Night blindness mainly occurs due to interference with the functions of rods owing to deficiency of visual purple. All of the following are causes of night blindness, EXCEPT:
**Core Concept**
Night blindness is a condition characterized by difficulty seeing in low light environments. It is primarily associated with the function of rod cells in the retina, which are responsible for peripheral and night vision. Rods contain a photopigment called rhodopsin, also known as visual purple, which is sensitive to low light levels.
**Why the Correct Answer is Right**
Night blindness can be caused by various factors that affect the function or structure of rod cells, including nutritional deficiencies, genetic disorders, and systemic diseases. The correct answer is the option that is least associated with night blindness. The other options are all potential causes of night blindness, whereas the correct answer is a condition that does not primarily affect rod cell function.
**Why Each Wrong Option is Incorrect**
**Option A:** Vitamin A deficiency is a well-known cause of night blindness, as it leads to a decrease in rhodopsin production and function.
**Option B:** Retinitis pigmentosa is a genetic disorder that affects the structure and function of rod cells, leading to night blindness.
**Option C:** Diabetes can cause night blindness due to the damage it inflicts on the blood vessels in the retina, including those supplying the rod cells.
**Clinical Pearl / High-Yield Fact**
It is essential to note that night blindness can also be a symptom of other systemic conditions, such as celiac disease, anemia, and certain medications.
**Correct Answer:** D.