How do I determine the side of latent strabismus using cover uncover test?

To determine the side of latent strabismus using the cover-uncover test, follow these steps:

Steps for the Cover-Uncover Test

1. Preparation: Ensure the room is well-lit so you can clearly see the patient's eyes. Sit about 30 cm away from the patient to observe their eye movements effectively.

2. Patient Instruction: Ask the patient to focus on a near object (about 33 cm away) or a distant object (at least 3 meters away). Use a fixation target like a letter or a light.

3. Covering the Eye: Place an opaque or translucent occluder over one of the patient's eyes for a few seconds. Observe the uncovered eye for any movement. If there is no movement in the uncovered eye, proceed to the next step.

4. Uncovering the Eye: Remove the occluder from the covered eye and observe its movement. If the covered eye deviates (moves inward or outward) and then returns to its original position when the occluder is removed, it indicates a latent deviation (phoria) in that eye35.

5. Repeating the Test: Repeat steps 3 and 4 on the other eye to determine if there is a latent deviation in that eye as well.

Interpreting Results

• Esophoria: If the covered eye moves outward when uncovered, it suggests esophoria.
• Exophoria: If the covered eye moves inward when uncovered, it suggests exophoria.
• Hyperphoria or Hypophoria: If the covered eye moves upward or downward when uncovered, it suggests hyperphoria or hypophoria, respectively34.

By observing the direction of eye movement when the occluder is removed, you can determine the type and side of latent strabismus.

Additional Considerations

• Alternate Cover Test: This test can provide additional information about the total deviation (tropia plus phoria) but is more dissociative and may not specifically identify the side of latent strabismus35.
• Prism Cover Test: This can be used to quantify the deviation but is not necessary for determining the side of latent strabismus13.