Visual field defects can be a sign of ophthalmic or neurological disease. The area of the visual field affected can help localise the lesion and suggest likely diagnoses. Clinical assessment to identify the basic type of field defect and any associated systemic symptoms will assist GPs in determining the urgency of referral and deciding between ophthalmic or neurological referral.
The average human visual field extends 60 degrees nasally, 90 to 100 degrees laterally and 150 degrees vertically around the central point of vision. The visual fields overlap by approximately 120 degrees, giving stereopsis (depth perception). Visual acuity is sharpest centrally, where the photoreceptors on the retina are closer together, with image resolution and colour perception being reduced in the peripheral visual field.
Visual field problems can be a sign of underlying ophthalmic or neurological disease. Because the retinal ganglion cells travel in a precise anatomical location from the retina to the lateral geniculate nucleus, and the relative positions of the axons are preserved in the optic radiations from this nucleus to the occipital cortex, it is possible to localise abnormalities based on assessment of the visual field (Figure 1).
Picture credit: © Jan Mika/Depositphotos. Model used for illustrative purposes only.