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: (A) ab, (B) bc, (C) abc, (D) bcd
Answer is C. 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.