At a glance......
- 1 Mechanism of Photophobia
- 2 Causes of Photophobia
- 3 Symptoms of Photophobia
- 4 Diagnosis of Photophobia
- 5 Treatment of Photophobia
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Photophobia is reported in almost all forms of migraine and many neuro-ophthalmic disorders. The symptom is a hallmark of primary eye conditions such as uveitis as well as certain retinal dystrophies. It is included as one of the major criteria for migraine in the International Classification of Headache Disorders [rx, rx]. It is listed as a major symptom in blepharospasm. Yet in other clinical settings, some have suggested that photophobia is merely a functional symptom without an organic basis [rx].
Photophobia is a symptom of abnormal intolerance to the visual perception of light.[rx] As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical sensitivity of the eyes,[rx] though the term is sometimes additionally applied to an abnormal or irrational fear of light such as heliophobia.[rx]
Mechanism of Photophobia
Since light is the cardinal stimulus for photophobia, photoreceptors must be involved. There are at least five different types of photoreceptors in humans: three kinds of cones, rods, and ipRGCs. Rods and cones in the outer retina are the predominant photoreceptor cells of the mammalian retina. Their high temporal and spatial sensitivity to light forms the basis of image-forming vision. The intrinsically photosensitive retinal ganglion cells (ipRGC), which contain the melanopsin photopigment (HUGO gene symbol OPN4), have been identified in recent years [rx]. The ipRGC cells are atypical retinal photoreceptors separate from classical rod and cone photoreceptors. Several studies demonstrated that ipRGC play an important role in non-image-forming light effects [rx]. The ipRGC cells send their axons to the suprachiasmatic nucleus and the Edinger-Westphal nucleus. In the suprachiasmatic nucleus, these cells entrain circadian rhythms [rx]. In the Edinger-Westphal nucleus, they control the pupillary light reflex [rx, rx, rx]. Furthermore, evidence accumulating from animal models shows that ipRGCs are involved in photophobia of rod- and cone deficient mice. [rx, rx]. In humans, ipRGCs were implicated in photophobia since migraine patients who became blind from a complete lack of rod and cone function still experience photoallodynia compared with patients with enucleated eyes [rx]. Melanopsin, the ipRGC photopigment, has peak sensitivity at 480 nm. Using the photic blink reflex, one study tried to objectively quantify the ocular sensitivity to red (640 nm) and blue (485 nm) light in patients with light sensitivity and normal subjects. The data demonstrated an increased photic blink reflex to blue light as opposed to red light in light-sensitive patients [rx]. These results suggest that the melanopsin signaling system may control light aversion and the ipRGC may be the most important photoreceptor cell in the pathophysiological mechanism of photophobia.
Although the discovery of the ipRGC cells appear to make an advancement in understanding the mechanism of photophobia, how light functions as a pain stimulus remains elusive. Increasing evidence demonstrates that at least 3 pathways can transmit this signal to the brain. The first pathway was described by Okamoto et al. [rx]. They investigated the pattern of neuronal activation in the caudal brainstem after bright light stimulation using quantitative Fos-like immunoreactivity in anesthetized rats. The results showed that light activated the trigeminal brainstem neurons through photoreceptors in the retina (whether rod, cone or ipRGC), which in turn evoked ocular vasodilation and activation of pain-sensing neurons on blood vessels [rx]. The second pathway for photophobia is a direct connection between the ipRGC cells and thalamic nuclei, which are associated with somatic sensation and pain [rx]. The discovery of this second pathway is particularly significant as the thalamus is an important center for sensory integration, and has important connections to somatosensory centers of the cortex [rx]. A third pathway is suggested that does not involve the optic nerve. The ipRGCs and/or ipRGC-like melanopsin-containing neurons in the iris can contribute to the trigeminal afferents bypassing the optic nerve [rx, rx].
Neuropeptides that enhance synaptic transmission may play a role in photophobia at multiple levels of the visual and trigeminal pathways. Two particular candidates are the calcitonin gene-related peptide (CGRP) and pituitary adenylate cyclase-activating polypeptide (PACAP), both of which may play a role in migraine attacks in migraineurs [rx]. These multifunctional peptides are widely distributed in the nervous system and in addition to their vascular actions; they are both implicated in modulating nociception. Pre-clinical studies have linked both neuropeptides to photophobia. Animal models showed that mice with a gain-of-function mutation of the CGRP receptor, exhibit light avoiding behavior when they receive injections of calcium gene-related peptide [rx]. Mice lacking PACAP do not develop a nitroglycerin-induced light aversion.
Causes of Photophobia
Patients may develop photophobia as a result of several different medical conditions, related to the eye, the nervous system, genetic, or other causes. Photophobia may manifest itself in an increased response to light starting at any step in the visual system, such as:
- Too much light entering the eye. Too much light can enter the eye if it is damaged, such as with corneal abrasion and retinal damage, or if its pupil(s) is unable to normally constrict (seen with damage to the oculomotor nerve).
