Optical lens tinting and wavelength-specific filters
Optical lens tinting and wavelength-specific filters
Optical lens tinting is a technique used in the treatment of a variety of conditions that cause significant patient discomfort from photophobia. It was first developed in the late 1980’s with the first successful lens being dubbed the FL-41 lens designed to improve productivity in the workplace secondary by mitigating discomfort from fluorescent lighting. They are designed to block specific wavelengths of light that were observed to induce photophobia by dying the lens. More recently, optical notch filters have been developed that operate by the same principle; however, instead of tinting the original lens, a thin film is applied over the lens that provides a more specific wavelength blockade.
Mechanism of efficacy
Wavelength-specific blockade functions by reducing the amount of light that activates phototransduction in intrinsically photosensitive retinal ganglion cells (IPRGC). These cells are dubbed “intrinsically photosensitive” because they have been shown to transduce light signals even in the absence of traditional rod and cone photoreceptors. Stimulation of these cells has been linked to circadian rhythms, the pupillary light reflex, and nociceptive centers in the thalamus. IPRGCs contain a pigment called melanopsin that is bi-stable, isomerizing between its all-trans and 11-cis forms when exposed to light of 481nm and 587nm, respectively. Isomerization of this pigment is thought to be implicated in the IPRGC phototransduction pathway, so blockade of light with a wavelength around 481nm is theorized to reduce IPRGC phototransduction. This is clinically applicable in a patient with photophobia, because it may prevent activation of thalamic pain centers that would have normally been activated by the 481nm component of ambient light.
Photophobia is a prominent feature of many conditions, but wavelength-specific light filtering has not been studied in all of them. Prominent disorders that have been researched include migraine, post-concussion syndrome (PCS), benign essential blepharospasm (BEB), and disorders of cone photoreceptors. The filters have not been shown to help with efferent problems (e.g. convergence insufficiency or reading speed in PCS), but have shown a great deal of promise mitigating symptoms of photophobia which often affect patients’ quality of life. In migraine and BEB, wavelength blockade around 480nm has shown efficacy. It is important to block blue-green light. FPCS patients have reported improved comfort subjectively with a variety of lenses, but the trials have been small. Though also limited by sample size, patients with cone disorders have shown the most convincing improvement, and the treatment studied for them was using red contact lenses. The trials across all diseases have been limited by relatively small sample size, but a majority show objective improvement in patient symptoms, and they almost universally show a subjective improvement in symptoms.
Barriers to implementation
Barriers to implementation include low availability in optical shops and awareness of tinted lenses as a treatment option by physicians. Tinted lenses are available online, but they may be expensive, and this limits patients’ ability to trial the glasses before buying them.
Some commercially available lenses/glasses are labeled FL-41 and do not work as FL-41 protection. One must be careful and make sure the supplier is legit.
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