Sensory disorders are common in those with traumatic brain injury (TBI), including anomalies of vision, audition, and olfaction [1-14]. In terms of vision anomalies, one symptom evident in those with TBI is photosensitivity, or photophobia, which presents as an elevated sensitivity to light in the absence of ocular inflammation or infection [7-14]. Photosensitivity in those with TBI has been reported in between 20-40% in non-selected (i.e., not necessarily visually-symptomatic persons with TBI) samples  and up to nearly 50% in selected (i.e., visually-symptomatic persons with TBI) . The type of photosensitivity may be: 1) generalized to all types of lighting, or 2) selective to fluorescent lighting.
This article serves to provide a brief overview of presenting symptoms and possible underlying neurology, as well as existing evaluative and treatment options.
Those with TBI with generalized photosensitivity  to all types of lighting may report the following symptoms when functioning in spaces illuminated with brighter lighting:
- fatigue with
- higher level cognitive tasks, including multi-tasking
- physical activity
- eyestrain and eye fatigue
- headache, which may or may not be migrainous
SELECTIVE PHOTOSENSITIVITY TO FLUORESCENT LIGHTING
Those with TBI, who present with selective photosensitivity  to fluorescent lighting, present often with visual-vestibular symptoms. They may report the following symptoms when functioning in spaces illuminated with fluorescent lighting:
- fatigue with:
- higher level cognitive tasks, including multi-tasking
- physical activity
- eyestrain and eye fatigue
- headache, which may or may not be migrainous
- disequilibrium, dizziness, and possible vertigo
- increased sensitivity to motion of visual stimuli (i.e., scrolling on computers, watching scrolling tabs on television, and watching fast-edit programs), as well as being in environments with multiple visual stimuli (i.e., crowded streets, busy malls, supermarkets)
POSSIBLE UNDERLYING NEUROLOGY
Although the precise neurological substrate responsible for photosensitivity in TBI has not yet been elucidated, working hypotheses have arisen over the years.
Ciuffreda’s research team investigated associated aspects of photosensitivity and reported their results in four papers [11-14].
Du et al.  studied scotopic threshold values, which refers to the intensity (starting with very bright and gradually reducing until the first magnitude of intensity which is not perceivable) of light not perceived after a person has pre-dark-adapted for 2 minutes. Du et al. reported elevated scotopic (or dark adaptation)thresholds in those with mild TBI presenting with photosensitivity.
Subsequently, Chang et al.  and Schrupp et al.  investigated critical flicker frequency threshold values. The term, critical flicker frequency threshold, refers to the minimal (or range of) magnitude of frequency of flicker resulting in the perception of steady-state (rather than flickering) presentation of light. Chang et al.  and Schrupp et al.  presented data illustrating critical flicker frequency thresholds in mild TBI to be relatively more elevated in those with photosensitivity and motion sensitivity.
Most recently, Patel et al.  studied coherent motion threshold, which refers to the quantitative assessment of a person's ability to detect motion in the absence of context. Patel et al. defined their coherent motion threshold as the minimal percentage of coherently moving dots (i.e., moving leftward or rightward), which are embedded within a larger matrix of dots moving randomly, required to be perceived accurately as "moving in the correct direction". Patel et al.  presented data revealing elevated coherent motion thresholds in symptomatic patients with mild TBI.
The results of these four papers [11-14] led Ciuffreda’s research team to hypothesize that anomalous cortical or subcortical regulation of response to changes in illumination and visual-spatial patterns, possibly mediated by the dorsal visual pathway, may be contributing to the perception of photosensitivity on those with TBI.
Another theory posed by Wilkins [15-23] is based on the concept of “visual stress”, which he describes as including the following vision symptoms:
b) visual-perceptual distortions:
i) apparent movement of print
ii) blurring or fading of letters
iii) colors appearing around words
iv) changes in spacing or perceived size of letters
v) patterns appearing in dark print or white space (may be reported as being worm-like in appearance)
vi) discomfort when viewing repeated bold patterns or stripes
In addition to the above vision symptoms, Wilkins describes that patients experiencing visual stress may also report the following symptoms in the presence of glare from a page or computer screen:
- dizziness, with or without nausea
- eye/head pain
Such symptoms resemble those reported by patients with TBI and photosensitivity. In fact, Wilkins [17-23] reports that persons experiencing glare and reading difficulties, who also have head injuries, seizures, or migraines, may be suffering from visual stress.
Wilkins’s working hypothesis [17,19-23] underlying the visual stress is that the associated visual perceptual distortions occur in response to a spread of cortical hyperexcitability, which may result in inappropriate firing of neurons related to visual processing and perception. Wilkins hypothesizes that:
- the cortical hyperexcitability is non-uniform.
- an increased magnitude of the hyperexcitability results in a corresponding increased susceptibility to visual stress symptoms.
- a systematic application of tinted color overlays or tinted color lenses may reduce the effective non-uniformity of the cortical hyperexcitability by re-distributing the cortical response to visual stimulation. This is possible because of the variable spectral sensitivity and topography of cortical neurons responding to color in the human cortex. A reduction in the non-uniformity of the cortical hyperexcitability concurrently improves visual comfort for reading and viewing multiply-visually stimulating environments.
