Corneal surface area: an index of anterior segment growth

Corneal surface area and perimeter were assessed as novel indices to monito r anterior segment growth, using chicks reared under different photoperiods . We obtained central and mid-peripheral corneal curvatures using photokera tometry. Anatomical tracings of the anterior corneal surface also were made from freeze-dried non-fixed preparations of the anterior segments of the s ame eyes. Using either photokeratometry or anatomical data, the profile of the anterior corneal surface was fit to a general equation for conical sect ions; corneal surface area was estimated from surfaces of revolution. Optic al techniques modeled the chick cornea as a circle or as an ellipse closely resembling a circle. The anatomical technique, in contrast, modeled the ch ick corneal profile as a hyperbola. Potential explanations of this discrepa ncy are discussed. Regardless of which model is evaluated, the corneal surf ace area and perimeter of two-week-old chicks are affected by the photoperi od of rearing. Corneal surface area in particular proved more sensitive tha n conventional measurements in identifying anterior segment effects of rear ing under different photoperiods. Analysis of corneal area may prove useful in evaluating the mechanisms governing anterior segment growth. (C) 2001 T he College of Optometrists. Published by Elsevier Science Ltd. All rights r eserved.