screen designed to measure the central visual field. Light spot patterns testing the central 24 degrees or 30 degrees of the visual field, are most commonly used. Most perimeters are also capable of testing up to 80 or 90 or even 120 degrees. Another method is for the practitioner to hold up 1, 2 or 5 fingers in the four quadrants and center of a patient's visual field (with the other eye covered). This is also known as confrontational field testing. If the patient is able to report the number of fingers properly as compared with the visual field of the practitioner, the normal result is recorded as "full to finger counting" (often abbreviated FTFC). The blind spot can also be assessed via holding a small object between the practitioner and the patient. By comparing when the object disappears for the practitioner, a subject's blind spot can be identified. There are many variants of this type of exam (e.g., wiggling fingers at visual periphery in the cardinal axes). Visual field loss Visual field loss may occur due to many disease or disorders of the eye, optic nerve, or brain. For the eye, e.g., Glaucoma causes peripheral field defects. Macular degeneration and other diseases affecting the macula cause central field defects. Lesions of the visual pathway cause characteristic forms of visual disturbances, including homonymous hemianopsia, quadrantanopsia, and scotomata. The main classification of visual field defects is into Lesions to the eye's retina (heteronymous field defects in Glaucoma and AMD) Lesions of the optic nerve (heteronymous field defects) Lesions in the chiasm (e.g. Bitemporal hemianopia, loss of vision at the sides) Lesions after the chiasm (homonymous field defects like homonymous hemianopia, Quadrantanopia, homonymous scotomata) Other characterisations are: Altitudinal field defects, loss of vision above or below the horizontal meridian – associated with ocular abnormalities Central scotoma, loss of central vision Peripheral field loss including tunnel vision Generalized depression of the entire field of vision Visual field defects in glaucoma In glaucoma, visual field defects result from damage to the retinal nerve fiber layer. Field defects are seen mainly in primary open angle glaucoma. Because of the unique anatomy of the RNFL, many noticeable patterns are seen in the visual field. Most of the early glaucomatous changes are seen within the central visual field, mainly in Bjerrum's area, 10°-20° from fixation. Following are the common glaucomatous field defects: Generalized depression: Generalized depression is