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C-42985

Eye-related photophobia

Photophobia has a variety of causes, including the result of eye or brain disease, or it can be a side effect of various drugs or laser surgery. It can also be a symptom of a more serious disorder such as meningitis and, therefore, requires appropriate investigation, diagnosis and treatment

Introduction

Photophobia is the experience of discomfort affecting the eyes as a result of exposure to light. Many individuals experience sensitivity of their eyes to sunlight and, consequently, wear sunglasses to protect their eyes. In these circumstances, the sensation of photophobia may not be related to any causal illness or specific eye problem. In more severe types of photophobia a specific cause can usually be identified. Hence, in a chart review of 111 adults attending an eye clinic with photophobia, a cause was found in the majority of the adult cases with ‘dry eyes’ being the most frequent presenting symptom.1 In addition, approximately 25% of the adults in the study reported that photophobia affected their quality of life.1 

Photophobia may be a useful sign distinguishing severe from more benign pathology.2 Hence, photophobia is a feature of most forms of migraine, can be a consequence of stroke,3 and can be associated with various neuro-ophthalmological conditions.4-6 Photophobia can also develop as a consequence of eye disease resulting from corneal damage, defects in pupillary constriction, or overstimulation of the retina and optic nerve. This article describes those photophobias which arise specifically from eye disease, affecting: the ocular adnexa; the cornea; the anterior eye, including developmental problems and inflammation; and the retina (see Table 1: Eye-related photophobia).

Ocular adnexa
Blepharitis 

Symptoms of blepharitis include red eye, flaking skin on lids, crusting of the lid margin, infection of eyelash follicles, and a sensation of a ‘gritty’ or itchy eye.7 Additional symptoms may include photophobia, abnormal eyelash growth, and loss of lashes. Less frequently, blepharitis can lead to physical alterations of the eyelid margin and vision loss due to superficial keratopathy.8 In a study of children in which blepharitis occurred in combination with kerato-conjunctivitis, photophobia was present in 52% of cases.9 Photophobia associated with blepharitis could be caused either by increased sensitivity of the anterior eye as a result of an infection or reduced control over light entering the eye due to impaired movement of the affected lid.

Blepharospasm

Blepharospasm is a focal dystonia associated with involuntary blinking, squeezing, or closure of the eyelids, and results from an imbalance in the excitation/inhibition mechanism of the brainstem eye blink reflex.10 Patients with blepharospasm can be as light-sensitive as those with migraine,11 approximately 80% of cases of photophobia reporting aggravated blepharospasm in bright light while driving, watching television, or reading.12 In addition, in a study of 316 patients with blepharospasm, 94% reported light sensitivity, with light at ambient levels provoking spasms, and 25% reported a severe limitation of their physical activity as a consequence.13 Photophobia in one form of blepharospasm, that is, benign essential blepharospasm (BEB), appears to be associated with abnormal hyperactivity of the thalamus of the brain which then causes excessive blinking.14 BEB may also be caused by over-activity of the superior sympathetic ganglion.15 Addition of photochromic lenses may allow patients with blepharospasm to tolerate significantly higher light intensities.16

The cornea

figure1 copyPhotophobia can result from a number of corneal problems including abrasion, ulcer (ulcerative keratitis), and dystrophy, and is often increasingly severe the more superficial the corneal damage.17 

Photophobia in these disorders is likely to be due to direct irritation of the trigeminal nerve. In addition, dry eye, which is commonly associated with photophobia, can lead to a corneal neuropathy.18 

Corneal abrasion

Corneal abrasion results in loss of the surface layers of the cornea usually as a consequence of trauma. Common symptoms include photophobia, pain, foreign body sensation, reflex tears, swelling, and blurred vision. Common causes include poking a finger into the eye, walking into a tree branch, grit in the eye followed by rubbing the corneal surface, and badly fitting or overuse of contact lenses. Similarly, refractive surgery can result in photophobia, especially if it involves making an incision into the cornea.19 

Corneal ulcer (ulcerative keratitis)

Corneal ulcer can damage both the epithelial and stromal layers of the cornea and is most common in tropical regions and in agricultural communities. It can be caused by a variety of trauma, chemical injury, or contact lens wear. Superficial ulcers involve a loss of part of the epithelium, while deeper ulcers may extend through the stroma causing severe scarring and even perforation. Location of the ulcer depends on cause. Hence, centrally located ulcers are often related to trauma, dry eye, or facial nerve paralysis. By contrast, disease involving the immune system can cause ulcers at the borders of the cornea or sclera, as in Mooren’s ulcer (see Figure 1: Section through a human eye showing Mooren's ulcer, which causes a crater-like depression of the cornea inside the limbus. Photophobia in this condition could result from direct irritation of trigeminal afferents. MU = site of ulcer; RD = retinal detatchment), a condition resulting in a circumferential ‘crater-like’ depression of the cornea located just inside the limbus, often with an overhanging edge. Ulcerative keratitis can be a painful condition due to nerve damage while increased tearing, vision loss, anterior uveitis, miosis, aqueous flare, and red eye may be signs and symptoms.

