The span of one’s space around him that falls within the vision of the subject at one given time is called field of vision.
1. Visual Field
Visual field span is in all 4 directions but to a different extent in each direction. Its temporal extent is 90 degrees, inferior extent is 70 degrees, nasal extent is 60 degrees and superior extent is 50 degrees.
2. Visual Field Defects:
Any spots of blindness or impaired vision whether located in the center (due to defect or disease in optic disc or nerve) or periphery (due to defect in visual pathways from optic chiasm to proximally onward to visual cortex) of field of vision are called visual field defects.
3. Causes of Visual Field Defects:
Visual field defects can be either central visual field defects or peripheral visual field defects and so are causes of visual field defects i.e. causes of central visual field defects and causes of peripheral visual field defects.
A. Causes of Central Visual Field Defects:
Central visual field defects are caused by defects in macula and diseases of optic nerve. Macular causes include age-related macular degeneration and macular holes. Optic nerve diseases and defects that cause central visual field defects include optic neuropathy and Leber’s optic atrophy. Cone dystrophies can also lead to development of central visual field defects. There are some rare causes of central defects in field of vision, which include Best’s disease, Stargardt’s disease and achromatopsia.
B. Causes of Peripheral Visual Field Defects:
Peripheral visual field defects result from diseases and disorders of retina. Diseases and disorders of retina that cause defects in peripheral field of vision include angle-closure glaucoma, open angle glaucoma, retinal detachment, retinitis pigmentosa and chorioretinitis.