Natural accommodation in the growing chicken.

A new technique, Infrared Photoretinoscopy, has been employed for recording natural accommodation in the chicken. The illumination of the pupil by the fundus reflection of infrared light provided by high output light emitting diodes (I.R. LED's) was monitored on a video screen. The defocus of the eye could be calculated by evaluating the fraction of the pupil which was illuminated. It was found that: in the chick the full range of accommodation (about 17D) is present in the first day after hatching, accommodation acts completely independently in both eyes, the "near pupillary response" is weaker in younger chicks, the pupil constriction in response to light starts at higher luminance in the younger chicks the developmental decrease of the f/number is not sufficient to explain the change of the pupil reaction to light. Problems resulting from the use of drugs in order to measure the refractive state using normal retinoscopy are discussed.