An Overview of the Therapeutic Applications of Tinted Lenses Spectacles

Abstract

Although tinted glasses are part of the fashion and beauty world, these glasses have various therapeutic applications in normal people or people with eye and neurological problems in some cases have been ignored. Tinted spectacles produce their effects by reducing visible light transmission and filtering by removing a certain part of the spectrum and can reduce discomfort and annoyance and improve the quality of life. The therapeutic effects of these glasses are related to controlling photophobia, preventing glare and increasing contrast. These glasses are used in normal people as sunglasses, to improve sports activities, comfortable driving at night and to increase sleep quality. Colored glasses have also been widely used in people with low vision related to congenital and acquired retinal diseases and neurological diseases such as migraine, acquired brain injury, and photosensitive epilepsy. So far, numerous studies have been conducted on the beneficial and therapeutic effects of colored glasses, which sometimes report contradictory effects. In this article, we explore the therapeutic uses of colored glasses in more detail.

Introduction

Although the use of tinted optical glasses is common in the fashion world, they have many medical applications. The use of colored lenses began in the 1980s, designed to reduce eye strain and increase productivity in the workplace. In the following years, with the introduction of newer lenses, their use in the treatment of eye and neurological diseases gained more attention [1–3]. These lenses do their therapeutic effects through tinting or filtering. Glasses with tinted lenses reduce the transmission of visible light but do not filter out color. Later, optical filters were developed that work on the same principle, but instead of tinting the lens, a thin film is applied to the lens to block more specific wavelengths [4,5].

This article reviews the therapeutic applications of these lenses in various ocular and neurological diseases. This review was conducted using PubMed searches for the terms “tinted lenses,” “photosensitivity/photophobia with lens filters/tinted lens,” “therapeutic effects of optical filters/tinted lenses/sunglass,” and “ocular/neurological diseases AND optical filters/tinted lenses.” Articles from 1990 to the present were identified that addressed the therapeutic application of tinted lenses in ocular and neurological diseases. References of existing articles were also reviewed to search for other relevant articles. This study was conducted after approval by the Human Ethics Committee of Shahid Beheshti University of Medical Sciences (No. IR. SBMU.RETECH.REC.1398.255).

Mechanism of Efficacy

Colored lenses, by reducing the transmission of visible light and filters by eliminating a specific part of the spectrum, create their effects and can reduce discomfort and improve quality of life. In general, the therapeutic effects of these lenses are related to the control of photophobia, avoidance of glare and enhancement of contrast, which are expressed in three separate parts [6].

Photophobia is actually a neurological problem because the part of the eye that transmits photophobia to the brain is different from the part that transmits vision. Various factors, such as brightness of light, flashing of light, and wavelength of light can cause and exacerbate photophobia in someone who is already sensitive to light [7]. The brighter the light, the more likely it is to cause discomfort, pain, or aversion. People with photophobia have a lower tolerance for all light [8]. Stimuli with high visual contrast are another concern for people with photophobia. Striped patterns are also known to be triggers for people with photosensitive epilepsy and migraines [9]. Fluorescent lamps in particular have an invisible flicker that is inherent in the way they work. It may not be visible to the naked eye, but it is perceived by the brain and is a possible cause of headaches, seizures, migraine attacks, eye strain, and sensitivity to light [10,11].

Some wavelengths of light are more likely to activate the eye and brain, causing pain and eyestrain. Some patients with migraines and other headache disorders are triggered or exacerbated by exposure to certain wavelengths of blue light [12,13]. Stringham et al. [14] showed that photophobia discomforts increase with exposure to shorter wavelengths of light. However, photophobia acts as a biological protective function against potential retinal damage by short-wavelength light.

The human eye can see the visible part of the electromagnetic spectrum, including wavelengths about 380 to 780 nm [15]. The human eye have three known types of photoreceptor: rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs). Rods primarily mediate scotopic vision whereas cones primarily mediate photopic vision. The ipRGC are thought not to contribute to sight directly, but have a role in the entrainment of the circadian rhythm and the pupillary reflex [16]. Modulation of ipRGC phototransduction is thought to be influenced by melanopsin, a biphasic pigment found in ipRGCs that isomerizes between its all-trans and 11-cis forms upon exposure to 481 and 587 nm light, respectively [17].

Numerous lines of evidence in animal models and patients suggest that ipRGCs are involved in photophobia. The cells of the suprachiasmatic nucleus regulate circadian rhythms, and the cells of the Edinger-Westphal nucleus control the pupillary light reflex [17,18]. Zivcevska et al. [19] found that the characteristics of light-induced discomfort in healthy subjects are consistent with the characteristics of the light-emitting pathway of ipRGCs, which are inherently photosensitive. Marek et al. [20] showed that the wavelength-dependent light aversion was mainly mediated by melanopsin-containing cells, most likely ipRGCs. They observed that administration of a melanopsin antagonist reduced photosensitivity in mice. In the positron emission tomography findings of patients with photophobia due to essential blepharospasm, abnormal hyperactivity was observed in the thalamus [21].

Functional magnetic resonance imaging (fMRI) results showed that during photophobia, specific patterns in the trigeminal system were activated at the level of the trigeminal ganglion, caudate trigeminal nucleus, and ventral posteromedial thalamus. The anterior cingulate cortex, a brain structure associated with discomforts, was also activated during photophobia [22].

