All those, therefore, who have cataract see the light more or less, and by this we distinguish cataract from amaurosis and glaucoma, for persons affected with these complaints do not perceive the light at all. Paul of Aegina (615–690)
The commonest cause of visual dysfunction is a simple refractive error. However, there are many causes of visual failure, including the emergency of sudden blindness, a problem that requires a sound management strategy. Apart from migraine, virtually all cases of sudden loss of vision require urgent treatment.
The ‘white’ eye or uninflamed eye presents a different clinical problem from the red or inflamed eye.1 The ‘white’ eye is painless and usually presents with visual symptoms and it is in the ‘white’ eye that the majority of blinding conditions occur.
Criteria for blindness and driving
This varies from country to country. The WHO defines blindness as ‘best visual acuity less than 3/60’, while in Australia eligibility for the blind pension is ‘bilateral corrected visual acuity less than 6/60 or significant visual field loss’ (e.g. a patient can have 6/6 vision but severely restricted fields caused by chronic open-angle glaucoma). The minimum standard for driving is 6/12 (Snellen system).
Key facts and checkpoints
The commonest cause of blindness in the world is trachoma. The other major causes of gradual blindness are cataracts, onchocerciasis and vitamin A deficiency.2
In Western countries the commonest causes are senile cataract, glaucoma, age-related macular degeneration, trauma and the retinopathy of diabetes mellitus.2
The commonest causes of sudden visual loss are transient occlusion of the retinal artery (amaurosis fugax) and migraine.3
‘Flashing lights’ are caused by traction on the retina and may have a serious connotation: the commonest cause is vitreoretinal traction, which is a classic cause of retinal detachment.
The presence of floaters or ‘blobs’ in the visual fields indicates pigment in the vitreous: causes include vitreous haemorrhage and vitreous detachment.
Posterior vitreous detachment is the commonest cause of the acute onset of floaters, especially with advancing age.
Retinal detachment has a tendency to occur in short-sighted (myopic) people.
Suspect a macular abnormality where objects look smaller or straight lines are bent or distorted.
The history should carefully define the onset, progress, duration, offset and the extent of visual loss. An accurate history is important because a longstanding visual defect may only just have been noticed by the patient, especially if it is unilateral. Two questions need to be answered:
The distinction between central and peripheral visual loss is useful. Central visual loss presents as impairment of visual acuity and implies defective retinal image formation (through refractive error or opacity in the ocular ...