On the Position of the Plane of Stationarity in Laser Refraction

In the laser technique for subjective refraction the coherent laser beam illuminates the diffusing surface of a slowly rotating drum. The patient sees a moving speckle pattern which can be rendered stationary by the use of appropriate correcting lenses. It is shown that the patient's retina is not then, in general, conjugate with the frontal plane passing through the nearest point on the drum surface, but rather with a “plane of stationarity” whose position is a function both of the drum radius and of the curvature and obliquity of the incident coherent illuminating wavefront. An expression is derived for the position of this plane, and representative practical configurations are discussed, particularly with regard to the employment of the laser technique in accommodation studies.