American Board of Ophthalmology (ABO) Practice Exam

What does excessive base-down prism OU typically result in for the wearer?

1. Blurred vision

2. Visual comfort

3. Feeling of balance

4. Feeling of descending

The correct answer is: Feeling of descending

Excessive base-down prism in both eyes can lead to a unique perceptual experience for the wearer. The addition of base-down prism causes the visual axis to shift downward, which can create a sensation of descending or feeling as though one's gaze is directed downward more than usual. This can disrupt the wearer's spatial awareness and cause the perception of a downward slope or a feeling of being at a lower elevation than reality. Visual mechanisms are intricately linked to how we perceive our environment, and excessive base-down prism can significantly alter that perception. The brain often compensates for the misalignment produced by the prism, but when the prism is too strong, this compensation can lead to disorientation and a feeling of descending. While blurred vision can occur if the prism is improperly prescribed or if the individual is not adapted to using prisms, excessive base-down prism specifically is more associated with the altered perception of space. Similarly, whereas visual comfort and feelings of balance are important aspects of visual function, they do not accurately describe the effects of wearing excessive base-down prism where the predominant sensation is that of being pulled downwards or descending.