Three-dimensional model for human anterior corneal surface.

The anterior corneal asphericity (Q) with the tangential radius is calculated, and a three-dimensional (3-D) anterior corneal model is constructed. Tangential power maps from Orbscan II are acquired for 66 young adult subjects. The Q-value of each semimeridian in the near-horizontal region is calculated with the tangential radius. Polynomial fitting is used to model the 360-semimeridional variation of Q-values, and to fit the Q-values in the near-vertical region. Furthermore, a customized 3-D anterior corneal model is constructed. The 360-semimeridional variation of Q-values is well fitted with a seventh-degree polynomial function for all subjects. The goodness of fit of the polynomial function was >0.9, and the median value was 0.94. The Q-value distribution of the anterior corneal surface showed bimodal variation. Additionally, the Q-values gradually become less negative from the horizontal to the vertical semimeridians in the four quadrants. The 3-D surface plot of the anterior corneal surface approximated a prolate ellipsoid. Using a method to calculate the Q-value with the tangential radius combined with polynomial fitting, we are able to obtain the Q-value of any semimeridian. Compared with general models, this method generates a complete shape of the anterior corneal surface using asphericity.