An instrument and method for characterizing eye-related optical systems, including the live human eye involves scanning an illuminating light beam from a light source and light detector unit from element to element of a beam deflector array of elements arranged laterally across the optical axis of eye. At each successive element the illuminating beam is deflected to form an interrogating beam that is directed into the eye at a peripheral angle that depends upon the lateral location of the deflector element. A return beam is reflected or back-scattered from the cornea and returned via the same deflector element to the light source and detector unit. This allows the interrogating beams to be scanned sufficiently rapidly into the eye to greatly reduce the variation of eye fixation and gaze that accompany other methods of measuring peripheral refraction or aberration of a natural eye. In addition to or instead of scanning the illuminating beam over each element of the array, all or multiple elements of the array can be illuminated simultaneously and the multiple interrogating rays thus generated can be gated by the use of an LCD aperture plate. Alternatively, an LCD aperture plate can be interposed between a wide illuminating beam and operated to selectively illuminate the beam deflector.