Which situation may require increasing prism in bifocal lenses?

Increasing prism in bifocal lenses is often required to compensate for changes in lens positioning, particularly when lowering the lens position. When bifocal lenses are positioned lower than intended, the patient's line of sight may not align properly with the optical centers of the lens segments, especially the near segment. This misalignment can lead to visual discomfort and can cause issues with reading or other close-up tasks, as the patient may need to tilt their head or adjust their posture to see clearly through the segment. By increasing the prism, it helps to realign the visual axis and ensures that the patient can comfortably engage in near tasks without straining their eyes or neck.

The other circumstances do not typically necessitate an increase in prism. For example, while a tight fit can affect comfort and vision, it is not directly related to prism adjustments. Adjusting for pupil dilation typically involves considerations for the overall fit and lens power but does not generally require changes in prism. Changing lens material involves factors such as weight and optical clarity but again does not usually necessitate a change in prism unless the alteration significantly impacts fitting characteristics.