Fig. 1. Diagrammatic cross-section of streak retinoscope. Light from the filament passes through the lens to the mirror, where it is reflected toward the patient. The examiner views through the aperture behind the mirror. The arrows represent the two controllable functions. The curved arrow indicates that the bulb may be rotated. The straight arrow indicates that the vergence of the light rays may be altered by changing the filament to lens distance. The filament is shown at the focal length of the lens so that parallel light rays emerge. (Weinstock SM, Wirtschafter JD: A Decision-Oriented Manual of Retinoscopy. Springfield, IL: Charles C Thomas, 1976.)