Abstract

Photophobia is a sensitivity or intolerance to light, causing mild to severe discomfort, pain and the need to squint or close the eyes. It can be caused by all types of light sources, including fluorescent, incandescent light, and the bright rays of the sun. The author discusses a number of conditions wherein photophobia is an important symptom.

Introduction

Photophobia mostly occurs as a symptom, therefore the aim is to identify and treat the underlying condition. Photophobia is reported in many neuro-ophthalmic disorders and it is a distinctive feature of primary eye conditions such as uveitis and some retinal dystrophies^1,2.

Photophobia may be related to various underlying ocular causes, such asphotophobia due to too much light entering the eye, which includes conditions such as aniridia, coloboma of the iris and albinism. Photophobia also results from diffuse diffraction of light,which is caused by opacities of the refractive media, such as lens and vitreous opacities.  Nearly all ocular inflammatory diseases will lead to photophobia and photophobia may also occur without any obvious ocular conditions, such as photophobia experienced with migraine¹⁸.

Signs of photophobia include closure of one or both eyes, blinking frequently and epiphora, leading to ocular pain and headaches¹⁹.

Migraine

The onset of a migraine headache causes throbbing, which then intensifies with an increase in intracranial pressure. It presents in association with nausea, vomiting, abnormal sensitivity to light (photophobia), noise and smell.

Photophobia is one of the major criteria for migraine as per the International Classification of Headache Disorders^1,2. During an attack, up to 80% of migraine patients experience photophobia. A study has suggested that three factors, which include photophobia, disability and nausea, indicated a migraine approximately 98% of the time ³. Migraine attacks that are triggered by light or glare amount to between thirty and sixty percent. A migraine attack may be a reaction triggered by many other stimuli aswell. It may occur via the trigeminal nerve in refractive errors, heterophorias, or with optical stimulation when bright light and shadow alternate¹⁸. 

Photophobia is not restricted to the headache phase, but often it also occurs before and after the headache has subsided ⁷. A study had found that photophobia was more pronounced in migraine patients during attacks than outside attacks and that migraine patients, as opposed to controls, were more photophobic in general⁵.

In a study conducted in patients with normal eyesight, a comparison was made on the effect of the colour of light to indicate the level of increase or decrease in severity of a migraine. The results indicated that green light exacerbates migraine significantly less than white, blue, amber or red lights⁵. Furthermore, this study suggests that migraine photophobia could originate in cone-driven retinal pathways⁵.

Other effects of migraine headaches on the visual cortex, present with scintillating lights and scotomas⁵. If the visual disturbances predominate, the headache is called “ocular migraine”. Scotomas due to migraine headaches, mostly originate in an area close to the fixation point and then extends peripherally. Sometimes the scotoma may begin at the margin of the field and progress centrally. The restoration of the visual field follows the same sequence, with the part of the visual field first affected by the attack, being the first to clear¹⁸. Flicker scotomas like bright flickering dots, or dark figures, usually occur in one-half of the field and begin as defects in the field, usually lasting for 20 minutes. These visual defects can move around and cause micropsia (everything is seen minified). After these symptoms occur, the headache begins. Usually it isunilateral, above an eye, at the temple or at the occipital lobe¹⁸. Due to the frequency of hypersensitivity to light, it is advised that the patient’s room should be darkened.

Blepharospasm

Blepharospasm is both a cranial and focal dystonia, which is characterized by repetitive and sustained contractions of the orbicularis oculi and frontalis muscles bilaterally, causing the eyelids to close involuntarily. Patients report increased blinking as the initial symptom of blepharospasm, followed by involuntary eyelid closure, twitching of eyelids and then powerful or sustained eyelid closure. Symptoms of blepharospasm include dry eyes and squinting. Other diagnoses which occurred prior to the onset of blepharospasm include head trauma, depression, anxiety, glare and with diplopia¹⁷. Blepharospasm may also be caused as a reflex in all diseases of the conjunctiva, lids and the cornea. Blepharospasm also occurs in trigeminal neuralgia, Parkinsons disease, with brain tumours and intracranial abscesses, aneurysms, stroke and irritation after facial palsy¹⁸.

