Decibel scale humphrey visual filed3/29/2024 Refractive correction must be made with a test lens. Each eye is tested separately while the opposite eye is covered with a patch. The individual must be able to maintain a constant gaze toward a fixed location for several minutes. Several basic conditions must be met for a successful map of the visual field to be produced by any method. For dim night lighting (scotopic) conditions, the mid periphery is the most sensitive region of the visual field. The average blind spot is 7.5° in diameter, vertically centered 1.5° below the horizontal meridian 5). Definitive location varies slightly on an individual basis. A physiologic scotoma (a blind spot) exists at 15° temporally where the optic nerve leaves the eye. At this location, no photoreceptors are present, creating a normal absolute scotoma 4). Nerve fibers pass through the sclera at the optic nerve head, typically 10-15º nasal to fixation. The field of vision is often depicted as a three dimensional hill, with the peak sensitivity to stimuli occurring at the point of fixation under photopic conditions, decreasing rapidly in the 10º around fixation, and then decreasing very gradually for locations further in the periphery 3). From the point of fixation, stimuli can typically be detected 60º superiorly, 70º inferiorly, 60º nasally, and 100 degrees temporally (laterally) 2), though the true extent of the visual field depends on several features of the stimulus (size, brightness, motion) as well as the background conditions. Under normal daylight (photopic) conditions, the smallest or least intense visible objects are only seen in the central region of the visual field. The normal eye can detect stimuli over a 120º range vertically and a nearly 160 degree range horizontally.
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