The effects of photoperiod and lid suture on eye growth in chickens

Three models of postnatal eye enlargement in leghorn chicks (surgical fusion of the eyelids, MES; exposure to continuous light, 24L; prolonged darkness, OL) were characterized on a morphologic and temporal basis, and a relationship between photoperiod and eye growth was described. While pronounced enlargement of the eye was evident in the OL and MES groups after 6 wk, a 15-wk experimental period was necessary to produce significant (P less than 0.05) eye enlargement under 24L. This enlargement was unaffected by pinealectomy and was characterized by increased equatorial diameter and decreased axial length. The macrophthalmos resulting from both MES and OL was characterized by increases in absolute and relative eye weights, axial length, and equatorial diameter. The MES eyes, however, showed a pronounced bulging of the cornea and increased anterior chamber depth and equatorial diameter, while those from the OL group had a flattened cornea and decreased anterior chamber depth. Finally, a relationship between photoperiod and eye growth was established and was best described by an inverse, continuous semilogarithmic function.