The terms below explain field loss. I have several friends who have vision loss due to illness. One has MS, one had a stoke and one had three brain aneurysms. She is a close friend and we tease her because she still drives but can't see one fourth of the field in both eyes.
A person’s visual field is the most important single factor affecting visual function. There is an increased number of patients with visual impairment, secondary to visual field loss alone or in conjunction with decreased visual acuity. This is mainly due to the increased survival rate of head trauma and stroke patients. A problem exists only when the field loss involves both eyes. If the field loss is in one eye only, it will be covered by the other eye. These patients need a combination of optical intervention along with mobility instruction.
There are two general types of field defects:
Overall constriction
Usually caused by advanced ocular disease such as retinal degeneration’s (retinitis pigmentosa) and optic nerve disease (glaucoma).
Hemispheric field loss
Usually due to a stroke or head injury. While a person with a visual field loss may have near normal visual acuity, the visual field loss may make walking in a crowd difficult because the ground cannot be seen. A visual field loss may also make reading difficult because the beginning or end of a sentence cannot be seen. Special glasses with prisms can be made to help a patient become more aware of their lost visual field, making navigation and reading easier. A low vision optometrist prescribes this type of eyeglasses.
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