Light controls scleral precursor synthesis.
Both axial clongation and scleral precursor synthesis are increased during form deprivation myopia (FDM). Since axial clongation is greater during the day than at night during normal development, it seemed likely that the rate of scleral precursor synthesis would be high in the day and low at night. Instead we found that the rate of scleral precursor synthesis is greater in the middle of the night than at the middle of the day. The rise and fall do not begin until about 4 h after lights off or lights on, respectively. These variations in precursor synthesis are light-driven, not circadian.