- Due to albinism, the lack of pigment in the colored part of the eyes (irises) makes them somewhat translucent. This means that the irises can't completely block light from entering the eye.
- Overstimulation of the photoreceptors in the retina
- Excessive electric impulses to the optic nerve
- Excessive response in the central nervous system
- Elevated trigeminal nerve tone (as it is sensory nerve to eye, elevated tone makes it over reactive). Elevated trigeminal tone causes elevated substance P which causes hypersensitivity. Often due to jaw misalignment.[rx]
Common causes of photophobia include migraine headaches, TMJ, cataracts, Sjogren's Syndrome, Mild Traumatic Brain Injury (MTBI), or severe ophthalmologic diseases such as uveitisor corneal abrasion.[rx] A more extensive list follows:
Causes of photophobia relating directly to the eye itself include:
- Anticholinergic drugs may cause photophobia by paralyzing the iris sphincter muscle.
- Cone dystrophy
- Congenital abnormalities of the eye
- Viral conjunctivitis[rx]
- Corneal abrasion
- Corneal dystrophy[rx]
- Corneal ulcer[rx]
- Disruption of the corneal epithelium, such as that caused by a corneal foreign body or keratitis
- Ectopia lentis
- Eye trauma caused by disease, injury, or infection such as chalazion, episcleritis, keratoconus, or optic nerve hypoplasia
- Hydrophthalmos, or congenital glaucoma
- Isotretinoin has been associated with photophobia[rx]
- Optic neuritis
- Pigment dispersion syndrome
- Pupillary dilation (naturally or chemically induced)[rx]
- Retinal detachment
- Scarring of the cornea or sclera
Neurological causes for photophobia include:
- Autism spectrum disorders[rx]
- Chiari malformation
- Encephalitis including Myalgic encephalomyelitis
- The trigeminal disturbance causes central sensitization (hence, multiple other associated hypersensitivities. Causes can be a bad bite, infected tooth, etc.[rx]
- Subarachnoid hemorrhage [rx]
- Tumor of the posterior cranial fossa
- Ankylosing spondylitis[rx]
- Drug withdrawal
- Ehlers-Danlos syndrome[rx]
- Infectious mononucleosis[rx]
- Magnesium deficiency[rx]
- Mercury poisoning[rx]
- Tyrosinemia type II[rx]
- Superior canal dehiscence syndrome[rx]
Symptoms of Photophobia
- Sensitivity to light is the inability to tolerate light, medically known as photophobia. In someone who is light sensitive, any type of light source (sunlight, fluorescent light, incandescent light) can cause discomfort.
- Photophobia typically causes a need to squint or close the eyes, and headache, nausea, or other symptoms may be associated with photophobia. Symptoms may be worse with bright light. People with light-colored eyes are more likely to have a sensitivity to bright light than those with darker-pigmented eyes.
- Light sensitivity is caused by a number of conditions that affect the eye (such as iritis, uveitis, and keratitis), as well as conditions that affect the entire body. Migraine headache is a common cause of photophobia, with a majority of migraine sufferers reporting sensitivity to light.
Diagnosis of Photophobia
The sequence of Events for Frequency-Specific Photophobia Assessment
- A standard penlight is shined in each eye with no glasses on. This is performed inside with normal indoor lighting.
- Observe responses to the light.
- Wait for the patient's photophobia to abate and ask him or her to recall the discomfort or pain experienced. This is a subjective measure of better, worse, or the same.
- Have the patient put on a pair of colored glasses.
- Shine the light into each eye.
- Note the response.
- Have the participant report whether the colored glasses made the light discomfort better, worse, or the same.
- Place the glasses in 1 of the 3 categories: better, worse, or the same.
- Repeat with the other colors.
- Colors tested are red, green, blue, violet, rose, indigo, orange, yellow, aqua, turquoise, pink, plum, and magenta. (These colors are presented here as a list and not in the order followed.)
- At the end of the examination, there should be 2 or 3 groups of glasses: glasses that had no benefit, glasses that made the photophobia worse, and glasses that made it better.
- Note the colors that mitigated photophobia symptoms.
- Have the patient wear each pair of colored glasses that provided some relief and perform activities such as walking around in a well-lit room, looking at electronic media, or reading from a book. Choose appropriate ADLs for the patient to test.
- Alternate the colored glasses with another pair that provided relief and repeat the process from step 13.
- Have the patient report whether any of the colors were more or less objectionable when executing ADLs.
- Recommend the patient consider purchasing glasses in 1 or more colors that provided relief. Remind the patient that environments can be lit differently and, therefore, suitable colors for each environment may also differ, so it is beneficial to have more than 1 color option available. Also, recommend that the purchased glasses should provide the maximum amount of physical coverage of the eyes and not just the visual fields. Thus, wide-rimmed glasses that cover the peripheral visual fields are recommended. Colored glasses can fit over prescription glasses as needed.
