## Core Concept
The WHO's "Vision - 2020: The Right to Sight" initiative aims to eliminate avoidable blindness by the year 2020. It focuses on major causes of blindness and visual impairment that are treatable or preventable, emphasizing a comprehensive approach to eye care.

## Why the Correct Answer is Right
The main conditions targeted under the "Vision 2020" initiative include cataract, glaucoma, diabetic retinopathy, age-related macular degeneration, and refractive errors, among others. These conditions are prioritized because they are major causes of blindness and visual impairment worldwide, and there are effective interventions available for their prevention or treatment.

## Why Each Wrong Option is Incorrect
- **Option A:** Cataract is a leading cause of blindness worldwide and a major public health problem, particularly in developing countries. Surgical removal of cataracts is a highly effective intervention, making it a priority under Vision 2020.
- **Option B:** Glaucoma is another significant cause of irreversible blindness. Early detection and treatment can prevent or delay progression to blindness, making it a priority.
- **Option D:** Diabetic retinopathy is a complication of diabetes and a leading cause of blindness in working-aged populations. Early detection and laser treatment can prevent vision loss, so it's a priority.

## Why Option C is Incorrect (Correct Answer)
Assuming **Option C** represents a condition not listed among the main priorities (like cataract, glaucoma, diabetic retinopathy), without the specific details of what **Option C** entails, we can infer based on common knowledge of Vision 2020 priorities. Typically, conditions like onchocerciasis (river blindness), trachoma, and vitamin A deficiency are also major targets. If **Option C** does not represent one of these significant public health issues targeted by Vision 2020, it would be the correct answer as an "except."

## Clinical Pearl / High-Yield Fact
A key aspect of the Vision 2020 initiative is its focus on diseases that are treatable or preventable causes of blindness. A memorable point is that cataract, being a leading cause of blindness, especially in developing countries, has a very effective treatment - surgical removal, which is relatively inexpensive and can significantly restore vision.

## Correct Answer: C.