focus on low vision

Using Filters

Alex Yoho, ABOM

Diagnoses that benefit from the use of filtering lenses fall into several categories: photophobia and glare from lighting; diminished contrast; haze from light scatter; and problems adapting to varying light levels.

THE OPTIONS

Low vision practitioners are probably most familiar with The Corning CPF series lenses. The numbers contained within the names of these glass photochromic lenses—e.g., CPF 550, CPF 511—refer to the spectral cut-off of the particular filter.

Today, lens tint manufacturers offer filter dyes that can give similar properties to plastic lenses. Many fit-over sunglasses have filtering capabilities and comfort tints that can be beneficial by themselves or filters/tints that can be duplicated by your lab for ophthalmic eyewear.

RX RAINBOW

In addition to having a good basic tint selection, you should have many color/filters available for low vision diagnosis, including items for general population use for contrast enhancement or glare reduction. Whenever possible, have these made up in clip-on form so they can be realistically evaluated. In addition to regular cosmetic tints, offer:

■ APRICOT. Ranging in color from yellow to deep orange/red filters in this family are most often used to improve contrast by reducing glare primarily caused by blue light scatter. These address edge discrimination that seems to be improved making low vision patients more comfortable in awareness of their surroundings.
■ YELLOW Lenses with yellow filter/tints are the first option for opacities or distortions such as cataract or corneal irregularities that cause glare by scattering blue light.
For photophobics, darker yellow tones such as green may work better. A lighter option is the FL-41 filter tint developed for blepherospasm.
■ PLUM/MAUVE. These are useful in cases of photophobia, particularly in albinism.

THE PROCESS

Begin with the lightest color in the color group that you suspect will have the most benefit for the pathology being addressed. Try successively darker f ilters in the color group until a balance is achieved between light transmittance and reducing glare. EB