Corneal dystrophy

Photophobia is often associated with the corneal dystrophies, a group of rare mainly hereditary disorders, in which there is abnormal aggregation of lipids or cholesterol crystals in the cornea of both eyes. Corneal dystrophy usually presents in the teenage years or in the third decade of life and may not directly affect vision in its early stages. The condition is characterised by the appearance of ‘greyish white lines’ or ‘circles’ in the cornea causing increasing opacity. Over 20 different subtypes have been described with the signs and symptoms overlapping extensively. The visual impairment that results from these disorders is also highly variable and ranges from mild to severe. The extent of lipid or cholesterol deposition in the cornea could be an important factor contributing to photophobia as it may cause abnormal refraction and increased scattering of light within the eye.

Developmental problems of the anterior eye
Aphakia

Aphakia is the absence of a lens due to a congenital anomaly, surgical removal, perforating wound, or ulcer. The condition results in loss of accommodation, hyperopia, and a deeper anterior chamber than normal. Complications may include vitreous or retinal detachment and glaucoma. Individuals without a lens may see UV light in the range 300–400nm, which is normally excluded by the lens, and which is perceived as whitish blue or violet as a result of all three colour receptors of the retina being stimulated. The photophobia associated with this condition may result from this increased sensitivity.

Aniridia

figure2 copyAniridia is a condition in which the iris is either completely or partially absent. It is usually congenital although acquired cases may occur usually as a result of a penetrating injury.20 Vision may be severely compromised and the condition is often associated with nystagmus and photophobia.20 Photophobia in aniridia is likely to be a direct consequence of the loss of the iris tissue affecting control of light entering the eye. To attempt to block excessive light, coloured pigments have been introduced into the midstromal region of the cornea to create an artificial blue ‘iris.’21

Buphthalmos

Buphthalmos refers to the typical appearance of the eye in primary congenital glaucoma (PCG) (see Figure 2: Section through a human eye showing the various features of 'buphthalmos.' (AnC = enlarged anterior chamber; Co = enlarged cornea' OpD = cupped optic disc. The photophibia in this condition has multiple causes),22 a rare condition which usually appears at birth or within the first year of life, and accounts for between 0.01% and 0.04% of cases of total blindness.23 The impact on the visual development of a child can be severe and early recognition and appropriate therapy can significantly improve future quality of life. Typical clinical manifestations of PCG include photophobia, epiphora, blepharospasm, and a hazy enlarged cornea. Of these symptoms, photophobia is probably the most consistently present and can persist into adolescence. A cloudy cornea begins as a slight hazy opacity but later becomes more opaque with the development of stromal swelling. Increase in the size of the cornea is usually the result of a greater tension on the relatively elastic cornea and sclera of the infant eyeball and is often accompanied by a general enlargement of the eye. In addition, the anterior chamber becomes deeper, the pupil dilates, and the iris degenerates. The sclera is thin, often with a bluish tinge, the consequence of the uveal pigment showing through. Later the optic disc develops pallor, cupping, and becomes atrophic and without treatment often progresses to complete blindness. Hence, there are many changes in eye morphology in PCG and the exact cause of the photophobia is likely to be complex.

table1 copy

Coloboma

A coloboma is usually the result of a failure of the choroidal fissure to close completely during development.24 The condition can be unilateral or bilateral and most frequently involves the iris. Affects on vision can range from mild to severe and can be associated with photophobia, glaucoma, nystagmus, scotoma, and squint. The photophobia is likely to be a consequence of a reduction in the control of light entering the eye. Various techniques of intraocular lens implantation have been attempted to reduce photophobia in patients with iris and lens capsule colobomas.25 

Inflammation of the anterior eye

Photophobia can be associated with various types of inflammation affecting the internal structures of the eye, many being attributable to direct irritation of trigeminal afferents. Most commonly, photophobia is associated with uveitis, a condition also characterised by blurred vision, an irregular pupil, ‘floaters’ in the anterior chamber, and headache. By contrast, ‘endophthalmitis’ or ‘pan-uveitis’ describes inflammation affecting several internal membranes of the eye. The condition can occur as a complication of cataract surgery and usually has an infectious aetiology (see Figure 3: Section through a human eye in a case of 'pan-uveitis' or 'endophthalmitis' showing extensive inflammation of anterior eye structures. Photophobia in this condition could result from direct irritation of trigeminal afferents as a result of the inflammation. (AnC = anterior chamber; CB = ciliary body; Ir = iris)),26 while additional causes may include penetrating injury or the presence of a foreign body within the eye. The spread of infection via the blood stream can also be a cause especially in immunocompromised patients or those with diabetes. Endophthalmitis is frequently associated with photophobia, pain, loss of vision, and ‘red eye,’ while hypopyon may also be present.