Related to Wilkins’s theory regarding visual stress, Evans  reported on a possible optometric diagnostic tool, a pattern glare test, to assist in determining whether a person is experiencing visual stress. The pattern glare test  involves viewing three patterned targets at distinct spatial frequencies: 0.5 cycles per degree (cpd), 3 cpd, and 12 cpd. The pattern glare score is noted as either the:
a) sum of distortions reported with the 3 cpd pattern
b) difference between the number of distortions with the 3 and 12 cpd gratings (i.e., the 3-12 cpd difference).
The normal range of a pattern glare score for a person not experiencing visual stress would be <4 on the 3 cpd grating and <3 on the 3-12 cpd difference.
Evans  reported that those experiencing visual stress (such as migraineurs) presented with greater difficulty viewing all 3 gratings, relative to an age and gender matched cohort. Evans postulated that, using the pattern glare test, persons scoring >3 on the 3 cpd and >1 on 3-12 cpd difference are likely to be suffering from visual stress and may benefit from the systematic prescription of tinted lenses.
A complete vision evaluation including dilated fundus evaluation with a neuro-optometrist, ophthalmologist, or neuro-ophthalmologist is recommended for patients reporting photosensitivity to rule out structural ocular anomalies as causes for the photosensitivity, such as certain anomalies of the cornea, iris, lens, retina, and optic nerve. In addition to the traditional vision examination, a sensorimotor vision [10, 24, 25] examination including ocular alignment, ranges of accommodation and vergence, color vision, automated visual field testing, as well as threshold measurements of contrast sensitivity, scotopic sensitivity, critical flicker frequency, coherent motion, and pattern glare for comparison to normative data. Anomalies in thresholds for contrast sensitivity, scotopic sensitivity, critical flicker frequency, coherent motion, and/or pattern glare relative to the normative data may corroborate the symptom of photosensitivity.
Although photosensitivity in those with TBI may or may not resolve on its own, providing some means of alleviating the symptoms by prescribing tinted lenses, use of colored overlays, and recommending the wearing of brimmed caps (to block the illumination and visual stimuli from above) benefits the symptomatic patient [9-23, 25]. However, for many practitioners, determining the tint color and percentage of tint (usually with lighter percentages of tints for indoors and darker tints for outdoors) has been largely subjective and patient-dependent. Lenses which change percentage of tint gradually depending upon illumination, also referred to as “transition” lenses, have improved in design and functionality over the years, and eye care providers are prescribing them with increasing frequency for their photosensitive patients. Prescribing colored overlay filters for use over reading materials and computer screens can also benefit the photosensitive patient. However, these traditional approaches do not consistently result in improved comfort and function for patients.
Over the past decade, researchers have sought to develop and research more systematic means of prescribing tinted lenses, with one of the more favored approaches involving colorimetry [15, 16, 20-22]. Colorimetry is a means of determining the precise hue and percentage of hue resulting in reduced visual stress for the patient . The color and percentage of the tint may or may not be similar to a colored overlay selected by a patient, so color overlays should not be used as a definitive guide to prescribing tinted lenses. However, if colored overlays have been tried with a patient with benefit, then it is appropriate to systematically select a color and tint using a colorimeter. The type of colorimeter that has been reported on in the literature is the Intuitive Colorimeter [15, 16, 20-22].
A colorimeter [15, 16, 20-22] is a device, which shines colored lighting onto a page of text, permitting the independent variance of color hue and saturation while maintaining brightness constant. Using successive approximation of the color by altering the hue and saturation while under conditions of color adaptation, one can estimate the color hue and color saturation resulting in reduced symptoms of visual stress. The required color and saturation may be incorporated into a trial of tinted lenses for assessment in the patient’s habitual room illumination. The tint of the trial lenses may be adjusted slightly to optimize the patient’s comfort and function, after which a prescription may be written for spectacle lenses, including the lens and/or prism power required for the patient.
Photosensitivity, also reported as photophobia, is a common symptom in those with traumatic brain injury, usually occurring in the absence of ocular inflammation or disease. Photosensitivity may be: 1) generalized to all types of lighting, or 2) selective to fluorescent lighting. In addition to a standard vision examination with dilation to rule out structural ocular and functional vision anomalies, results of specialized evaluative procedures including sensorimotor vision testing (specifically, threshold measurements of contrast sensitivity, scotopic sensitivity, critical flicker frequency, coherent motion, and pattern glare) when compared to normative data may corroborate the symptom of photosensitivity. Treatment options remain non-standardized in terms of arriving systematically at an appropriate tint or colored lens overlay, but there are systems, which are being studied, including colorimetry. Larger, longitudinal studies investigating the efficacy of treatment options on thresholds of scotopic sensitivity, contrast sensitivity, critical flicker frequency, coherent motion, and pattern glare may prove beneficial for developing a standardized approach in the treatment of photosensitivity in TBI.
About the Author
Corresponding author’s contact information:
Neera Kapoor, OD, MS
Associate Clinical Professor
Chief, Vision Rehabilitation Services
State University of New York’s State College of Optometry
Department of Clinical Sciences
33 West 42nd Street
New York, NY 10036
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