American Board of Ophthalmology (ABO) Practice Exam

Where should trifocal lenses be positioned?

1. At the top edge of the pupil

2. At the center of the pupil

3. At the lower edge of the pupil

4. 1 cm above the pupil

The correct answer is: At the lower edge of the pupil

Trifocal lenses are designed to provide clear vision at three distinct focal lengths: for near, intermediate, and distance vision. The positioning of trifocal lenses is crucial for optimizing visual performance and ensuring that the wearer can effectively use all prescribed zones of the lens. When trifocal lenses are positioned at the lower edge of the pupil, this placement allows for the proper alignment of the reading segment with the user's natural gaze when looking down. The lower segment of the trifocal lens is intended for near vision tasks, which typically require the user to look downward. This positioning ensures that the wearer can see clearly for close-up activities, such as reading or working on a computer, without having to tilt their head or adjust their gaze excessively. While other positions might influence the functionality of the lenses, placing them at the lower edge of the pupil optimizes the use of the near segment while maintaining accessibility to the intermediate and distance zones as the user shifts gaze. This consideration is critical in ensuring that patients receive the maximum benefit from their trifocal lenses across all intended distances.