneficial effect of photocoagulation has been shown by randomized controlled trials to be long-lasting for both proliferative retinopathy and maculopathy. Therefore there is a need for screening, especially for those with proliferative disease which may be present without symptoms. A knowledge of risk factors will enhance detection rate with duration as the strongest determinant for retinopathy.

Any screening modality should be highly sensitive as well as specific. The role of different professionals as potential screeners should be considered.

Adequate provisions include facilities for checking vision and for dimming ambient lighting. Mydriasis and a good ophthalmoscope light will increase detection rate.

The use of a 45° non-mydriatic camera is unlikely to supplant the use of an ophthalmoscope as a single field is likely to miss important lesions.

A 60° camera may confer a large enough field and the use of transparencies will provide magnification when films are projected but the camera is more difficult to use.

A list of features chosen by a recent study to characterize sight-threatening retinopathy is included and their presence indicates the need for referral to an ophthalmic clinic for treatment or close observation.