Distinctive Mechanisms Regulating Corneal and Scleral Growth

Summary

To learn if the cornea adjusts passively to vitreous cavity expansion or if its growth is subject to an independent regulatory mechanism, chicks were raised under photoperiods with 12 or 24 hours of light. As previously described, continuous light rearing caused vitreous cavity enlargement, anterior chamber shallowing and corneal flattening compared to the other photoperiods. We previously found that, when assessed by optical or anatomical methods, the chick corneal surface area at 2 weeks of age was larger following rearing under a 12 hour light:dark photoperiod than under continuous light. With a spherical model for the chick corneal shape, optical methods suggest that corneal growth slows rather than arrests under continuous light, when vitreous cavity expansion is greatest. The photoperiod-related dissociation of vitreous cavity and corneal growth indicates that scleral and corneal expansion can be differentially regulated. Because of photoperiod dependency, neural mechanisms likely modulate post-natal corneal expansion.