**Core Concept**
Acquired blue blindness refers to the loss of ability to see blue colors in the visual spectrum. This condition is often caused by changes in the crystalline lens of the eye, particularly increased sclerosis or hardening of the lens.

**Why the Correct Answer is Right**
The correct answer is "C. Increased sclerosis of the crystalline lens" because as the lens becomes more sclerotic, it becomes more difficult for blue light to pass through. This is due to the selective absorption of blue light by the lens, which is more pronounced in older individuals or those with age-related lens changes. The lens's increased density and opacity lead to a reduced transmission of blue light, resulting in the perceived loss of blue color vision.

**Why Each Wrong Option is Incorrect**
* **Option A:** Disease of optic nerve typically affects the transmission of visual information from the eye to the brain, but it does not directly affect color perception or the transmission of blue light through the lens.
* **Option B:** Disease of the macula affects central vision and fine detail, but it does not specifically affect color perception or the transmission of blue light through the lens.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that acquired blue blindness is often a symptom of age-related lens changes, which can also be associated with other visual symptoms such as presbyopia and decreased visual acuity.

**✓ Correct Answer: C. Increased sclerosis of the crystalline lens**