Blepharospasm usually occurs in the 5^th to 7^th decades of life and mostly affects women¹⁷. Childhood or adolescent onset of blepharospasm, without any obvious external eye causes, such as unilateral hemifacial spasm, bilateral orbicularis blepharospasm or intractable orbicularis myokymia, is very unusual. A full neurological assessment is indicated if blepharospasm is diagnosed in childhood¹⁹.

In a large survey on patients with blepharospasm, it was found that eighty percent reported aggravation of symptoms with bright lights, while driving, watching television or reading, which may interfere with these visual activities¹⁵. It was also found that patients with blepharospasm were just as light sensitive as patients with migraine, and both groups were more light sensitive than controls¹⁶.

Reflex blepharospasm, which results from bright light and other stimuli, can occur as a congenital familial characteristic. It occurs as prolonged spasms of forceful bilateral closure of the eyelids, in response to a stimulus that would normally cause a reflex blink¹⁹.

Some patients with primary blepharospasm found relief with a sensory trick (touching the face, pinching the skin, talking) or rest, but this was not documented in cases of secondary blepharospasm¹⁷.

Dry eyes

The eye is protected against damage and infection by the lids and a lubricating tear film. If the tear film is inadequate to wet the surface of the eye or if the tears evaporate rapidly, it results in dryness of the surface of the eye¹⁹. In essence, the dry eye is a compromised one and is prone to infection, delayed healing, and adverse effects from topical medication²⁰. This may be aggravated in a dry atmosphere. Insufficient blinking, which occurs during reading, the use of a computer and watching television, also tend to make the symptoms worse²⁰.

The most common eye-related cause of photophobia in adults is dry eye ¹³. Photophobia and dry eye can be uncomfortable and painful. Dry eyes begin at the ocular surface and include signs of tear instability, hyperosmolarity, inflammation and changes in tear composition. The terminal endings of corneal nociceptors are in close contact to the tear film and are thus sensitive to such changes ⁹. The prolonged nociceptive input creates an increased excitability and synaptic potentiation in the central nociceptive pathways ¹⁰. This creates a state of increased responsiveness to painful stimuli. Therefore central sensitization underlies some of the symptoms of photophobia in patients with dry eye. A neuroinflammatory response with activation of glia, also contributes significantly in the alteration of sensory signal processing by the central nervous system, thus causing them to be perceived as painful ¹¹. This happens in the trigeminal sensory system as well ¹². Therefore, a widespread hypersensitivity may create a perception of pain by the input of light (i.e. photophobia).

To test the stability of the tear film, Tear Breakup Time (TBUT) may be used as a diagnostic test, whereby fluorescein dye is placed on the surface of the eye. Dry spots will be observed in less than 10 seconds if there is tear instability. Dyes such as rose Bengal, fluorescein and lisamine green can be used to identify where ocular surface cells have been damaged from dry eye. The Schirmer test measures the amount of aqueous tears produced, whereby a strip of filter paper is placed at the edge of the eyelid for a standard period of time, which would usually be 5 minutes. The amount of tear volume that has been soaked into the filter paper is measured. Generally, a Schirmer test result of less than 5 mm is diagnostic of significant tear deficiency. Treatment for dry eyes include anti-inflammatory medication, tear supplements and medication to stimulate tear production.

Cornea

Corneal disorders are one of the most common causes of photophobia. The following are some of the conditions which may contribute to photophobia:

