## Core Concept
Aniseikonia is a condition related to the difference in the perceived size and shape of images seen by each eye. This discrepancy can lead to difficulties in binocular vision and depth perception. The term is significant in ophthalmology and optometry, especially in the context of correcting vision problems.

## Why the Correct Answer is Right
The correct answer, **D. Difference in image size perceived by the two eyes**, accurately describes aniseikonia. This condition occurs when there is a significant difference in the magnification of images as seen by each eye. This can happen due to various reasons such as anisometropia (unequal refractive errors between the two eyes), cataract surgery with different lens powers in each eye, or the use of corrective lenses (glasses or contact lenses) that cause unequal magnification.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is not provided, but typically, an incorrect definition or unrelated term would be given. For the sake of explanation, let's assume it refers to "Same image size perceived by the two eyes," which would be the opposite of aniseikonia.
- **Option B:** Assuming this option refers to "Equal image size but different shapes," it does not accurately describe aniseikonia, which specifically deals with the difference in size, not shape.
- **Option C:** If this option suggests "No difference in image perception," it would also be incorrect as it contradicts the definition of aniseikonia.

## Clinical Pearl / High-Yield Fact
Aniseikonia can significantly affect a person's ability to perform tasks that require depth perception, such as driving or certain types of work. Clinically, it's essential to consider aniseikonia when prescribing corrective lenses or planning refractive surgeries to minimize its impact on the patient's vision and daily activities.

## Correct Answer: D. Difference in image size perceived by the two eyes