What feature is critical for assessing the peripheral fit of a lens?

The assessment of a lens's peripheral fit is crucial for ensuring optimal comfort and vision quality. The fluorescein pattern is particularly significant because it provides visual feedback on how well the lens conforms to the shape of the eye, specifically in the peripheral cornea. When fluorescein dye is applied, it fills the space between the lens and the cornea, highlighting areas of contact and revealing areas where the lens may be too tight (bearing down) or too loose (potentially moving excessively).

A well-defined pattern indicates that the lens is fitting correctly, while uneven distribution or excessive pooling could signal a poor fit that may lead to discomfort or vision distortions. The fluorescein pattern directly relates to the lens's interaction with the corneal surface, which is key in assessing the peripheral fit, making it an essential feature during fitting evaluations.

Other options like lens color, illumination, and lens flexure are less relevant in the context of fitting assessment. While illumination can enhance visibility during examination, it doesn't provide the specific feedback on the lens's relationship with the cornea that fluorescein does.