When evaluating fluorescein patterns, a special filter must be used with?

Using a special filter is essential when evaluating fluorescein patterns, particularly with polymers that have a UV blocker. This is because standard white light can obscure the fluorescence of the dye, leading to inaccurate assessments. The UV block polymers found in many lenses can affect how fluorescein is visualized. When a special UV filter is applied, it enhances the visibility of the fluorescein, allowing for a clearer evaluation of the tear film and the fitting characteristics of the lens on the eye.

This technique is crucial in contact lens fitting to assess areas of pooling, impingement, or edge lift that may not be apparent under regular lighting conditions. In other contexts such as evaluating soft lens materials, gas permeable lenses, or colored lenses, the unique properties of the materials combined with the fluorescence might not need the same filtration, making the usage of a special filter primarily relevant for those polymers that contain a UV blocker.