**Core Concept**
Keratoplasty, also known as corneal transplant, is a surgical procedure that involves replacing the diseased cornea with a healthy donor cornea. This procedure is used to restore vision and improve the quality of life for individuals with corneal diseases or injuries.

**Why the Correct Answer is Right**
The therapeutic indication of keratoplasty includes conditions such as corneal scarring, corneal ulcers, keratoconus, Fuchs endothelial dystrophy, and other corneal disorders that impair vision. The procedure involves removing the diseased cornea and replacing it with a donor cornea, which helps to restore the cornea's transparency and function. This allows light to pass through the cornea and focus on the retina, improving vision.

**Why Each Wrong Option is Incorrect**
**Option A:** Keratoplasty is not a treatment for refractive errors such as myopia or hyperopia.
**Option B:** While keratoplasty can improve vision in individuals with corneal diseases, it is not a treatment for cataracts.
**Option C:** Keratoplasty is not a procedure used to treat conditions affecting the retina or optic nerve.

**Clinical Pearl / High-Yield Fact**
Keratoplasty is a highly effective procedure for restoring vision in individuals with corneal diseases, with a success rate of up to 90% in some cases.

**Correct Answer: D. Corneal scarring, corneal ulcers, keratoconus, Fuchs endothelial dystrophy, and other corneal disorders that impair vision.**