Photosensitivity Dr. Cathy Stern, OD, FCSO, FCOVD, FNORA Massachusetts Society of Optometrists March 2012 What is Photosensitivity • Photosensitivity is a term used to describe an abnormal sensitivity to light • It is also termed photophobia but it is not a fear of light • Bright light and even normal light is experienced as uncomfortable • It is different than photosensitivity from ocular disease • Performance may be impaired in dim illumination • It may lead to disability What is Photosensitivity For patients reporting photosensitivity: • Objective increase in light sensitivity within three weeks of minor head injury • And six months following mild head injury for those with persistent concussion • Less likely to report impairment in the dark (ask about visual ability in the dark) 1 Glare Disability • When a glare source becomes annoying • From scattering of light within the eye • Patient describes being visually disabled in bright light conditions • May come from strong extraneous light sources such as oncoming headlights • Reduction of the contrast of the retinal image • Often due to optical irregularities within the eye such as cataract Functional Photophobia • Described by Ben Lane, OD • Source is non-ocular and rarely accompanied by pain • Often seen with headaches, nausea and dizziness • Waviness or shimmering of surround 2 Visual Stress • Described by Professor Arnold J. Wilkins • Eyestrain, headaches and often seizures provoked by reading • Closely related to photophobia • Can occur despite normal binocular vision • Patients report movement or blurring of print, letters changing size/doubling, nausea or dizziness 3 Causes of Photosensitivity • • • • • • • Cortical hyperexcitability Elevated dark adaptation thresholds Binocular vision disorders Accommodative fatigue Binocular dysfunction Medications Ocular Disease Cortical Hyperexcitability • Proposed by Wilkins • A spread of excitation that causes visual neurons to fire inappropriately • Black and white stripes cause a non-uniform spread of excitation among neighboring pyramidal neurons • Not stopped by normal cortical inhibition • May be a lack of uptake of glutamate • May be suppressed with medications that promote GABAergic transmission 4 Elevated Dark Adaptation Thresholds • Dark Adaptation helps us maintain a constant level of light sensitivity regardless of the level of ambient illumination • Brain injured patients exhibit decreased photosensitivity in the dark (despite hypersensitivity to light in typical room illumination) Elevated Dark Adaptation Thresholds • Mary Jackowski, PhD., OD found elevated dark adaptation thresholds in TBI patients • Those with the most photophobia had the most elevated thresholds • Rod mediated visual sensitivity was impaired. • Patients are impaired in the dark • The reduced rod mediated response may allow for the exaggerated cone response Elevated Dark Adaptation Thresholds • Du, Ciuffreda and Kapoor found more than 50% of brain injured patients with photsensitivity exhibited elevated dark adaptation • An anomalous cortical adaptive response while trying to attenuate light that leads to excessive attentuation 5 Binocular Vision Disorders • • • • Common after brain injury Most often receded convergence Prism vergence testing Sometimes difficult to distinguish from visual stress • Optometric vision therapy is effective for treating binocular vision disorders Binocular Vision Disorders • Pattern sensitivity (Wilkins) is often greater under binocular viewing conditions. • Covering one eye reduced pattern sensitivity • Photosensitive epilepsy – the patient’s response to flicker is reduced while covering one eye 6 Binocular Vision Disorders • Monocular eye closure seen in strabismus • Monocular photophobia threshold higher than binocular threshold • Binocular photophobia threshold lower in those reporting eye closure • Monocular eye closure is a mechanism to reduce photophobia Accommodative Fatigue • +/- 2.00 accommodative testing • Related to binocular dysfunction (in functional photophobia) and dramatically relieved by covering one eye • Low plus lenses effective 7 Visual Field Sensitivity • TBI patients complain of loss of peripheral visual field awareness (and show rod mediated sensitivity loss) • FDT was used to measure visual field sensitivity in the central 30 degrees • All patients complaining of