Visual acuity tester

A spot of light e.g. from source 20 and aperture, plate 22 may be scanned across the eye by mirror 24 and is increased in intensity (by 56) until observed by the eye. The intensity at which this occurs is a measure of visual acuity. The subject operates a switch 66 when the spot is observed or the operator watches the subject's eye with television camera 58 to detect the commencement of tracking when switch 68 is operated. Before the acuity measurement an automatic measurement of refractive error may be made by pattern generator and detector 44 coupled to computer 46 and a cylindrical lens 26 and focussing lens 42 are adjusted for 20/20 vision. Target 30 is also adjusted to relax accommodation of the eye.