Despite the role of cells in causing photophobia, scientific evidence has suggested three pathways for the transmission of neural signals to the brain. In the first pathway, light stimulation of photoreceptors in the retina (whether rods, cones, or ipRGCs) activates trigeminal neurons in the brainstem, which in turn cause dilation of the eye vessels and activation of pain-sensing neurons in the blood vessels [23]. The second pathway is through direct communication between ipRGCs and thalamic nuclei that are involved in somatic sensation and pain [12]. The third pathway is through communication between ipRGC-like and/or ip-RGC-containing neurons in the iris and the trigeminal afferent branches [6,17].

Based on these findings, blue light–blocking lenses can minimize light transmission by ipRGCs and melanopsin isomerization, preventing activation of thalamic pain centers. So, these lenses that reduce exposure to light around 481 nm would decrease isomerization of melanopsin to its all-trans form and subsequent ipRGCs-mediated phototransduction to nociceptive centers in the posterior thalamus. Also, a possible placebo effect has been suggested in some studies [17,24,25].

Tinted lenses are known to influence contrast sensitivity by interfering with light transmission [26]. There are several studies on the effect of colored lenses on contrast, with some conflicting results. Lee et al. [27] reported improved contrast sensitivity with purple and blue lenses in normal subjects under glare conditions, but observed no change with a yellow lens. In other study, Green, brown, and blue filters did not cause significant changes in contrast sensitivity compared with a gray filter of equal luminance, although chromatic discrimination was disturbed. Yellow and orange filters improved achromatic contrast at certain spatial frequencies, but impaired chromatic discrimination [28]. Although yellow lenses reduced contrast sensitivity to a white on black grating, they provided significant improvements in low-to medium-spatial frequencies when measured using the white-on-blue grating. As a result, yellow lenses enhanced contrast when viewing bright objects against a blue-based background, such as the sky [29].

Singh et al. [30], indicated red and brown tints had the most negative impact on contrast sensitivity as compared to no tint, followed by green, gray, blue, and yellow. All tints cause a change in color perception. The most noticeable color vision degradation is shown in red and yellow hues, followed by brown, green, gray, and blue. Tints have an impact on contrast sensitivity and color perception, so we should educate those who wear tints on how to use them responsibly by understanding their effects. Shaik et al. [31] compared the effects of cosmetics tinted spectacle lenses on color vision and contrast sensitivity. Mild to severe degrees of blue, brown, and gray tinted lenses do not significantly alter color vision, but for selected levels of color transmission used, contrast sensitivity can be improved somewhat. Mahjoob et al. [32] investigated yellow filter on visual acuity and contrast sensitivity under glare condition for various ages. Results showed a significant reduction in contrast sensitivity under glare condition in all age groups, which improved significantly with the use of yellow filter especially in older subjects. Seelan et al. [33] studied visual performance of young adults by using tinted spectacles. Most subjects preferred yellow tint (50%) for visualizing low-contrast optotypes. Subjects with the yellow tint demonstrating the best visual reaction time.

Overall, previous research on the effects of different colors on contrast sensitivity is controversial, and no specific color can be definitively pointed to. Color filters appear to have a small to moderate effect on contrast sensitivity. Although most studies have focused on yellow, some have found that pink or blue are more effective. It is worth noting that many of these studies were conducted under artificial lighting conditions that are much lower than natural light intensity, which may confound the enhancing effects. Importantly, when prescribing medication, the individual’s working conditions and vision should be taken into account, and subjective assessments are likely to yield more effective results.

Shorter wavelengths of light scatter more than longer wavelengths, causing uncomfortable glare. Blue light causes more blur than other colors, which reduces blue light, improving the quality of the image on the retina. There is evidence that the use of filter lenses reduces glare [34].

Hammond [35] evaluated the effects of filtering short-wavelength light on visual performance under intense light conditions among pseudophakic patients. Photostress recovery time and glare disability thresholds were significantly improved when patients used blue light–filtering glasses. Blue light filtration increased tolerance to veiling white light and significantly lowered glare disability thresholds [36]. Yellow filters reduce the mean brightness of a set of colored samples significantly less with blue surrounds than with black, achromatic or yellow ones, in comparison with the naked eye and less than a yellow surround in comparison with a luminance-matched gray filter. The yellow filter is actually capable of significantly increasing the brightness with the blue surround both in comparison with the naked eye and with the neutral filter [37]. Ghorbanhosseini et al. [38] assessed the effect of colored filters for reducing glare symptoms in post-refractive surgery 70 patients. The results showed that yellow filters can be used to reduce glare and improve visual acuity, but red and green filters are poor choices for reducing glare in patients after refractive surgery.

In general, filtering shorter wavelengths tends to also spare visibility since blue light is off the peak of the photopic spectrum. So, blue light filtration reduce retinal exposure to the wavelengths that tend to be the most photophobic, and susceptible to atmospheric scatter while minimally absorbing the medium-to long-wave light that mediates object perception [38].

Therapeutic Uses of Colored Lense

Normal persons

1) Sunglasses

Glasses with tinted lenses are commonly used by normal people as sunglasses or comfort glasses. Tinted sunglasses are primarily designed for outdoor use to protect the eyes from the sun’s harmful rays. These glasses can improve vision based on individual needs and light conditions [39]. These lenses are specified by their color and luminous transmittance of the tint. Light tints with transmittances of about 75% to 85% are used for both cosmetic purposes and comfort. Moderately light tints with transmittances of about 50%, are often too dark for indoor wear and not dark enough to be effective sunglasses. Dark tints, which are commonly prescribed as sunglasses, have transmittances of approximately 20% [4,27]. The color of the lenses is chosen according to their function and the patients’ conditions. The choice of lens color should be appropriate for the lifestyle and activities of the individual. The correct colors improve the clarity of objects and increase the comfort and protection of the eyes. Lenses with pronounced coloring should not be recommended for persons with color deficiencies. Strongly tinted lenses, especially red or blue lenses, may affect traffic signal visibility, and long-term wear of these lenses may alter color perception for a considerable time after the lenses are removed [33].

