Tinted Contact Lenses for Wavelength-Specific Treatments
BY LORETTA B. SZCZOTKA-FLYNN, OD, PHD, MS, FAAO
Many of us have fit the occasional patient with tinted contact lenses for therapeutic reasons. Such indications include improvement of photophobia secondary to aniridia and fixed surgical pupils, iris colobomas, iris transillumination in ocular albinism, or amblyopia management with solid black or black underprint occluding lenses in the dominant eye. However, there are other indications for which the tinted lens wavelength transmittance is thought to make a difference in treating the disorder. These conditions include photogenic (light-induced) seizures in epilepsy and color deficiency.
Photosensitivity is detected on EEG recordings in 5 percent of epilepsy patients (Capovilla, 2006), and up to 75 percent of them report visually induced seizures in their daily life (Quirk, 1995). Additionally, even in the absence of seizure elicitation, photosensitivity can cause a subjective unpleasant sensation and can induce a state of anxiety in photosensitive epilepsy patients, who are aware of possible reflex seizures (Capovilla, 2006).
Pharmacologic management for photosensitive epilepsy is not always effective and is associated with well-recognized toxicities (Kepecs, 2004). Non-pharmacologic approaches have included the use of sunglasses of various types. The effectiveness of spectacle (and contact) lenses for managing photosensitivity depends on both the lens color and transmittance (Takahashi, 1976; Takahashi, 1992). Several studies in the epilepsy literature have shown that blue-tinted lenses may help reduce the photoparoxysymal (photoconvulsive) response and may assist epilepsy patients who have photosensitivity. A photoparoxysymal response denotes an abnormal electroencephalographic response to photic stimulation, or brief flashes of light, which may be accompanied by minor seizures. Blue lenses have been shown to suppress the photoparoxysmal response more effectively than do lenses of other colors with similar overall transmittances (Kepecs, 2004).
Figure 1. Example of blue hue considered for contact lens correction for photosensitive epilepsy patients. Lens supplied by Alden Optical.
Capovilla et al (2006) have shown that a particular blue spectacle lens (Z1 from Zeiss) with a peak wavelength transmittance of about 470 nanometers was highly effective in controlling the photoparoxysmal response in a large number of photosensitive epilepsy patients. Six hundred ten photosensitive epilepsy patients, predominantly children (65 percent), were consecutively recruited across 12 epilepsy centers in Italy. Patients underwent EEG testing during photostimulation with and without the use of these blue-tinted spectacle lenses that have an 80 percent luminance cut. The lenses made the photoparoxysmal response disappear in the vast majority (76 percent) of patients, whereas the photoparoxysmal response was reduced in an additional 18 percent of them. Therefore, the overwhelming majority benefited from blue-tinted spectacle lens use.
A case report in a 2-year-old child who had severe myoclonic epilepsy and self-induced photogenic seizures showed that a blue-tinted contact lens reduced photosensitivity and inhibited the effect (Takahashi 1995). The patient induced seizure-generating behaviors and myoclonic (shocklike contractions of muscles) jerks by flickering hand movements and forced eye closure. The effectiveness of the tinted lenses could be related to the reduction of light frequencies between ~600 and 700 nanometers, indicating that some self-induced seizures may have wavelength specificity. In other words, the quantity of light stimulating red cones is believed to regulate seizure induction in these cases. Others have also reported that light stimulating only one set of retinal cones, and avoiding antagonistic effects from cones of other spectral sensitivities, could evoke photosensitive responses (Binnie, 1984). In summary, in patients for whom seizures are induced by flickering light, reduction of photosensitivity in the range of the red cone spectra (~600nm to 760nm) can reduce seizures.
Tinted lenses on the other end of the visible light spectrum have been used to assist color-vision-deficient patients with color discrimination. The concept of assisting color perception in color-deficient individuals with tinted contact lenses is not new, as it was first proposed in 1837 (See-beck, 1837). One of the historically most widely used lenses was the X-Chrom lens (various manufacturers), a red-tinted (historically rigid) contact lens, typically worn in the nondominant eye (Zeltzer, 1971). The ChromaGen lens system (Marietta Vision) offers various hues and density, theoretically allowing tint selection to be individualized for each patient in one or both eyes (Harris, 1997). Lens tints are available in seven hues (magenta, pink, violet, yellow, aqua, orange, and green).
Dating back to 1974, studies have shown that in systems in which a red or magenta lens is fit on the nondominant eye, performance on pseudoisochromatic plate testing can almost instantly be improved (La Bissoniere, 1974; Ditmars and Keener, 1976; Welsh et al, 1979; full list available at www.clspectrum.com). Most recently, Swarbrick et al (2001) studied the ChromaGen system in 14 color-deficient patients, nine with deutan defects and five with protan defects, and all were fit with either a pink or magenta tint in the nondominant eye. The tinted lenses significantly reduced Ishihara error rates, particularly for deutan subjects, improved errors on the D-15 test, and patients reported enhanced subjective color perception. The researchers concluded that such tinted lenses can enhance subjective color experience and assist in certain color-related tasks, but caution that color vision deficiency has not returned to “normal” in these patients.
Although an improvement in test scores can be noted, previous authors have noted that the improved effect is an artifact of patients utilizing achromatic luminance cues from the normally isoluminant circles in each plate that arise due to the introduction of the filters (Swarbrick, 2001). Therefore, color vision has not been normalized, and, in fact, although some color-pairs can be more readily discriminated, patients may then begin to confuse other color-pairs (Swarbrick 2001, La Bissoniere, 1974; Schmidt, 1976; and others).
In Clinical Practice
There appears to be sufficient and consistent data in the literature to support the use of blue-tinted spectacle lenses in photosensitive epilepsy patients. These patients should be treated in conjunction with the managing neurologist. Although much of the limited literature is based on spectacle lens correction, contact lens correction with similar tints has also worked and may be a better option for some individuals. Many newly diagnosed epilepsy patients are young children, a population in which spectacles are not always tolerated. Additionally, spectacle lenses can be dislodged during seizures, and contact lenses are thought to be beneficial in this regard. Figure 1 displays an example of this type of blue-tinted lens available from various specialty contact lens manufacturers and often sold in multiple lens packs.
With regard to color vision deficiency, there is good evidence spanning many years that a red or magenta lens in the nondominant eye can improve performance on both subjective assessments and color vision test scores. Color-deficient patients are often aware of this potential benefit and may approach specialty lens fitters in this regard. However, caution such patients that color vision is not normalized with use of tinted lenses and thus this form of correction is not indicated as a treatment for color deficiency in occupations with color vision-related restrictions. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #205.
Dr. Szczotka-Flynn is a professor in the Departments of Ophthalmology & Visual Sciences and Epidemiology & Biostatistics at Case Western Reserve University and senior optometrist at University Hospitals Case Medical Center Eye Institute. She is also the Director of the Coordinating for the CPTS Study. She receives research funding from Alcon and Vistakon.