• Epithelial injury
  In the case of recent onset of severe photophobia with epiphora (excessive watering of the eyes), conjunctival hyperaemia and oedema of the eyelids, an epithelial injury should be suspected.An epithelial injury may occur with corneal erosions, foreign bodies, corneal burns or complications with contact lens use.A corneal erosion occurs when there is loss of corneal epithelium, resulting in a sharp pain, followed by a foreign body sensation, photophobia and tearing. These symptoms could last for 2 to 3 days and can occur repeatedly. Most often, spontaneous erosions occur upon awakening, because the eyes get dry at night and the eyelid can stick slightly to the epithelium. Although this could also occur at any time of the day or during sleep²⁰. Other erosions could occur due to direct impact from a foreign body, like grains of sand, soot, iron splinters, insect wings or lashes rubbing on the cornea (trichiasis). A foreign body could also be stuck in the upper lid (mostly in the sub-tarsal sulcus). Linear, vertical or oblique erosions, seen withfluorescein staining, are indicative of a foreign body that could be hidden in the upper bulbar conjunctiva or in the fornix¹⁸. Installation of topical anaesthetic would facilitate the examination to reduce pain and allow better patient cooperation. Fluorescein staining should be conducted in order to readily stain the abraded corneal surface and help to ensure the absence of penetration²⁰.
• Corneal stromal changes
  (a) Corneal scars are an important cause of photophobia, especially if the visual axis is affected. This is probably due to light scattering. On trans illumination, scars appear as dark spots in front of the red reflex of the pupil¹⁸. A light scar is called a nebula, while a more marked scar is called a macular, and a dense scar is called a leukoma¹⁸.
  (b) When deposition of materials such as cystinosis occurs, in cases of recurrent erosions.
  (c) Inflammatory diseases of the cornea (keratitis). There occurs disruption of the corneal surface in keratitis, therefore it is a very important cause of photophobia¹⁹. In addition, keratitis presents with injection, hyperaemia of the conjunctiva, lid oedema, pain, foreign body sensation, burning, tearing and blepharospasm¹⁸.

Uvea

The following are some abnormalities of the uvea which cause photophobia.

• Ocular and oculocutaneous albinism
  A significant degree of photophobia occurs with this condition, because the iris does not function in shutting out light¹⁸. Ocular albinism often presents with fundus changes (decreased pigmentation), so choroidal vessels become visible. Coarse granular, brownish pigment dissemination and deposition may also be present at the posterior pole and in the midperiphery¹⁸. Macular hypoplasia occurs in nearly all types of albinism, resulting in loss of visual acuity. Often there is presence of astigmatism and acuity can be 20/30 or better, or may be less than 20/200, depending on the type of albinism. Pendular nystagmus occurs with this condition as a result of amblyopia and macular hypoplasia.
• Aniridia
  Aniridia can be congenital where the iris may be completely or partially absent, or it may be acquired by a penetrating injury¹⁹. Congenital aniridia is a rare bilateral condition, but asymmetry between the two eyes does occur. It may have life threatening associations because it occurs as a result of abnormal neuroectodermal development. This is due to mutation of a gene which controls the development of a number of structures, thus the broad involvement of ocular and systemic conditions²³. At birth, aniridia presents with nystagmus, photophobia and the absence of irides or ‘dilated pupils’, which would be noticed by the parents²³. Decreased vision is a result of multiple factors which include light scatter, opacities of the cornea and lens, severe glaucoma, optic nerve hypoplasia, foveal hypoplasia and nystagmus¹⁹. At an appropriate age, opaque contact lenses may be used, to create an artificial pupil and improve vision and cosmesis²³.
• Uveitis
  This is inflammation arising from the iris, ciliary body or choroid, including conditions where there is primary involvement of the retina and retinal pigment epithelium¹⁹. Ocular inflammatory diseases, like uveitis, lead to photophobia due to diffuse diffraction of light. Anterior uveitis may be subdivided into two categories. One is iritis, which involves inflammation of the iris. The second is iridocyclitis, in which both the iris and ciliary body are involved. Acute anterior uveitis is the most common form of anterior uveitis, which typically presents with unilateral pain, photophobia and redness, which may be due to lacrimation. Acute anterior uveitis is characterized by sudden onset of symptoms, which last for a period of 3 months or less. Due to the severity of the symptoms, the patient will be forced to seek medical attention. Patients with chronic anterior uveitis are mostly asymptomatic, until complications such as cataract or band keratopathy develop.Intermediate uveitis involves inflammation occurring predominantly at the vitreous.Intermediate uveitis presents with insidious onset of blurred vision accompanied by vitreous floaters. Initially it is unilateral, but later affects both eyes.Posterior uveitis occurs at the fundus posterior to the vitreous base. Symptoms presented with posterior uveitis depend on the location of the inflammation and the presence of vitritis. A patient, for example, with a peripheral lesion may complain of floaterswhile a patient with a lesion which involves the macula will mostly complain of impairment to central vision.Panuveitis is diffuse, and involves the entire uveal tract²³.
• Iris coloboma
  A coloboma is when a part of an ocular structure is absent as a result of incomplete closure of the embryonic fissure. It may be a complete coloboma involving the entire length of the fissure or only part thereof (i.e. iris, ciliary body, retina and choroid or the optic disc)²³. Congenital iris coloboma usually occurs nasally and inferiorly with the pupillary margin frequently present at the edges of the coloboma. Acquired iris coloboma occurs as a result of accidental or surgical trauma. It is sharply delineated and the margin of the pupil does not extend into the area of the coloboma¹⁸. Photophobia will be experienced with too much light entering the eye.