Another point is about the protective effects of sunglasses. There is strong evidence that exposure to ultraviolet radiation (UVR) is associated with skin cancer, skin aging, and eye diseases such as pterygium, drop keratopathy, cataracts, eyelid malignancies, iris melanoma, and macular degeneration. The absorption of UVR by the eye depends on the tissues targeted, the age of the individual, and the wavelength received. Before the age of 8 to 10 years, 2% to 5% of the UVR received by the eyes can reach the retina, while this is only 1% to 2% by the age of 25 years. Sunglasses provide a protective barrier for the eyes, the effectiveness of which depends on the transmission of radiation from the sunglasses lenses, the geometry of the sunglasses, and the conditions of exposure. Sometimes sunglasses do not completely block UVR and must be combined with additional protective equipment [40–42].

2) Refractive errors

Contrast sensitivity is a vital aspect of vision that refers to the ability to distinguish objects with slight differences in brightness or color against a background. Contrast sensitivity is measured using patterns with varying levels of light and darkness. Positive contrast refers to black objects on a white background, while negative contrast refers to white objects on a black background. Reduced contrast sensitivity can affect daily activities, especially in low-light conditions or when faced with subtle differences in contrast, and can potentially affect driving, reading, and overall visual comfort. In refractive errors, particularly myopia, contrast sensitivity is reduced, especially in negative contrast, compared to people with normal vision. Individuals with myopia may have more difficulty distinguishing between bright and dark areas, especially when the difference is subtle. Also, individuals with hypermetropia may have difficulty distinguishing between objects of similar brightness, particularly in low light or at a distance [43].

Kalikivayi and Kalikivayi [34] assessed the influence of tinted spectacles over contrast sensitivity in both daylight and night conditions. In emmetropes, 20% yellow and pink tints did not reveal statistical significance for both positive and negative contrasts. In myopes, 20% pink tint did not reveal statistical significance for both positive and negative contrasts. In hyperopes, 20% yellow tint showed significance with positive contrast only. Both yellow and pink tints have better positive and negative contrast sensitivity up to 80% tint indicating their usefulness during night driving. In myopes and hyperopes, even 40% tint would be effective in enhancing the contrast for different backgrounds, especially in ocular conditions such as nighttime driving where contrast sensitivity is affected [34]. Palomo-Alvarez and Puell [44] assessed effects of yellow-tinted spectacle lenses on visual performance in children with reading difficulties. No effects of wearing yellow spectacles emerged on binocular vision, accommodation, oculomotor scanning, and reading speed in children with reading difficulties. These are the only articles available in this field, and more scientific studies are needed to draw better conclusions.

3) Sports activities

Athletes who participate in outdoor sports and recreational activities need protection from the sun’s rays. Tinted and polarized sunglasses are commonly worn by athletes during outdoor athletic activities. The benefits of wearing sunglasses include preventing foreign objects from entering the eyes, protecting them from ultraviolet rays [2]. Erickson [45] has collected some features and uses of colored glasses for athletes, which are summarized in Table 1. There are also other studies in this field, which are mentioned below.

Table 1.

Features and uses of colored glasses for athletes

Tint color	Feature	Condition	Sports
Gray	Equally absorb all wavelengths of the visible light spectrum	Athletes sensitive to color information and unable to perceive subtle changes in the natural environment	Golf, skiing, mountaineering
Yellow-brown	Reduced transmittance of short wavelength, decreased chromatic aberration mid-long wavelengths	In low-light conditions such as twilight, fog, cloudy	Shooting, snow sports, tennis, baseball, soccer, mountaineering
Green	Selective transmission of information in the green spectrum	Improved information from lines around grass and enhanced contrast of ball against the background	Golf, tennis, forest shooting
Red	Selective transmission of information at the end of visible light spectrum	In reddish clay environments against a background of brown soil, grass, blue sky	Trap shooting skating, skiers for “flat” light
Polarized	Reduced reflected glare off horizontal surfaces, especially water, snow, pavement, sand	Especially useful for wet surfaces	Fishing, water sports, driving, cycling
Photochromic	Change transmission characteristics against changes in light or ultraviolet	Recreational athletes in noncontact sports and in changing environmental conditions	Tennis, running, golf, cycling, fishing

Summary of features based on Erickson [45].

In a study by Mercatelli [46], polarized and nonpolarized sports sunglasses showed similar light transmission factors and were nearly equal in their ability to reduce outdoor light. Outdoor measurements showed that the light reflected by the road has a substantial polarized horizontal component. Polarized sunglasses block much of the light reflected by the road, resulting in a darker appearance of the road and reducing the glare of the scene in bright sunlight. The decrease in road luminance increases the contrast discrimination of other objects in the scene, which reflect sunlight in a nonpolarized way.

