[A study on the space form of the Schematic cornea of the normal adult eye-ball].

OBJECTIVE: To detect the initial characters of the corneal shape that has been evaluated using a mathematical analysis. METHODS: Subjects were measured with Orbscan II corneal topography system. Anterior and posterior corneal radius of curvature and thickness of the points located 1.5 mm, 2.5 mm, 3.5 mm and 4.5 mm away from the corneal apex on certain meridians, including 0 degrees , 30 degrees , 60 degrees , 90 degrees , 120 degrees , 150 degrees , 180 degrees , 210 degrees , 240 degrees , 270 degrees , 300 degrees and 330 degrees meridians, were measured. The mathematical formula of space-form of the cornea as well as the shape factor (SF) were demonstrated. Distributions of corneal curvature between the two principal meridians were discussed. RESULTS: Mathematical model of anterior and posterior corneal surface were small ha, Cyrillic(2)/8.053(2) + y(2)/7.973(2) + (z-8.226)(2)/8.226(2) = 1, x2/6.836(2) + y2/6.745(2) + (z-8.080)(2)/7.527(2) = 1 respectively. The SF models of the steepest and flattest meridians on anterior corneal surface were e(2) = 1-(15.61z-y2)/z2 and e2 = 1-(15.61 z-x2)/z2 respectively; the same parameters in the posterior corneal surface were e(2) = 1-[12.254 (z-0.553)-y2]/(z-0.553)(2) and e(2) = 1-[12.254 (z-0.553)-x2]/(z-0.553)(2) respectively. The curvature of oblique meridian was described with the formula F' = F(a) + (F(b)-F(a)).Sin(2)alpha. CONCLUSIONS: Anterior and posterior corneal surfaces are both toric similar to ellipsoidal. The distributions of corneal curvature between the two principal meridians have something to do with the law of Sine.