tangent screen

screen [skrēn]

1. a framework or agent used as a shield or protector; called also protectant and protective.

2. to separate well individuals in a population from those who have an undiagnosed disease, defect, or other pathologic condition or who are at high risk by means of tests, examinations, or other procedures. See also screening.

Bjerrum screen tangent screen.

fluoroscopic screen a phosphorescent screen that shows the movement and relationship of organs and structures in fluoroscopy.

intensifying screen a fluorescent screen used in conjunction with x-ray film to enhance the effect of the radiation and reduce dosage to the patient. The screen must be matched to the emissivity range; the emissivity of phosphorus is similar to that of the human eye, so that phosphors absorb x-ray energy and convert it to visible light.

tangent screen a large square of black cloth with a central mark for fixation; used with a campimeter in mapping the field of vision.

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screen, tangent 

A large plane surface for detecting and plotting the central visual field (about 50º in diameter) by moving the position of a stimulus (e.g. a white 1 mm pinhead). It consists of dull black cloth or other material perpendicular to the line of sight and placed usually 1 m away from the subject (2 m gives more accuracy). In the centre of the screen is a white spot that provides a fixation point and a series of radial and circumferential lines are sewn or drawn to facilitate the localization of the stimulus. Syn. Bjerrum's screen. See campimeter; perimeter.