## **Core Concept**
The Hess test, also known as the Hess screen test or Lancaster-Hess test, is a clinical assessment tool used to evaluate the field of vision and detect any defects, particularly in patients with strabismus or suspected strabismus. It helps in determining the presence and extent of any heterotropia (strabismus) by assessing how a patient's eyes move in relation to a visual stimulus.

## **Why the Correct Answer is Right**
The Hess test involves the use of a tangent screen with a red and green background presented to each eye separately. The patient wears red-green glasses, allowing each eye to see a different background. The patient then maps out their field of vision by identifying where they see the point of a flashlight (or similar stimulus) as it moves across the screen. This test effectively assesses the field of vision for each eye and can reveal areas where there is a discrepancy in the visual field between the two eyes, indicative of strabismus. Therefore, the Hess test is specifically related to assessing strabismus.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically incorrect options might relate to other ophthalmological tests or assessments not directly related to strabismus or field of vision testing in the context of ocular motility.
- **Option B:** Similarly, without the content of Option B, it's assumed that any incorrect option would relate to a different clinical test or assessment not directly associated with the evaluation of strabismus through field of vision mapping.
- **Option C:** Again, without specifics, it's inferred that Option C would pertain to another ophthalmic or non-ophthalmic assessment not relevant to strabismus evaluation via the Hess test.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the Hess test is particularly useful in diagnosing and assessing the extent of strabismus, especially in cases where the deviation might be variable or where there are concerns about binocular vision. The test can help differentiate between concomitant and incomitant strabismus and guide treatment planning.

## **Correct Answer:** D. Strabismus.