clinical maxwellian view system (redirected from Potential Acuity Meter)

maxwellian view system, clinical

Instrument designed to measure visual acuity by using a narrow beam or beams of light focused within the entrance pupil of the eye. The location of the beam or beams within the pupil can be controlled by the clinician. Such an instrument is valuable to assess acuity when part of the pupil is obstructed by a cataract or other opacity as the beam or beams of light can be directed to enter the eye through an area of the pupil where there is no opacity, thus providing an estimate of the visual acuity unaffected by optical image degradation. The results can contribute to the decision as to whether removal of a cataract will be beneficial. There are several types of these instruments. The Potential Acuity Meter (PAM) focuses a single beam of light in the pupil and a letter chart onto the retina. Others focus two beams of light in the pupil and a grating which can be produced on the retina by interference (if the two sources are coherent). This method is called laser interferometry. Examples of these are the Lotmar Visometer and the IRAS Randwal Interferometer, which are referred to as clinical interferometers. They tend to penetrate dense cataracts better than the PAM. See coherent sources; blue field entoptoscope; hyperacuity; interferometer.