In an aphakic eye posterior focal point from the back of cornea is about:
**Core Concept**
The aphakic eye is a condition where the lens of the eye is absent or removed, requiring the calculation of the posterior focal point to correct vision. The posterior focal point is a critical concept in ophthalmology, especially in aphakic patients, as it determines the power of the intraocular lens (IOL) needed for proper vision correction.
**Why the Correct Answer is Right**
In an aphakic eye, the posterior focal point is calculated based on the power of the cornea. The cornea has a fixed power, and the posterior focal point is the point where light is focused after passing through the cornea. The power of the cornea is approximately 48 diopters (D), which is a critical value in calculating the posterior focal point. The correct answer is the one that corresponds to the posterior focal point calculated using the power of the cornea.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the power of the cornea, which is a critical factor in calculating the posterior focal point.
**Option B:** This option is incorrect because it uses an incorrect value for the power of the cornea, which would result in an incorrect posterior focal point.
**Option C:** This option is incorrect because it is the anterior focal point, not the posterior focal point, which is the point where light is focused before passing through the cornea.
**Clinical Pearl / High-Yield Fact**
In aphakic eyes, the power of the cornea is a critical factor in calculating the posterior focal point, and a mistake in this calculation can lead to incorrect IOL power and poor vision correction.
**Correct Answer: C. 25 cm**