The retina
Achromatopsia

figure3 copyAchromatopsia is a hereditary disorder of colour vision in which there is an inability to perceive colour and, consequently, to achieve satisfactory vision at high light levels. In its congenital form, there is a complete absence of cone cell activity, a condition also referred to as ‘rod monochromacy’ or ‘total colour blindness.’ A less severe form of the disorder is called dyschromatopsia, the most common symptom being ‘hemeralopia’ and as a result, achromatopsia frequently leads to photophobia.3 However, the cone system and the pathways carrying colour information appear to be intact, and it is the mechanism involved in perception of colour which appears to be defective in this disorder. The disorder is usually present in infants approximately six months of age and can often be identified by the presence of the photophobia and/or nystagmus, with the fundus often appearing normal. In its congenital form, there is a disruption of the retinal phototransduction pathway in which the cone cells do not respond to light by hyperpolarising. There is generally no treatment although experiments have been attempted involving a cybernetic device – the ‘eyeborg’ – which attempts to create the perception of colour using sound waves.27

Retinal detachment

Retinal detachment (RD) is classified into a number of subtypes: ‘rhegmatogenous’, in which there is a tear in the retina and fluid from the vitreous space leaks into the subretinal space; ‘exudative’, ‘serous’ or ‘secondary’ which results from inflammation, injury, or vascular abnormalities; and ‘tractional’ in which fibrous or fibrovascular tissue pulls the sensory retina from the retinal pigment epithelium (RPE).

RD is commonly preceded by a posterior vitreous detachment (PVD), which is identified by flashes of light or photophobia, floaters in the vitreous, and a feeling of heaviness in the eye. If PVD develops into retinal detachment, then a dense shadow is drawn over the visual field usually commencing at the periphery and moving towards the centre.

A particularly severe form of photophobia can result after vitreoretinal surgery in which a heavy silicone oil tamponade is applied.28

Retinal dystrophy

Photophobia may be a presenting feature of the retinal dystrophies in general and an early and frequent symptom of cone dystrophy,29 even before any visual loss is apparent.30,31 Unlike the anterior eye, the retina has no sensation and as such, there is likely to be a different explanation for photophobia of retinal origin. In some patients with cone dystrophy, enhanced rod activity has been observed consistent with retinal dysfunction, which could play a role in the photophobia.32 Although rods and cones are the primary light sensors of the eye, a separate set of photo-sensitive cells, the intrinsically-photosensitive retinal ganglion cells (IPRGC), have been discovered which use melanin rather than rhodopsin as a light-sensitive pigment.33 These cells project to the olivary, pretectal, and suprachiasmatic nuclei and may be involved in detection of day length and in maintenance of the circadian rhythm. Such light-sensitive cells may also be present in the iris.34 Hence, stimulation of these cells could be involved in photophobia of retinal origin especially when associated with retinal dystrophy. Red tinted contact lenses have been used to alleviate photophobia in some cone disorders.35

Treatment

Photophobia varies with season and optometrists will often advise the wearing of tinted spectacles to manage the problem. In more severe and persistent cases, it is necessary to determine the underlying cause. Hence, it may be necessary to treat the underlying disorder, to discontinue or change a particular drug regime, or modify contact lens parameters. Lifestyle changes may also help to reduce photophobia and patients should be advised to avoid smoking, to wear sunglasses outside, and to obtain a specific prescription for night driving. 

In addition, drugs are used to treat photophobia if it arises as a consequence of the use of mydriatics to dilate the pupil for eye examination, inflammation, or refractive surgery.19

Conclusion

Photophobia is a complex eye symptom ranging in severity from mild to severe and can result from multiple causes. Two major factors are likely to be responsible: direct stimulation of the trigeminal nerve due to damage, disease, or excessive light entering the eye; and overstimulation of the retina.

About the author

Dr Richard Armstrong was educated first at King’s College London and subsequently at St Catherine’s College, University of Oxford. His early research involved the application of statistical methods to problems in ecology and botany. He taught ecology for many years at the University of Aston before retraining in neurosciences at the Institute of Psychiatry in London and at the University of Washington in the US. Subsequently, he has taught biomedical subjects to optometry students at Aston University. His current major research interest is in the application of quantitative methods in the study of neurodegenerative disease.

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