Information AboutVisual Field |
| CATEGORIES ABOUT VISUAL FIELD | |
| vision | |
| ophthalmology | |
|
The term is often used in Optometry and Ophthalmology , where a Visual Field Test is used to determine whether the visual field is affected by diseases that cause local Scotoma or a more extensive Loss Of Vision . NORMAL LIMITS The normal human visual field extends to approximately 35 degrees nasally (toward the nose, or inward) in each eye, to 90 degrees temporally (away from the nose, or outwards), and approximately 50 degrees above and below the horizontal meridian. In the United Kingdom , the minimum field requirement for driving is 60 degrees either side of the vertical meridian, and 20 degrees above and below horizontal. The Macula corresponds to the central 13 degrees of the visual field; the Fovea to the central 3 degrees. MEASURING THE VISUAL FIELD The visual field is measured by Perimetry . This may be kinetic, where points of light are moved inwards until the observer sees them, or static, where points of light are flashed onto a white screen and the observer is asked to press a button if he or she sees it. The most common perimeter used is the automated Humphrey Field Analyzer. Patterns testing the central 24 degrees or 30 degrees of the visual field, are most commonly used. Most perimeters are also capable of testing the full field of vision. VISUAL FIELD LOSS Visual field loss may occur due to disease or disorders of the Eye , Optic Nerve , or Brain . Classically, there are four types of visual field defects:1
In humans, confrontational testing and other forms of Perimetry are used to detect and measure visual field loss. Different neurological difficulties cause characteristic forms of visual disturbances, including Hemianopsia s (shown below ''without'' Macular Sparing ), Quadrantanopsia , and others. REFERENCES EXTERNAL LINKS
|
|
|