Lens (Cataracts)

Protein accounts for thirty-five percent of the lens. Layers of different indices are separated by definite zones. The central embryonal nucleus will be occupied by the adult or senile nucleus with advancing age. The time when an opacity is formed can be indicated from its location relative to the zones of discontinuity (see Figure 1). Less water is contained in the older lens fibres, at the centre, than the peripheral ones.

Any lens opacity can be called a cataract¹⁸. According to the World Health Organization, cataracts are the leading cause of blindness among people over forty, worldwide²¹. With aging, a reduction of the focusing ability and transparency of the lens occurs, as a result of the long living crystalline protein that is continuously challenged by endogenous and exogenous agents. This drives the lens proteins to undergo a wide variety of alteration and part of the soluble proteins become insoluble¹⁸.  Eventually larger light scattering aggregates are formed. When these become clinically significant, it leads to the development of a cataract causing blurred vision. Patients feel as if they are looking through a dirty window. Congenital cataracts may also occur due to mutation in genetic materials. Congenital cataracts are frequently inherited as an autosomal dominant trait and less commonly as an autosomal recessive trait¹⁹. Traumatic cataracts occur as a result of injury to the eye. However, most cataracts are age related.

Cataracts can be broadly classified into nuclear cataract, cortical cataract and sub-capsular cataracts, based on the anatomic location and pathophysiology.

Photophobia and glare are symptoms experienced by patients with cataracts. Patients would see better at dusk, when there is dilation of the pupil, because they can look around central opacities¹⁸. Lenticular conditions that are most likely to lead to photophobia are partial cataracts, particularly posterior sub-capsular and lamellar or zonular cataracts, and ectopia lentis. Photophobia in zonular or lamellar cataract and in ectopia lentis is most likely due to light scattering or glare, while photophobia experienced with posterior sub-capsular cataract, with the significant impairment of vision, is most likely due to in-crossing illumination¹⁹.

Retina

Congenital cone dystrophy.

Photophobia is common in patients with congenital cone dystrophies. This retinal dystrophy presents in the first to second decade with gradual bilateral impairment of central and colour vision²³. Many patients that initially have cone dysfunction, have subsequent effect on the rod system, however the effect on the rod system is less severe²³.  The severity of cone dystrophies vary and are often associated with nystagmus. Many of these patients present a significant increase in visual acuity with decreased ambient illumination¹⁹. Signs of cone dystrophy include Bull’s-eye maculopathy, ‘bone-specule’ pigmentation in the mid-periphery, arteriolar attenuation, temporal disc pallor and progressive retinal pigment epithelium atrophy at the macula with eventual geographic atrophy²³.

Less common causes of photophobia

These include non-organic factors such as attention-seeking behaviour in children, with frequent blinking in association with peri-orbital pain, headache, diplopia and photophobia. In this case, the patient just needs compassionate reassurance.

It has been observed that people with very fair complexion will complain of photophobia. It is important to rule out ocular albinism in this situation¹⁹.

Conclusion

Finding relief from photophobia involves treatment of the underlying cause of light sensitivity. If an infection or an illness is the cause of the light sensitivity, treating it will often cease the photophobia symptoms.

While outdoors, relieving photophobia involves limiting harsh light sources. The use of a wide brimmed hat or sunglasses with ultraviolet protection would protect the eyes in harsh sunlight. The use of polarised sunglasses works very well for relieving photophobia. This will reduce the effects of the bright sunlight. In patients with severe photophobia, the use of prosthetic contact lenses would be advised. They are made to match the colour of the eye and they reduce the amount of light that enters the eye.

When indoors, reducing the symptoms of photophobia include limiting of bright light sources, by keeping the curtains closed to reduce the amount of sunlight entering through the windows. The use of dim light bulbs or dark lamp shades would also reduce bright light sources and ease the sensitivity to light.

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