Neurological disease can involve the eye in many ways. Every structure--the conjunctiva, cornea, anterior chamber, iris, lens, vitreous humour, retina, choroid, and optic nerve--can be affected. In many cases, ocular involvement is the first manifestation of the underlying disease. In such cases, the ability of the physician to recognise the nature and significance of the ocular abnormality can lead to early diagnosis and successful treatment of the underlying condition. In other cases, recognition of the ocular abnormality can prevent permanent visual dysfunction.