light sensitivity demonstrated loss of sensitivity within the central 30 degrees 8 Visual Field Sensitivity • The most affected patients exhibited constriction with preservation of sensitivity within the central 10 degrees • All patients reported episodes of visual field collapse and dimming of visual field brightness during testing • Symptoms were alleviated with eye closure Associated Conditions • • • • • • Pupil Dilation Dry Eye Medications Eye disease Migraine headache Asthenopia Impact on Daily Life • Recognition that symptoms are real • Affects academic, occupational and recreational demands • Reading discomfort • Pattern glare • Loss of visual function in the dark • Peripheral visual field reduction • Visual distortion 9 Impact on Daily Life • Less likely to be aware of difficulty in dim illumination • Less likely to be aware of visual field constriction while driving • Demonstration of 20 degree VF Impact on Daily Life • Reading may provoke pattern glare that leads to eyestrain, headache and even seizures • Pattern from text can induce peripheral distortions leading to headache and eyestrain • Spacing of characters on the page important • Masking all but one line at a time helpful 10 Optometric Evaluation • • • • • • Detailed history academic, occupational and recreational needs photophobia performance in dim illumination reading driving Optometric Evaluation • Careful assessment of pupil responses – mydriasis, assymetric, alpha-omega pupil • Determination of refractive status – trial frame • Oculomotor status – DEM • Accommodative ability and flexibility • Binocular status – NPC, stamina of control 11 Optometric Evaluation • • • • • Visual field study automated visual field limitation use of kinetic performance field Identify generalized visual field constriction degree of constriction often correlates with severity of symptoms Contrast Sensitivity • Contrast sensitivity • loss of contrast sensitivity for middle to low spatial frequency • magnocelluar system damage • may explain foggy vision and difficulty with daily activities 12 Quantifying Photosensitivity • Stage PP-Zero = no apparent hypersensitivity • Stage PP-1 = Newly experienced, usually short-lived hypersensitivity to extremely bright outdoor sun illuminating a large, bright peripheral field, walls, pavement or other surfaces • Stage PP-2 = Chronic hypersensitivity especially to hazy-bright skies Quantifying Photosensitivity • Stage PP3 = Usually many years of hypersensitivity resulting in great discomfort in supermarkets where the whole ceiling is brightly illuminated • Stage PP4: The final stage of a long chain of decreasing binocular vision skills or a degenerative chain instituted by trauma, characterized by intolerance even to usual relatively low levels of illumination used in home lighting. Quantifying Photosensitivity • Degree of subjective symptoms • present some or all of the time • does patient present wearing dark glasses indoors or ask that room lighting be kept to a dim level 13 Brain Imaging • CT or MRI generally normal and not predictive of visual deficit • SPECT (single photon emission computed tomography) -can reveal physiologic changes in metabolic functioning or cerebral blood flow that typically extends beyond the actual anatomic boundaries -brain hypoperfusion found in >50% of patients who demonstrated chronic post concussion symptoms such as headache -consistent with cortical hyerexcitability. Brain Imaging • Full-field ERG results were unremarkable and not sensitive for patients with mild TBI • Visual evoked cortical potentials (VECP) studies revealed waveform abnormalities indicating visual system deficit • Padula et al. reported reductions in N1-P1 amplitudes of visual evoked potentials 14 Treatment Alternatives • • • • • • • Colored Filters (tints) Plus lenses Prism lenses Corning CPF lenses FL-41 tint Chromagen lenses Colored Overlays Treatment Alternatives • Binasal occlusion • Vision therapy • Syntonic phototherapy • Multiple pairs of eyeglasses • Considerations for indoors/outdoors Colored filters • Tinted lenses worn as eyeglasses or clip-on • Colored overlays (sheets of plastic) placed on top of a page of print while reading. • Cosmetic considerations • If mostly with reading consider overlay • Most experience photophobia during tasks other than reading and will need tint full time 15 16 Determining