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Clinical assessment remains the crucial step in management of disorders of the anterior visual pathways. Once the patient has been examined, or in the majority of cases once the history has been obtained, the clinician should have a clear idea of the site of the disease process and its likely pathogenesis. Only then can appropriate and timely investigations be organised and their results interpreted correctly.
DISTINGUISHING BETWEEN RETINAL AND OPTIC NERVE DISEASE
Although fundal examination is diagnostic in many patients with retinal disease (see fig 7 in Lueck et al, p iv9), initial assessment by optometrists generally results in such patients being referred to ophthalmologists. In neuro-ophthalmic practice fundal abnormalities are usually absent or non-specific, such that other clinical features must be relied upon. They may be subtle so requesting repeat examination by an ophthalmologist may be helpful when other clinical features indicate retinal disease.
Photopsia (flashes or sparks of light) are most commonly caused by vitreo-retinal traction, in which case they are often induced by eye movements and do not last for more that a few weeks. Persistent photopsia are a feature of retinal disease, either degenerative, inflammatory (for example, acute zonal occult outer retinopathy (AZOOR) that characteristically presents acutely with unilateral visual field loss, photopsia, and normal fundal examination but abnormal electroretinograms (ERGs)), or paraneoplastic (cancer or melanoma associated retinopathy). Photopsia induced by eye movements or change in illumination occasionally occur in optic nerve disease. Metamorphopsia and micropsia (distortion and minification of the visual image) most commonly indicate retinal disease, respectively caused by retinal distortion and separation of photoreceptors by oedema. (Particularly photopsia but also metamorphopsia can occur in posterior visual pathway disease.) Night blindness (nyctalopia) indicates rod photoreceptor dysfunction, characteristically occurring in retinitis pigmentosa but also in melanoma associated retinopathy. Light intolerance (“day blindness” or hemeralopia) is a feature of cone photoreceptor dysfunction. …