True about cornea –a) Power is 43 Db) Majority of refraction occur at air – tear interfacec) With the rule astigmatism is present because vertical meridian more steep than horizontal meridiand) Spherical structuree) Refractive index 1.334

It has already been explained in this chapter that maximum refraction occurs from the anterior surface of the cornea (at the air-tear interface) because the difference between refractive index of two medium is maximum at this site. The air has a refractive index of 1.00 and cornea has refractive index 1.376, the difference is 0.376 (maximum). The cornea is not completely circular: Anterior surface (most important surface) is elliptical, while the posterior surface is circular. The vertical meridian of the cornea is 0.05 D steeper than the horizontal meridian, resulting in astigmatism with the rule. Refractive power of the cornea is 43-44 D.