Kohmura et al. [47] studied the effect of colored lenses on visual attributes related to sports activities in students. There were no significant differences among lenses in dynamic visual acuity and depth perception. For hand-eye coordination, time was significantly shorter with colorless than dark gray lenses. Contrast sensitivity was significantly higher with colorless, light yellow, and light gray lenses than with dark yellow and dark gray lenses. In the evening condition, low-contrast visual acuity was significantly higher with colorless and light yellow lenses than with dark gray lenses, and in the evening plus glare condition, low-contrast visual acuity was significantly higher with colorless lenses than with the other colors except light yellow. Under early evening conditions and during sports activities, light yellow lenses do not appear to have an adverse effect on visual attributes.

Londe et al. [48] evaluated the acute effects of wearing colored-lens glasses on the intermittent endurance exercise test performance indicators and testosterone concentration. Their results suggest that wearing colored lenses does not influence high-intensity intermittent exercise performance and internal intensity indicators (rate of perceived exertion and heart rate responses) in amateur soccer players. However, wearing red-colored lenses during high-intensity intermittent exercise increases testosterone concentration after the session, and blue color seems to increase parasympathetic activity, improving heart rate recovery. Mehta et al. [49] assessed the effects of tinted lenses on stereopsis. The results showed these lenses decreased retinal illumination, and it was evident that there was a significant decline in stereopsis as the level of illumination decreased, regardless of tint condition.

Since there is a large amount of scattered blue light in adverse conditions such as cloudy skies, diffuse light, fog and snowfall, the use of blue light filters is recommended for athletes such as skiers. These filters have low transmission in the short wavelength range and a greater increase in transmission in the long wavelength range. Blue blockers that filter out blue light completely are relatively unsuitable for skiing because they limit the necessary perception of blue in peripheral vision. Blue attenuating filters are more suitable. These filters do not reduce the processing of information by the M and L cones without completely losing the blue information. On the other hand, the S cones can receive enough blue light to minimize color distortion [50,51].

In conclusion, colored lenses are used in athletes to reduce photophobia, improve contrast sensitivity, protect against glare or harmful radiation, and reduce glare. Informed selection of filters to use, also taking into account individual, environmental and climatic conditions, allows athletes to improve their visual comfort and sports experience. It should also be noted that these lenses do not reduce visual functions such as depth perception and color vision impairment.

4) Night driving

Driving at night can be challenging due to increased light distortions in the eyes caused by glare from vehicle headlights. Some people experience halos or increased sensitivity to bright lights in dark conditions. Headlight glare occurs when the main headlights fitted to a vehicle dazzle other road users, causing people to experience halos or increased sensitivity to bright lights in dark conditions. Some manufacturers of tinted glasses claim that yellow lenses increase road visibility at night and reduce glare from car headlights [52].

Hwang et al. [53] measured the association between yellow-lens glasses and pedestrian detection with and without headlight glare using a driving simulator equipped with a custom headlights simulator. The researchers found no significant differences in response times with different yellow lenses for different test conditions, and these lenses showed no advantage over clear lenses. Lacherez et al. [54] investigated the effects of yellow filters on objective improvement in visual tasks related to driving. In a low-contrast grating task, younger participants responded faster when using a yellow filter, but only when they were polarized. These filters helped improve the perception of peripheral objects. In another study, Izuka et al. [55] evaluated the effect of yellow lenses on reducing disability caused by ambient glare from headlights and improving contrast sensitivity. In the contrast sensitivity assessment, participants wore three types of lenses: clear, gray, and yellow. Results showed that wearing gray and yellow lenses at night significantly reduced contrast sensitivity, but wearing yellow lenses in glare conditions slightly improved contrast sensitivity. Despite this slight improvement, the use of yellow lenses at night is not advisable, as the overall disadvantages, such as reduced light input to the retina and potential reduced vision, surpass their benefits.

In conclusion, the benefits of using yellow lenses for night driving are questionable. In contrast to the research that shows the benefits of yellow lenses, other research has shown no sign of improvement.

5) Sleep quality

Blue wavelengths effectively regulate circadian rhythms, possibly through activation of blue-sensitive ipRGCs. Exposure to increasing amounts of artificial light during the night may contribute to the high prevalence of reported sleep dysfunction [56]. Blue light–blocking eyeglass lenses filter out short-wavelength visible light, preventing it from reaching the eyes and can create a form of physiological darkness. Some claims exist that they can improve visual performance with digital device use, provide retinal protection, and promote sleep quality. Some studies have shown that blue-blocking glasses are effective for inducing sleep and can be recommended as an effective intervention for patients with insomnia or delayed sleep phase [57–60].

Singh et al. [61] studied 17 randomized clinical trials, with 156 participants, and intervention follow-up periods from 1 day to 5 weeks. This systematic review indicated that blue light–filtering spectacle lenses did not reduce symptoms of eye strain with computer use, over a short-term follow-up period. Further, this review found no clinically meaningful difference in changes to critical flicker frequency with blue light–filtering lenses compared to non–blue-light–filtering lenses. Potential effects on sleep quality were also indeterminate, with included trials reporting mixed outcomes among heterogeneous study populations. There was no evidence from randomized clinical trial publications relating to the outcomes of contrast sensitivity, color discrimination, discomfort glare, macular health, serum melatonin levels, or overall patient visual satisfaction. Future high-quality randomized trials are required to define more clearly the effects of blue light–filtering lenses on visual performance, macular health and sleep, in adult populations.

