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.
Children's Hospital BostonFamous quotes containing the words dark, adaptation and/or threshold:
“The change from storm and winter to serene and mild weather, from dark and sluggish hours to bright and elastic ones, is a memorable crisis which all things proclaim. It is seemingly instantaneous at last.”
—Henry David Thoreau (1817–1862)
“The real security of Christianity is to be found in its benevolent morality, in its exquisite adaptation to the human heart, in the facility with which its scheme accommodates itself to the capacity of every human intellect, in the consolation which it bears to the house of mourning, in the light with which it brightens the great mystery of the grave.”
—Thomas Babington Macaulay (1800–1859)
“The poorest man may in his cottage bid defiance to all the forces of the Crown. It may be frail—its roof may shake—the wind may blow through it—the storm may enter—the rain may enter—but the King of England cannot enter!—all his forces dare not cross the threshold of the ruined tenement!”
—William Pitt, The Elder, Lord Chatham (1708–1778)