The refractory power of eye is normally 59 diopters. Two-thirds of this is contributed by
**Core Concept**
The refractive power of the eye refers to its ability to bend light and focus it on the retina. The eye's refractive power is primarily determined by the shape of the cornea and the lens, with the cornea responsible for approximately two-thirds of the eye's total refractive power.
**Why the Correct Answer is Right**
The cornea, being the outermost layer of the eye, is responsible for refracting light as it enters the eye. The cornea's refractive index is significantly higher than the surrounding air, allowing it to refract light and contribute to the eye's total refractive power. The cornea's curvature and refractive index work together to bend light rays, with the cornea accounting for approximately 2/3 of the eye's total refractive power. This is due to the cornea's significant contribution to the eye's total refractive power, with a value of approximately 40 diopters.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the lens, while also contributing to the eye's refractive power, is not responsible for two-thirds of the eye's total refractive power.
* **Option B:** This option is incorrect because the vitreous humor, although it does have some refractive power, is not responsible for two-thirds of the eye's total refractive power.
* **Option D:** This option is incorrect because the retina, being the innermost layer of the eye, is not responsible for refracting light or contributing to the eye's refractive power.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the cornea's refractive power is significantly influenced by its curvature and refractive index, which can be affected by various factors such as keratoconus or corneal injuries.
**Correct Answer: C. The cornea.**