Colored glasses were assessed beginning with red, blue, and green because these are the 3 colors sensed by the cones. The remaining colors (listed in item 10) were tested in no particular order.
Treatment of Photophobia
There is only little evidence that shows that systemic medication can relieve the photophobia itself, but treating the underlying conditions may improve the associated photophobia, such as migraine preventive or specific medication (e.g., beta-blockers, calcium channel blockers, anticonvulsants, CGRP-P) for patients with migraine-associated photophobia [rx, rx, rx].
- Rest and medications are used to treat migraine headaches.
- Antibiotics are prescribed if conjunctivitis is present.
- Mild encephalitis typically requires bed rest, anti-inflammatory medications, and fluids. In severe cases, breathing assistance and other supportive care may be necessary.
- If a subarachnoid hemorrhage is present, the doctor will perform surgery. They will relieve the pressure by removing excess blood that has accumulated.
- Scleritis is typically treated with eye drops that work to decrease inflammation.
- If mild dry eye syndrome is present, artificial tears are given.
- If there is a corneal abrasion, the doctor usually prescribes antibiotic eye drops.
- If viral meningitis is present, rest and fluids are typically recommended.
Use and misuse of tinted lenses
- One principal treatment - is to decrease the dark-adapted state. Patients with severe photophobia who wear darkly tinted lenses should be encouraged to reduce dark adaptation. Chronic darkness will increase the perception and pain of light sensitivity. Lebensohn [rx] cautioned that “tinted glasses as a symptomatic remedy for chronic photophobia are to be condemned because of both their ineffectiveness and their habit-forming tendency”. Wearing sunglasses to an eye clinic has led many physicians to consider the patient to have some type of psychiatric disorder, or at least to predict nonorganic visual loss [rx, rx].
- Some optical tints have been tried successfully - to combat photophobia. Red-tinted contact lenses have been tested in individuals with photophobia due to cone disorders [rx–rx]. However, red tint appears to exacerbate migraine-associated photophobia [rx].
- Sunglasses - do make sense in the bright sunlight for patients with migraine, tension-type headaches and those with light sensitivity. Some tints have been successful in migraine. Good et al. [rx] found that FL-41 tint, a rose-colored tint, reduced migraine frequency in children by over one-half.
- Treatment of dry eyes - Aggressive treatment of dry eyes may be helpful. In blepharospasm, associated dry eyes are commonly treated with drops and ointments, and possible punctual plugs [rx].
- Anti-inflammatory drops - have been tested in reducing light sensitivity after cataract surgery and have not been found to be helpful [rx]. Xylocaine has been used after cataract surgery without a decrease in light sensitivity [rx].
- Dilating drops - Cycloplegics can be used to give some relief in patients with ocular inflammation. This is likely due to a reduction in ciliary muscle spasm since papillary dilation actually increases light entering the eye.
- Systemic medications - Sedatives (eg barbiturates) that reduce “trigeminal irritability” are helpful and allow for prolonged sleep and closed eyes [rx]. Treatment of migraine-associated photophobia with migraine preventive medications including beta-blockers, calcium channel blockers, and anti-convulsants is reasonable [rx]. Acute migraine should be treated with migraine-specific medications that have been shown to reduce photophobia associated with an acute attack [rx]. To the extent that other photophobic disorders are due to dysfunctional excitation/inhibition balance, migraine preventives, especially of the antiepileptic class, might be considered. Systemic medications that have been anecdotally reported to reduce the pain associated with photophobia include gabapentin and melatonin.
- Botulinum neurotoxin (BoNT) - is the treatment of choice for blepharospasm and it also has some efficacy in migraine headache. However, there is limited information for the effect of BoNT on photophobia. A cohort study showed that injection of onabotulinumtoxinA is helpful for photophobia associated with TBI . However, the efficacy needs to be further explored in well-designed studies involving a large population of patients. More work is necessary to evaluate the efficacy of the BoNT in the treatment of photophobia in other conditions as well 
Typical Instructions for an Athlete With Photophobia
Typical instructions given to an athlete with frequency-specific photophobia are as follows:
- Wear dark sunglasses at all times when outside during daylight.
- Wear the recommended colored glasses when inside or using a computer or bright electronic device. If multiple color options were useful, try to rotate through the colors that provide the best benefit and symptom mitigation on the basis of the environmental lighting. Colored glasses should not be worn while driving. If practical, apply translucent screen covers in the same colors as the glasses to serve as an additional filter or to replace colored glasses entirely when using electronic media. For example, in some settings (eg, schools), it is more socially acceptable to use a screen cover than to wear colored glasses. Modifying the hue using electronic settings is also an option.
- If possible, when using computers and other light-emitting media, dim the light intensity without decreasing the contrast. The dimming level is appropriate when an asymptomatic individual can easily read the screen.
Wear wide-brimmed hats at all times when outside during daylight.
- Avoid wearing dark sunglasses (traditional sunglasses) when inside.