Corneal surface area: an index of anterior segment growth

Corneal surface area and perimeter were assessed as novel indices to monitor anterior segment growth, using chicks reared under different photoperiods. We obtained central and mid-peripheral corneal curvatures using photokeratometry. Anatomical tracings of the anterior corneal surface also were made from freeze-dried non-fixed preparations of the anterior segments of the same eyes. Using either photokeratometry or anatomical data, the profile of the anterior corneal surface was fit to a general equation for conical sections; corneal surface area was estimated from surfaces of revolution. Optical techniques modeled the chick cornea as a circle or as an ellipse closely resembling a circle. The anatomical technique, in contrast, modeled the chick corneal profile as a hyperbola. Potential explanations of this discrepancy are discussed. Regardless of which model is evaluated, the corneal surface area and perimeter of two-week-old chicks are affected by the photoperiod of rearing. Corneal surface area in particular proved more sensitive than conventional measurements in identifying anterior segment effects of rearing under different photoperiods. Analysis of corneal area may prove useful in evaluating the mechanisms governing anterior segment growth.