6) Dyslexia

Dyslexia, a learning disorder that affects reading and writing, is often linked to visual stress. Some individuals with dyslexia report that words on a page seem to “swim” or blur, making reading a challenge. Tinted lenses are widely available for use by children and adults with dyslexia, and several studies have been conducted in this area. Some studies have shown a reduction in symptoms and discomfort with these lenses [62,63]. Systematic reviews to date indicated that there is still no reliable evidence to recommend tinted lenses for reducing reading difficulty or discomfort [64]. High-quality, low-bias research is needed to investigate their effectiveness in different forms of reading difficulty and discomfort for adults and children.

Ocular diseases

1) Chronic ocular pain

Chronic ocular pain can be defined as a painful sensation originating from the surface of the eye. Chronic ocular pain is a complex, multifactorial condition associated with dry eye disease, chronic inflammation, or neuropathies that can significantly interfere with a person’s daily activities and lead to a poor quality of life [65]. Since these patients suffer from photophobia, the therapeutic effects of colored lenses (FL-41) on photophobia and light-induced brain activity were investigated using fMRI in these patients. FL-41 lenses modulated photophobia symptoms in some individuals with chronic ocular pain. In conjunction, FL-41 lenses decreased activation in cortical areas involved in processing affective and sensory-discriminative dimensions of pain. Further research into these relationships will advance the ability to provide precision therapy for individuals with ocular pain [66].

2) Age-related macular degeneration

Age-related macular degeneration (AMD) is an acquired disease of the macula that causes significant impairment of central vision. Symptoms of these patients are decreased vision, central scotoma, and visual distortion. These patients have problems with their daily tasks due to reduced visual acuity and contrast sensitivity [67]. Previous studies indicated that intermediate and advanced AMD affects contrast sensitivity in humans under low-light levels [68]. In recent years, the use of blue light–filtering lenses has received attraction due to their potential to reduce the effects of light scattering and chromatic aberrations, as well as the possible protection they offer against the photo-oxidative effects [69]. The high proportion of blue light in daylight causes light scattering in the eye’s optical environment and creates a veil of stray light on the retina, resulting in reduced retinal image contrast [70]. Several studies have reported that tinted glasses and filters may improve visual function of AMD patients.

In a study by Wolffsohn et al. [71], red and gray lenses reduced contrast sensitivity and visual acuity in AMD patient whereas yellow and orange lenses increased contrast sensitivity. Bailie et al. [72] compared the visual effects of color filters with transmission-matched neutral density filters in dry AMD. Color filters had little effect on visual acuity and contrast sensitivity in patients with AMD but caused a small reduction in objective color vision, although this was not subjectively recorded by patients. Langagergaard et al. [73] evaluated the effect of LVI 527 lenses (Multilens) on contrast sensitivity in nonexudative AMD. These lenses are orange-yellow and absorb ultraviolet light as well as the blue end of the visible spectrum. LVI lenses improved contrast sensitivity in certain situations in patients with AMD. Jannat et al. [74] assessed the functional benefits of wearing colored filters (brown, amber, gray, orange, yellow) in dry AMD. Using colored filters significantly improved the visual acuity, with no contrast sensitivity improvement. Colombo et al. [75] evaluated efficacy of photochromic and selective blue light–filtering spectacle lenses on functional visual parameters in patients with central or peripheral scotoma due to retinal disease. With these filters, patients’ visual acuity and contrast sensitivity scores increased, and glare test scores were significantly reduced. The combination of a photochromic lens with a selective blue-violet light filter showed functional improvement in all patients. Caballe-Fontanet et al. [76] assessed selective cut optical filters (450, 511, and 527 nm) on quality of life in patients with AMD. Selective filters improved the quality of life of patients with AMD. The success rate in the fitting of filters is better for those with visual acuity lower than 0.25 and those with late or advanced AMD.

In conclusion, tinted lenses, especially blue light–blocking and yellow lenses, provide a small improvement in contrast sensitivity and glare reduction in patients with AMD especially in dry degeneration but do not affect patients’ visual acuity or color vision.

3) Low-vision diseases

Low-vision diseases include a wide range of diseases such as maculopathies, retinitis pigmentosa (RP), albinism, nystagmus, and aphakia following congenital cataracts. According to visual acuity, contrast sensitivity, glare sensitivity and subjective selection by the patients, tinted lenses and filters were prescribed. Colored filters are able to contribute substantially to rehabilitation of low-vision patients [77,78]. Several studies have reported that tinted glasses and filters may improve visual function of patients with low-vision diseases.

In a study by Cedrun-Sanchez et al. [79], short-wavelength light-absorbing filters increased visual discrimination capacity in low-light conditions in RP patients. In the study by Ahmad et al. [80], the contrast sensitivity of low-vision patients with a yellow filter was measured. In RP, contrast of 69% of patients was improved. All participants with pathological myopia showed significant results. There was no improvement in contrast sensitivity in participants with albinisim and Stargardt disease. In glaucoma, diabetic retinopathy and in macular scaring there was significant improvement. Abraham et al. [81] evaluated the effects of filters and illumination on contrast sensitivity in patients with cataract, pseudophakia, maculopathy, and glaucoma. Overall, filters were not beneficial for most groups at most illumination levels. Only in the maculopathy group was there a small improvement in contrast sensitivity at low illumination levels with the yellow filter, which could be considered in clinical practice and low-vision rehabilitation.

