PHOTOPERIOD, EARLY POSTNATAL EYE GROWTH, AND VISUAL DEPRIVATION

(1) We studied the influence of photoperiod and unilateral lid suture on post-natal ocular growth in two types of White Leghorn chicks previ ously reported to respond differently to visual deprivation, Truslow a nd Cornell K chicks. We analyzed the chicks after 2 weeks of rearing, a time period commonly used in neuropharmacological studies of eye gro wth but much shorter than in most prior studies of photoperiod effects on the chick eye. (2) Altering the photoperiod length significantly i nfluenced the refraction and growth of both open and sutured eyes even at this early time, with differences between the two types of chicks. (3) The most prominent effect on the open eyes was the development of hyperopia with rearing under constant light, a response especially pr ominent in the Cornell K chicks. In the open eyes under this condition , the anterior chamber shallowed and the vitreous chamber elongated in the axial dimension only, reciprocal changes that resulted in no net alteration of axial length at 2 weeks. A high variability in refractio n of open eyes reared with constant illumination suggests the need for a dark period in the regulation of eye growth. (4) Compared to contra lateral open eyes, the lid-sutured eyes of both types of chicks develo ped longer total axial lengths and enlarged vitreous chambers in both axial and equatorial dimensions under each photoperiod. The effects on anterior chamber depth and refraction were complex and differed betwe en the two types of chicks. (5) The responses in open eyes support the notion that growth of the vitrious chamber of the chick eye is differ entially regulated in the axial and equatorial dimensions, previously indicated by pharmacological studies. The responses in both open and s utured eyes indicate different control mechanisms for anterior chamber and vitreous cavity growth.