ABC of eyes. Gradual visual loss, partial sight, and "blindness".

Abstract

Radiograph showing calcified meningioma. Note a plain skull radiograph will not show most intracranial tumours. # Refractive error?The pin hole test is a most and drugs useful test for identifying refractive error. If there is a refractive error the vision will improve. If the patient has strong glasses the pin hole should be used with the patient wearing the glasses. Once other causes of visual loss have been excluded, the patient can be sent to the optometrist for refraction. # Cataract?This is probably the commonest cause of gradual visual loss and the diagnosis may be made on viewing the red reflex. The patient should be referred if the visual disturbance interferes appreciably with his lifestyle. If a patient with a cataract cannot project light or has an afferent pupillary defect, however, other diseases must be excluded. # Chronic open angle glaucoma?Unfortunately the patient may not complain of visual disturbance until l?te in the course of the disease, hence the need for screening. Chronic open angle glaucoma should, however, be excluded in any patient complaining of gradual visual loss. Any family history of glaucoma should be elicited. The vision may still be 6/6 so the visual field should be checked with a red pin, and cupping of or asymmetry between the optic discs must be sought. # Senile macular degeneration?This may occur gradually and is typified by loss of the central field. There are usually pigmentary changes at the macula. The disease occurs in both eyes, but it may be asymmetrical, and it is more common in short sighted patients. The gradual deterioration is not treatable, but if acute visual distortion supervenes during the course of the disease there may be a leaking vessel under the retina that may be treated with the laser. # Hereditary degeneration of the retina?This is relatively rare but should be suspected if there is a family history of visual deterioration. Symptoms include intolerance to light and night blindness. Most types of degeneration are not treatable, but some are associated with metabolic disorders and the visual deterioration may be arrested by treatment of the metabolic abnormality. These patients need to be referred for diagnosis, treatment, discussion of prognosis, and genetic counselling and to social services and voluntary organisations. # Compressive lesions of the optic pathways?These are relatively rare, but should always be considered. The history and examination may give clues if there are headaches, focal neurological signs, or endocrinological abnormalities such as acromegaly. There should not be an afferent pupillary defect in most patients with cataract, macular degeneration, or refractive error. Testing of visual fields may show the bitemporal defect of a pituitary tumour. The discs should be checked for optic atrophy and papilloedema. # Drugs?Several drugs may cause visual loss. In particular, a history of excessive alcohol intake or smoking, methanol ingestion, or the taking of chloroquine or ethambutol should lead to a suspicion of drug induced visual deterioration. Systemic steroids may cause cataracts and steroid drops may induce glaucoma.