Photophobia is common in patients with albinism, especially those with hypopigmented fundus and poor visual acuity. Hansen et al. [82] studied 81 participants with ocular or oculocutaneous albinism. Participants were offered a wide range of filters and filter densities and could choose one for indoor or outdoor use. Participants were offered a wide range of filters with different densities and could choose one for indoor or outdoor use. Most participants preferred a relatively color neutral filter such as gray or brown and very few chose a filter with a distinctive color, such as orange. Sadeghpour et al. [83] evaluated the effect of color filters in patients with diabetic retinopathy. Optical filters (511 and 527 nm) improved contrast sensitivity, and the 527 nm filter slightly increased visual acuity.

Sodhi et al. [84] assessed the effect of yellow-amber no infrared glasses (blocking of ultraviolet and infrared light) on contrast sensitivity in subjects with retinal diseases. The results of this study showed that these filters had no effect on contrast sensitivity in people with macular degeneration, pathological myopia, hereditary maculopathy, and diabetic retinopathy. However, these filters may improve contrast sensitivity in people with good baseline visual acuity. Naidu et al. [85] assessed effects of tinted spectacle lenses on visual performance in patients with cataracts. All subjects, regardless of lens color, showed an increase in contrast threshold under glare conditions. While brown and yellow lens colors resulted in the least increase in contrast threshold, gray lens color resulted in the greatest increase in contrast threshold. Individuals with lenticular changes may benefit from brown or yellow spectacle lenses under glare conditions.

In general, the use of tinted lenses and filters has shown inconsistent results in people with low vision. Blue light–blocking, yellow lenses in RP patients provided minimal improvement of contrast sensitivity especially in low illumination. Patients with albinism showed no improvement of visual acuity and contrast sensitivity with tinted filters, but preferred neutral density filter lenses for photophobia. There were no improvements in diabetic retinopathy and maculopathies. In cataract patients, brown/yellow lenses showed improvement in glare symptoms. Many studies are flawed due to lack of control for investigator bias and the effects of placebo, learning, and fatigue. Little objective evidence is provided to support the reported improvements in visual function. Therefore, the use of tinted lenses in people with low vision remains controversial, and eye care professionals should continue to rely on anecdotal evidence to make decisions about lens prescription. Another consideration is the prescription of color filter lenses. Manufacturers recommend color filter lenses based on the initial diagnosis. However, many vision rehabilitation professionals evaluate a wider range of color filter lenses by trial and error before prescribing. This technique can be time-consuming. In one study, only half of patients chose a pair of color filter lenses that were on the manufacturer’s recommended list for their diagnosis. It seems that subjective trial and error regarding the types of color filter lenses is the best approach [78,86]. In another study, low-vision patients who complained of photophobia were permitted to select any one of five filters. The results showed that patients with certain types of pathology prefer to use specific filters to control the light reaching their eyes. Patients with albinism chose amber filters. Patients with glaucoma or diabetic retinopathy selected the same filter. Most patients with RP chose filters with 2% light transmission [87]. So, the vision rehabilitation professional should avoid prescribing lenses based solely on the manufacturer’s recommendations.

Neurological diseases

1) Migraine

Migraine is a one-sided headache that can cause severe, throbbing pain. It is often accompanied by nausea, vomiting, and extreme sensitivity to light and sound. The majority of migraine sufferers experience photophobia during an attack. Many patients report that light can trigger a migraine attack, and some are chronically sensitive to light [88]. Migraine sufferers experience sensitivity to bright lights and visual discomfort which are associated with hyperactivity of the visual cortex, known visual stress. Also, these patients have pattern glare (a sensitivity to striped or patterned visual stimuli) that can cause discomfort, visual distortions, and even pain. The use of color filters to treat visual stress and to prevent migraine has been investigated in several studies [89]. Patients wearing these filters have reported significant improvements in glare. The most likely mechanism for the effect of individually prescribed colored filters in migraine is the alleviation of cortical hyper-excitability and associated pattern glare [90]. In one study, 20 children with migraines were asked to wear either rose (FL-41) or blue-tinted glasses for 4 months. FL-41 is a rose-colored tint designed specifically to block blue-green light wavelengths that are commonly associated with migraines. After 1 month of wearing, all children showed an initial improvement in headache frequency. However, only children wearing rose-colored lenses maintained this improvement for 4 months. The improvement in headache frequency in these children was associated with a reduction in visually stimulated beta activity [91]. In another study, the use of “optimal” colored lenses in children with migraines and reading difficulties resulted in a reduction in the frequency of symptoms [92]. In a randomized study, Hoggan et al. [5] asked patients with chronic migraine to wear glasses that had either 480- or 620-nm light-blocking filter. The use of either 480- or 620-nm lenses resulted in clinically significant headache relief, with no significant difference between two lenses. Reduction of headache with 620-nm filter was associated with melanopsin, the photopigment in ipRGCs. This molecular property may explain the unexpected efficacy of the 620-nm filter. Some studies indicated that migraine patients appear to be sensitive to both red and blue wavelengths [5]. In another study, the researchers indicated wearing of green-tinted lenses lead to a decrease in the pupil constriction rate. In the heart rate variability analysis, the sympathetic nerve index was significantly higher in patients with migraine than in the control group with no lens and blue-tinted lenses, but there was no difference in the green-tinted lens group [93].

Because migraine is associated cortical hyperreactivity, Aldrich et al. [94] assessed the contrast detection thresholds of patients with migraine when wearing appropriate tinted lenses. In the evaluations, contrast detection in the visual field affected by halo was superior, which became more normal after using comfortable tinted lenses. These lenses were able to reduce cortical hyperreactivity in people with migraines and improve contrast perception. Individuals who experienced migraine with aura may be more susceptible to photophobia under typical lighting. Visual performance was improved using tinted lenses that provided light of the chosen comfortable color. The spectral power of that choice showed no evident relationship to melanopic energy [95].

