Corneal apex in keratoconic patients

Eyes of 27 patients with keratoconus and 37 normal persons were examined with a photokeratoscope. The photokeratoscopic data were analyzed to obtain information about the corneal apex and a comparison between the two groups was performed. The study demonstrates a significant shift in the position of the corneal apex in relation to the visual axis from a superior-temporal position in the normal group to an inferior position without temporal-nasal preference in the keratoconic group. However, the magnitude of the apex displacement (lxa) was equal in the two groups both in the horizontal and vertical direction. The influence of xa on the stability of the central corneal curvature was established by the apex factor (AF). The magnitude of AF depends as well on xa as the corneal shape. In the keratoconic eyes the vertical AF is about 5 times the horizontal AF, whereas in normal eyes the AF is equal in the two meridians. Thus the increasing astigmatism so characteristic for the keratoconic eyes may be caused by unequal alteration in the shape of the horizontal and vertical meridians.