The phi phenomenon describes the patient's perception of movement in what relation to the direction of deviation when the eye is uncovered?

The phi phenomenon describes the patient's perception of movement in what relation to the direction of deviation when the eye is uncovered?

• A. Opposite direction
• B. Same direction
• C. No movement
• D. Irregular movement

Answer: (A)

The phi phenomenon is the perceptual illusion that occurs during uncovering in the assessment of latent strabismus. When the eye that has been preventing fixation is suddenly uncovered, the patient often reports that the eye appears to move in the opposite direction to its actual deviation. This happens because the brain interprets the abrupt change in the retinal image during re-fixation as motion opposite to the direction the eye must move to align with the target. So, if the eye tends to deviate inward, uncovering it is perceived as outward movement. This opposite-direction perception is the hallmark of the phi phenomenon, rather than movement in the same direction, no movement, or irregular movement.

The phi phenomenon is the perceptual illusion that occurs during uncovering in the assessment of latent strabismus. When the eye that has been preventing fixation is suddenly uncovered, the patient often reports that the eye appears to move in the opposite direction to its actual deviation. This happens because the brain interprets the abrupt change in the retinal image during re-fixation as motion opposite to the direction the eye must move to align with the target. So, if the eye tends to deviate inward, uncovering it is perceived as outward movement. This opposite-direction perception is the hallmark of the phi phenomenon, rather than movement in the same direction, no movement, or irregular movement.