**Distichiasis Core Concept**
Distichiasis is a rare congenital or acquired condition characterized by the presence of a row of cilia (eyelashes) in addition to the normal row, often due to the abnormal growth of meibomian glands. This condition can lead to mechanical irritation of the cornea and conjunctiva, causing discomfort, tearing, and vision problems.

**Why the Correct Answer is Right**
In distichiasis, the abnormal eyelashes can rub against the eyeball, causing damage to the conjunctiva and cornea. This can lead to chronic inflammation, scarring, and vision impairment. The condition can be treated with electrolysis or surgery to remove the abnormal eyelashes.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because distichiasis can indeed cause mechanical irritation of the cornea and conjunctiva. The abnormal eyelashes can lead to chronic inflammation and scarring.
**Option B:** This option is incorrect because distichiasis can cause tearing and discomfort due to the mechanical irritation of the cornea and conjunctiva. The abnormal eyelashes can lead to chronic inflammation and scarring.
**Option C:** This option is incorrect because distichiasis can cause vision problems due to chronic inflammation and scarring of the cornea and conjunctiva.

**Clinical Pearl / High-Yield Fact**
In distichiasis, the abnormal eyelashes can be treated with electrolysis or surgery to remove the affected area. This can help alleviate symptoms and prevent further damage to the cornea and conjunctiva.

**Correct Answer: D. This option is incorrect because distichiasis is not typically characterized by a row of cilia in the lower eyelid.**