Defects In The Visual Field

Visual field defect means loss of part of the normal area of vision in one or both eyes. The defects usually appear gradually and often remain unnoticed.

The condition may take different forms, from loss of peripheral vision to small blind spots to loss of most of the visual field. Sometimes the patient may have abnormality and bump into objects on one side only or sometimes he may miss the whole section of text while reading.

Causes

Visual field defects may result due to damage to retina, optic nerve or the parts of the brain involved with vision.

Important causes of visual field defects include inflammation of the optic nerve, pituitary tumour, brain damage due to stroke or tumour or abscess, chronic glaucoma and drugs like cyclosporin. Migraine can also cause temporary visual field defects.

The gradual decrease in fluid pressure in the eye in glaucoma can damage the nerve fibres in the retina, causing loss of peripheral vision. That is why, in untreated cases of glaucoma, tunnel vision is left (meaning only a straight narrow area of the central vision). Pituitary tumour often causes loss of outer half of the vision field in each eye. Brain damage may result in loss of one half (right or left) of the visual field in both eyes.

Constricted visual field may be found in conditions such as retinitis, end-stage glaucoma, vitamin A deficiency, hysteria etc.

Diagnosis

The visual field loss must be differentiated from defects with chiasmal visual field defects such as pituitary tumour, meningioma, glioma, trauma, infection and other rare tumours.

Majority of the visual field defects can be detected during routine vision tests to assess the pattern and extent of the defect. Computerized visual field analysis is also useful along with other tests like finger confrontation test, hat-pin confrontation test and amsler grid chart test.

Treatment

The treatment depends upon the underlying cause. All necessary steps must be taken to control the cause such as glaucoma.

Prognosis

The existing defects are usually permanent but treatment of the underlying condition may prevent further deterioration. People generally become used to such defects but it may affect their lifestyle and occupation. In tunnel vision, the patient is advised not to drive.