Vertical head translation impairs dynamic visual acuity during near viewing.

Area of Science:

• Vestibular neuroscience
• Oculomotor function
• Human physiology

Background:

• Dynamic visual acuity assesses the rotational vestibulo-ocular reflex (rVOR).
• The translational VOR (tVOR) stabilizes gaze during linear head motion, but human studies show incomplete gaze stabilization.
• Visual environment significantly affects eye velocity during translation.

Purpose of the Study:

• To measure visual acuity during vertical head translation.
• To investigate if a complex visual background enhances tVOR response and improves dynamic visual acuity.

Main Methods:

• 11 subjects underwent 2 Hz whole-body vertical translation.
• Tumbling-E optotypes were flashed on a screen 30 cm away.
• Subjects reported optotype orientation via joystick; acuity determined by 75% correct trials.

Main Results:

• Group dynamic acuity was 0.72 logMAR (static acuity was 0.0 logMAR).
• Enhancing the background with a stationary dot pattern improved dynamic acuity to 0.42 logMAR.
• Vertical head translation degraded vision more than head rotation.

Conclusions:

• Dynamic visual acuity during vertical translation is significantly impaired compared to static acuity.
• A complex visual background can improve dynamic visual acuity during vertical translation.
• Impaired vision during vertical translation may limit its clinical utility for assessing otolith function.