Dark adaptation threshold


Dark adaptation threshold

Dark Adaptation Threshold (DAT) is a vision test that measures the adjustment of the eye occurring under low levels of illumination. When light enters the eye, it ultimately reaches the rods and cones, which are two types of cells in the retina. Rods handle vision in low light conditions and cones handle color vision and detail. The rods and cones each react differently during the DAT test, and are measured on a graph. The test determines the threshold, or minimum light intensity required to produce a visual sensation in the child's eye. In order to perform this test, the child is asked to sit in the dark for a half hour. This allows the eyes to be most sensitive for the test. Once the eyes have fully adapted, the child stands in front of a black projection screen. Dim spots of light are projected onto the screen, one at a time, on either the right or the left side. The spots get dimmer as the test goes on. The child is asked to point to the spots until he or she can no longer distinguish them. In order to keep the child's attention on the screen, sometimes the doctor will wave a brighter light on the screen to hold the child's interest when the test becomes harder to see. When an infant is being tested, an observer with a night vision camera records the head and eye movements of the child as they look at the spots. Once the patient can no longer see the spots, the dark adapted threshold is determined. The DAT test lasts for about 10 to 15 minutes.

References

  1. DAT Testing Video

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Dark Shadows — For the upcoming film based on the soap opera, see Dark Shadows (film). Dark Shadows Title card Format Soap opera Created by …   Wikipedia

  • climatic adaptation — In physical anthropology, the genetic adaptation of human beings to different environmental conditions, such as extreme cold, humid heat, desert habitat, and high altitudes. Extreme cold favours short, round bodies with short arms and legs, flat… …   Universalium

  • List of The Dark Tower characters — The Dark Tower is a series of seven novels written by American author Stephen King, which incorporate multiple genres including fantasy, science fantasy, horror and western. Below are The Dark Tower characters that come into play as the series… …   Wikipedia

  • eye, human — ▪ anatomy Introduction  specialized sense organ capable of receiving visual images, which are then carried to the brain. Anatomy of the visual apparatus Structures auxiliary to the eye The orbit       The eye is protected from mechanical injury… …   Universalium

  • adaptometer — A device for determining the course of retinal dark adaptation and for measuring the minimum light threshold. * * * ad·ap·tom·e·ter .ad .ap täm ət ər n a device for determining the efficiency of dark adaptation in the human eye ad·ap·tom·e·try… …   Medical dictionary

  • environment — environmental, adj. environmentally, adv. /en vuy reuhn meuhnt, vuy euhrn /, n. 1. the aggregate of surrounding things, conditions, or influences; surroundings; milieu. 2. Ecol. the air, water, minerals, organisms, and all other external factors… …   Universalium

  • Germany — /jerr meuh nee/, n. a republic in central Europe: after World War II divided into four zones, British, French, U.S., and Soviet, and in 1949 into East Germany and West Germany; East and West Germany were reunited in 1990. 84,068,216; 137,852 sq.… …   Universalium

  • education — /ej oo kay sheuhn/, n. 1. the act or process of imparting or acquiring general knowledge, developing the powers of reasoning and judgment, and generally of preparing oneself or others intellectually for mature life. 2. the act or process of… …   Universalium

  • technology, history of — Introduction       the development over time of systematic techniques for making and doing things. The term technology, a combination of the Greek technē, “art, craft,” with logos, “word, speech,” meant in Greece a discourse on the arts, both… …   Universalium

  • arts, East Asian — Introduction       music and visual and performing arts of China, Korea, and Japan. The literatures of these countries are covered in the articles Chinese literature, Korean literature, and Japanese literature.       Some studies of East Asia… …   Universalium