1st case of extreme light sensitivity in FA patient reported
Woman, 64, 'unique,' say researchers, calling for further study
Researchers in a report described the first case of a Friedreich’s ataxia (FA) patient who developed photophobia, or an extreme sensitivity to light.
A functional MRI scan of the 64-year-old woman showed abnormal brain activity in response to light stimulus compared with a scan from a non-FA patient with photophobia, the researchers said.
“This case highlights photophobia as a possible ocular presentation of [FA] and introduces the idea of visual [brain] dysfunction as a potential consequence of disease,” they wrote.
The case study, “Abnormal visual cortex activity using functional magnetic resonance imaging in treatment resistant photophobia in Friedreich Ataxia,” was published in the American Journal of Ophthalmology Case Reports.
FA is a genetic disease primarily affecting the spinal cord and cerebellum, the structure at the back of the brain involved in muscle control, including balance and movement. The hallmark FA symptom is ataxia, or a loss of coordination, while other symptoms include speech difficulties and heart problems. Many FA patients experience eye-related abnormalities, such as involuntary eye movements (nystagmus) and damage to the nerves connecting the eyes to the brain, but these symptoms don’t often lead to significant vision problems.
Worsening photophobia prompts clinic visit
A team led by researchers at the University of Miami described the woman’s case.
She was diagnosed with FA 36 years before arriving at the clinic with worsening photophobia, which arose spontaneously and had continued for about three years. She also had blurred vision, limited peripheral vision, and intermittent double vision (diplopia). She was on medication for irregular heartbeats and major depressive disorder.
Nine years before, she had undergone cataract extraction and lens implantation in both eyes. The surgery was complicated by swelling in a part of the retina (cystoid macular edema) in the right eye and epiretinal membrane, a tissue-like scar that forms on top of the retina, in both eyes. A few years later, the lenses dislocated in both eyes. The left-eye lens was repositioned without improvement in light sensitivity.
Vision tests showed impairment in both eyes. Nystagmus was previously documented but not noted during the examination. There were signs of damage to the optic nerve, severe symptoms of dry eye, and light sensitivity.
Tinted contact lenses and pilocarpine, a medication used to treat dry mouth and eye conditions, were tried, but the woman’s light sensitivity did not ease. Given her history of migraines, non-invasive brain stimulation therapy (external trigeminal nerve stimulation) was tested for three months, with no relief.
Functional MRI was then used to assess brain activity, as indicated by blood flow and oxygenation, in response to a light stimulus.
Testing involved two visual conditions: a black screen with a white cross and a white screen with an overlaying black cross. The woman was shown 16 episodes of the white screen for six seconds each, with the black screen in between. The researchers compared her results with those from a 41-year-old woman with severe, migraine-associated light sensitivity.
In the non-FA patient, light stimulus triggered an immediate blood oxygen response, followed by a fall to pre-stimulus levels in the first and second half of the scans. In the FA patient, the response was delayed and prolonged in the first half of the scan. In the second half, it became more delayed and continued to rise instead of falling to pre-stimulus levels.
As a treatment option, the team tried injecting botulinum toxin A (botox) into the skin on woman’s forehead because a previous study had used it to treat migraines. Six weeks later, however, she continued to experience light sensitivity.
“Our patient is unique as no prior reports have documented severe photophobia in patients with [FA],” the researchers wrote. “Future studies are needed to more robustly examine our findings.”
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