A technique for in vivo measurement of photoreceptor orientation in the chicken retina

The aim of the current study was to develop a method for simultaneously assessing central and peripheral photoreceptor alignment in vivo in animal models. The stimulus apparatus consisted of nine light-emitting diodes (LED) positioned 7.5 degrees apart around an arc. The stimulus was viewed through a pinhole imaged into the entrance pupil of the eye using a telecentric lens system. Photodiodes placed over an array of the VERIS imaging system stimulated the electroretinogram. Data were obtained by positioning the pinhole at 0.25-mm intervals across the pupil and recording (Volk Optical, Mentor, OH, USA) at each location. Orientation assessed in normal chickens demonstrates that photoreceptors orientate towards a locus near the centre of the pupil and that there is a systematic change in peak location with eccentricity. This technique provides a valuable method for determining photoreceptor orientation properties in vivo and can be applied to animal models of pathology.