Posternack et al. [25] developed optical tints based on the properties of ipRGCs excitation peak. These filters blocked wavelengths exacerbating migraine pain and transmitted wavelengths associated with comfort (green light). Participants were randomly assigned to wear either control lenses or these filters. These lenses were associated with clinically and statistically significant reductions in migraine at 2 and 4 hours.

In general, tinted lenses that reduce or filter out short wavelengths are effective because they reduce the activity of ipRGCs, leading to improved headache-associated pain and light sensitivity.

2) Cluster headaches

Cluster headaches cause severe, one-sided head pain. In some patients, bright lights trigger symptoms and cause photophobia [96]. In one case report, one patient with cluster headache wore spectacles tinted (yellow-green) when reading printed text. The spectacles absorbed short-wavelength light and were only worn during the prodrome period. The patient was free of cluster headaches for the 6 years after wearing the glasses, and the prodromes decreased in severity and frequency. The hypothalamus is highly active during cluster headaches and receives visual input from the ipRGCs [97]. In our searches, we found only this case report that reported a significant effect of tinted lenses on the patient’s headache. We believe that further research and scientific evidence are needed to draw conclusions.

3) Acquired brain injury

Acquired brain injury includes traumatic brain injuries (TBIs) following head trauma and accidents and nontraumatic injuries resulting from stroke, and neurological diseases such as multiple sclerosis. One of the most common complications of acquired brain injury is visual dysfunction. Many patients experience vision problems such as blurred vision, decreased contrast sensitivity, photophobia, difficulty focusing, eye movement disorders, deviations, and poor depth perception. These problems can initiate or exacerbate other symptoms such as dizziness, balance problems, and headaches. These patients have difficulty in daily activities reading, driving, and working [98,99]. Beneficiary effects of tinted lenses in acquired brain injury was indicated in several studies.

Clark et al. [100] studied 39 patients with TBI complained of photophobia. Using of colored glasses, photophobia were relieved in 85% of patients. Blue, green, red, and purple provided the most relief. In the study by Jackowski et al. [101], Corning Photochromic Filters (CPF) lenses improved letter contrast sensitivity and reading rate in patients with TBI. Fimreite et al. [102] prescribed color filters (gray, blue, and red) to patients with mild TBI who complained of light sensitivity and reading difficulties. Patients showed increased visual comfort and significant improvement in the reading-related parameters and visual evoked potential latency. Another study was conducted on military personnel and veterans who had photophobia and persistent headaches after TBI. Subjects reported significant improvements in light sensitivity, headache, and physical and cognitive symptoms after using personalized spectral filters. These filters were associated with symptom relief, increased subjective quality of life, and reduced use of objective medication for TBI-related headaches. These results support the proposed relationship between dysregulated light sensitivity and central pain regulation [103]. After brain injury, patients often suffer from photophobia, which contributes to decreased quality of life. A light-mitigation strategy can be easily used indoors as needed to optimize the relief. Many photophobic patients experience relief using colored sunglasses [100].

In conclusion, tinted lenses including gray, blue, CPF, and photochromic reduced photophobia in patients with brain injury.

4) Visually induced motion sickness

Visually induced motion sickness (VIMS) is a type of motion sickness that causes eye strain, headache, nausea, oculomotor strain, and disorientation. Visual stress such as watching dynamic visual content from various sources and using visual displays such as virtual reality cause VIMS in these patients [104]. Visual stress can often be reduced using spectral filters, provided the color is selected with precision to suit each individual [105]. Yadav and Quan [106] prescribed yellow filter to a multiple sclerosis patient with constant dizziness exacerbated with peripheral visual motion. The yellow lens increased the objective visual-cortical response, which was associated with positive subjective visual perception in this patient. In addition, the yellow lens helped the patient reduce symptoms of vertigo and improve his activities of daily living. In another study of 17 patients with multiple sclerosis, reading and visual search performance of patients who received a cover of their chosen color improved both when the covers were used and when they were not [107]. It appears that colored lenses may reduce visual symptoms in patients with VIMS by reducing visual stress, but further scientific studies are needed in this area.

5) Visual snow syndrome

Visual snow syndrome represents a constellation of visual and nonvisual problems, with the hallmark symptom presence of pixilated, scintillating, visual noise, nyctalopia, photopsia, and photosensitivity. Visual snow was typically constant and monochromatic. The most common etiology was mild traumatic brain injury. FL-41 lenses and blue tint filtered glasses often help relieve symptoms of patients. Approximately 80% to 90% of patients report symptom relief when using tints tailored to their specific visual sensitivities [108].

6) Stroke

Stroke is one of the causes of visual disturbances such as blurred vision, ocular motility, photosensitivity, visual processing, and reading difficulties. Beasley and Davies [109] used optimal spectral filters on reading performance following stroke in 17 patients. Spectral filters can immediately improve reading speed and accuracy following stroke, whereas prolonged use does not increase these benefits significantly. As a result, it should be noted that in some patients with neurological disorders such as visual snow syndrome and stroke, colored glasses may have benefits in improving visual and perceptual disorders, and it is best not to ignore them from the point of view of therapists.

7) Photosensitive epilepsy

Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns. Wearing tinted glasses can help manage the unpredictable nature of photosensitive epilepsy triggers [110].

