Exactly, what is photophobia? It turns out it is not so clear, even for the scientists. Photophobia symptoms are obvious and form part of the definition of the condition. However, when you need a photophobia treatment, it gets complex. In many cases it is very difficult, when not impossible, to determine what causes photophobia. Here is the abstract of a recent (2012) overview of the most relevant photophobia research titled Shedding Light on Photophobia:
“Photophobia is a common yet debilitating symptom seen in many ophthalmic and neurologic disorders. Despite its prevalence, it is poorly understood and difficult to treat. However, the past few years have seen significant advances in our understanding of this symptom. We review the clinical characteristics and disorders associated with photophobia, discuss the anatomy and physiology of this phenomenon, and conclude with a practical approach to diagnosis and treatment.”
Recently I found this article by K.B. Digre, MD and K.C. Brennan, MD (published in the Journal of Neuro-Ophthalmology) which is a thorough overview of the state of the photophobia related research. Since GLARminY is principally about photophobia I am sharing its main points to provide an informed answer to What is photophobia. This (relatively long summary) is divided into the following subsections: photophobia definition, photophobia symptoms, photophobia causes, and (comming up next) photophobia treatment.
What is photophobia: Photophobia definition
The term photophobia is not the best choice for the condition it is describing. The Greek word phobia implies fear of or dread of hence: fear of light. However, “photophobia [is] abnormal sensitivity to light, especially of the eyes where exposure of the eye to light definitely induces or exacerbates pain. (…) While photophobia can undoubtedly be associated with factitious disorders, it is unlikely to be a purely ‘psychiatric’ symptom”. Photophobia, therefore, has nothing to do with fear of light. Instead “photophobia is a sensory state in which light causes discomfort in the eye or head; photophobia may also cause an avoidance reaction without overt pain. (…) Photophobia is intimately, likely inextricably, linked to pain sensation.”
Curiously, photophobia may also be experimented by the blind!
There are different levels of photophobia determined by light sensitivity threshold. Most studies show that “there are individual ‘thresholds’ of light sensitivity [displaying] some normal variation”. People with photophobia show lower thresholds of pain induced by light.
“Light sensitivity might also vary by season” with lower threshold of pain in winter months. There are some other circumstances that might lower a person’s threshold of light sensitivity: binocular as opposed to uniocular viewing, state of dark adaptation, shorter light wavelengths (blue), sometimes longer light wavelengths (red).
An important observation of one study is that photophobia adversely affects a person’s quality of life. Half of the adults in the study were unemployed! And about 25% felt that photophobia reduced their ability to lead a normal life!
What is photophobia: Photophobia symptoms
The authors clearly state that photophobia is a symptom. They never speak of photophobia symptoms, perhaps to avoid speaking of symptoms of a symptom. Still, the definitions imply the following photophobia symptoms:
- “exposure of the eye to light definitely induces or exacerbates pain”,
- “discomfort of the eye or head [caused by light, which] might also cause an avoidance reaction without overt pain“.
Hence photophobia symptoms revolve around the discomfort or pain caused by light. However, the authors distinguish between photophobia and photo-oculodynia, which is “light-induced eye pain from normally non painful source (e.g. ambient lighting)”.
What is photophobia: Photophobia causes
Photophobia causes are not easy to diagnose. However, one study showed that a cause can be found in the majority of adults, but very seldom in children. In a separate post I reproduce Table 1: Conditions associated with photophobia from the article. The list is long and I follow the classification of photophobia causes as proposed by the authors.
Rather than speaking of photophobia causes, the authors use the term associated conditions. The term association is used when there is uncertainty about direct causation of a condition – the researchers do not understand how a condition causes photophobia. Unfortunatelly this is the case for most of the conditions. It is also puzzling that some conditions cause photophobia only in the case of some people.
Conversely, there are other conditions (fewer), for example migrane, which are known to cause photophobia in most people. In these cases the authors explicitly state that these conditions induce or cause photophobia. Since (according to Google) most of us are interested in photophobia causes I have reclassified the conditions among photophobia causes and conditions associated with photophobia:
Conditions explicitly recognized as photophobia causes
(Note that although listed under photophobia causes, the conditions listed below do not always cause photophobia.)
- Anterior segment disease: iritis, cyclitis, blepharitis, dry eyes and dry eyes syndrome (a very common cause of photophobia), corneal neuropathy;
- Intreacraneal conditions: meningeal irritation from meningitis, sub-arachnoid hemorrhage, or pituitary tumors or apoplexy;
- Migrane (the most common photophobia cause);
Conditions associated with photophobia
- Posterior segment disease: retinal dystrophies, retinitis pigmentosa, cone dystrophies, hemeralopia, frequent photopsias, Alström syndrome;
- Headache type conditions: tension headache, cluster headache, hemicrania continua, other trigeminal autonomic cephalalgias;
- Traumatic Brain Injury (TBI);
- Progressive Suparnuclear Palsy (PSP);
- Psychiatric conditions: agoraphobia, seasonal affective disorder, bipolar depression, neurasthenia – a.k.a. chronic fatigue (there appears to be a powerful influence of affective circuits on photophobia), anxiety, panic disorder
I would encourage those who really want a through answer to What is photophobia read the section Anatomy and Pathophysiology of Photophobia (I considered it beyond the purpose of this post so I left it out).
In the next post I will cover the last section; diagnosing photophobia and photophobia treatment.
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