Peripheral vision
From Free net encyclopedia
Peripheral vision is a part of vision that occurs outside the very center of gaze. There is in actuality a very broad set of non-central points in the field of view that is included in the notion of peripheral vision. "Far peripheral" vision exists at the edges of the field of view, "mid-perpheral" vision exists in the middle of the field of view, and "near-peripheral", sometimes referred to as "paracentral" vision, exists adjacent to the center of gazeTemplate:Fact.
Peripheral vision is weak in humans, especially at distinguishing color and shape. This is because the density of receptor cells on the retina is greatest at the center and lowest at the edges (see visual system for an explanation of these concepts). In addition, there are two types of receptor cells, rod cells and cone cells; rod cells are unable to distinguish color and are predominant at the periphery, while cone cells are concentrated mostly in the center of the retina (the macula).
Peripheral vision is good at detecting motion (a feature of rod cells), however, and is relatively strong at night or in the dark, when the lack of color cues and lighting makes cone cells far less useful. This makes it useful for avoiding predators, who tend to hunt at night and may attack suddenly from ambush.
Peripheral vision loss may occur due to a number of ocular or neurological diseases or disorders. Glaucoma, stroke, branch retinal vein occlusion, branch retinal artery occlusion, ischemic optic neuropathy, and transient migraine are some of the more common causes, whereas retinitis pigmentosa, choroideremia, gyrate atrophy, pituitary tumors, optic disc drusen, brain tumors and aneurysms, and tilted optic discs are uncommon or rare [1].
Testing peripheral vision
- Close one eye. Extend your arms straight out to your sides
- Slowly swing your arms to your front, noting when you first see your hands.
- Do you see your hand opposite the closed eye hand 90 degrees from your nose?
- Do you see your hand on the same side as the closed eye 30 degrees from your nose?
- If yes, the test is normal.
- IXMUS Color Field Test Peripheral Vision Testing for Macular Degeneration and Optic Nerve Disease