In a study of 33 patients with photosensitive epilepsy, researchers performed colorimetric assessments. Most patients (70%) reported beneficial effects during the colorimetric assessment when prescribed glasses with tinted lenses. Pink or purple lenses predominated. Seventeen of the patients were available for a 2.4-year follow-up examination. Thirteen patients (57%) reported benefits and said they were still using the lenses. In some, the benefits included reduced dizziness caused by fluorescent light and the elimination of halos when using a computer screen. In seven cases, there was a reduction in seizures that could reasonably be attributed to the use of the lenses. In these patients, a modest reduction in electroencephalography light sensitivity with the use of tinted lenses [111]. Capovilla et al. [112] conducted a multicenter study at Italy on 610 patients with photosensitive epilepsy. They studied the effectiveness of Z1 lenses (a blue lens made of ultraviolet material with 80% reduction in the luminance of light frequencies between 550 and 700 nm) on photoparoxysmal response (PPR). Z1 lenses eliminated PPR in 463 patients and significantly reduced PPR in 109 patients. PPR remained unchanged in only 38 patients. The Z1 lens was highly effective in controlling PPR in a very large number of photosensitive epilepsy patients irrespective of their epilepsy or antiepileptic drug treatment. Blue Z1 lenses can dramatically reduce seizure frequency, with a substantial restriction in luminance that can limit their applicability in daily life. In one study, the efficacy of new blue lenses (Clarlet Z1 F133, Zeiss) with higher transmittance and reduced chromatic distortion in abolishing the PPR compared to the gold-standard Z1 lenses was investigated. These new blue lenses showed potentially greater tolerability, particularly in regions with fewer sunlight hours during winter [113].

Overall, the use of colored lenses such as blue Z1 lens in patients with photosensitive epilepsy is effective and leads to a reduction in symptoms. This lens may become a valuable resource in the daily practice of any physician caring for patients with epilepsy.

Conclusion

Adding special colors to eyeglass lenses not only helps patients, but also distinguishes the therapist from others. This seemingly simple method can help improve patients’ symptoms and increase their quality of life. The therapeutic effects of the lenses are related to improving contrast sensitivity, controlling brightness, and reducing photophobia. These lenses inhibit the transmission of short wavelengths of light and reduce the dispersion of the retinal image. Colored lenses reduce visual stress in neurological diseases that occur due to excessive excitability of the cerebral cortex and improve patients’ symptoms. So far, several studies have been conducted on the therapeutic effects of tinted lenses in the treatment of eye and neurological diseases. Most studies have methodology problems and researcher bias is observed in the results. Therefore, conducting scientific studies to prove the effects of colored lenses seems necessary. A summary of tinted glasses/filters in diseases is given in Table 2 [5,25,37,40,50,51,57,60,62,68–72,75,76,81,83,87–89,95–97,100,102–104,107].

Table 2.

Summary of tinted glasses/filters in diseases

Disease	Tint/filter	Function	Efficacy	Study type
Refractive error [40]	Yellow/pink	Increased contrast	Limited research (need further research)	Experimental study
Night driving [50,51]	Yellow	Increased contrast	Probably in young, need further research in real space	Comparative study [50] Cohort study [51]
Sleep quality [57]	Blue blocker	Filter out short wavelength	No clinical improvement	Systematic review
Dyslexia [60]	Irlen tint	Reduced visual stress	No reliable evidence	Systematic review
Ocular pain [62]	FL-41 lens (rose tint)	Decreased photophobia and light-induced brain activity	Reliable but need further research	Prospective case series
AMD (dry) [68–72]	Yellow/orange, LVI 527 filter, blue blocking	Increased contrast, decreased glare	Controversy results	Experimental study [68–71] Prospective and longitudinal study [72]
Retinitis pigmentosa [75,76]	Blue blocker, yellow	Minimal increased contrast sensitivity in low illumination	Controversy results, need further research	Experimental study [75] Cross-sectional study [76]
Albinism [76,83]	Neutral density filter	Decreased photophobia	Limited research (need further research)	Cross-sectional study [76] Experimental study [83]
Cataract [81]	Brown/yellow	Decreased glare	Limited research (need further research)	Experimental study
Post-refractive surgery [37]	Yellow	Decreased glare	Limited research (need further research)	Experimental study
Migraine [25,87–89]	FL-41 lens, 480- or 620-nm filter	Suppress of ipRGCs	Reliable	Experimental study [87,88] Randomized double-masked study [25,89]
Cluster headache [5]	Yellow-green	Suppress of ipRGCs	Need further research	Case report
Acquired brain injury [95–97]	CPF lens, gray, blue	Improved letter contrast sensitivity, reduced photophobia	Reliable	Cross-sectional study [95] Experimental study [96,97]
Visually induced motion sickness [102,103]	Yellow	Reduced visual stress	Limited research (need further research)	Case report [102] Experimental study [103]
Visual snow syndrome [100]	FL-41lens, blue tint filter	Reduced visual stress	Limited research (need further research)	Review of multiple experimental studies
Stroke [104]	Optimal spectral filters	Reduced visual stress	Limited research (need further research)	Experimental study
Photosensitive epilepsy [107]	Z1 lens (blue)	Control of photoparoxysmal response, reduced photophobia	Reliable	Multicenter study [107] Experimental study [106, 108]

AMD = age-related macular degeneration; ipRGC = intrinsically photosensitive retinal ganglion cell; CPF = Corning Photochromic Filters.