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
Correct Answer: abc
Description: 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.
Category:
Ophthalmology
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