the Best Color • Subjective responses e.g. overlay testing • blue, green, yellow and rose have all been documented as reducing photophobia and improving reading performance. • The Intuitive Colorimeter illuminates a page of text and allows the hue and saturation of the color to be varied independently at constant brightness • it is used to obtain a color that reduced perceptual distortion • the color is then presented in tinted trial lenses under more natural viewing conditions 17 Determining the Best Color • If a patient prefers a certain colored overlay will they be successful with the same color in a tinted lens? • Tinted lenses to match the luminance of the overlay have been effective • Sometimes the color of the overlay is different than the chosen color of the tinted lens -overlays provide a surface color in the presence of white light - tinted lenses are like changing the color of the lighting Corning Photochromic Filters • Known as CPF lenses • CPF 450-S (yellow), CPF 527-S (orange-amber) and CPF 550-S (orange-red) • CPF 450-S provided the greatest improvement in contrast sensitivity and all of the mild TBI patients tested demonstrated significant improvement in reading rate • CPF 450-S was used for reading and driving and at one year post use continued to provide control of light sensitivity, reduced headache and faster reading speed 18 FL-41 lenses • Rose tint • Kathleen Digre, MD tested patients with photophobia, headaches and blepharospasm • gray lenses also reduced symptoms for patients with blepharospasm but they preferred the FL-41 lenses 19 Chromagen lenses 20 Plus and Prism lenses • Plus treats the underlying accommodative fatigue • Prism and binasal occlusion appear to balance the focal and ambient visual processes • Plus and yoked prism • Plus and BI prism • Plus and binasal occlusion • All may be combined with a tint Vision Therapy • Vision Therapy for visual efficiency • Consideration of techniques to enhance oculomotor, accommodative and binocular function • May take longer than a basic visual efficiency case • Even partial relief is helpful and appreciated Syntonic Phototherapy • The use of colored light delivered through the eyes • Has been used for treating vision conditions for over eighty years • Goal is expansion of constricted visual field and reduction of symptoms 21 Syntonic Phototherapy • 20-minute light treatment , 3-5 days a week, 20 to 40 sessions of treatment • Scientific basis for phototherapy is emerging and may relate to improving mitochondrial energy production and metabolism. For Glare Reduction How to Think about Treatment • • • • Multiple pairs of eyeglasses Considerations for indoors and outdoors Avoid progressive lenses Tinted lenses vs. polarized lenses for outdoors 22 Toolkit for treatment • • • • • • • In-office “trial set” of lenses single vision +0.25 to +1.00 single vision +0.25 to +1.00 with 1BI single vision +0.25 to +1.00 with 2BD Streff wedge to test for binasal occlusion Set of tinted lenses and set of colored overlays Combination of lens holders, flippers, clip-on frames 23 www.brainpowerusa.com/ Pearls • Photophobia persists even after other symptoms have resolved • Discomfort is indoors and outdoors • Often more sensitive to fluorescent lighting • Difficulty in dim illumination • Visual field collapse • Reduced contrast sensitivity 24 Pearls • Consider multiple pairs of lenses • Frequently require lenses for activities at varied working distances • Avoid progressive lenses • Consider multiple visits as patients fatigue easily • Written instruction for use of lenses • Refer for vision therapy and/or phototherapy Uniquely Qualified Optometrists are uniquely qualified to assess, diagnose and treat photosensitivity. Patients properly treated report not only decreased photosensitivity but also improved visual acuity, reading speed and contrast sensitivity. They are report reduced asthenopia and headache. Light Pathways • Nonvisual photoreceptors of the deep brain, pineal gland and retina • Hypothalamus: suprachiasmatic nucleus>pituitary • Pituitary: ACTH to adrenal gland >cortisol/stress hormone • Retina: influences suprachiasmatic nucleus • Pineal: melatonin production 25 Pathways for light-induced activation of non-visual brain areas (A) Light exposure activates melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGC), which are most sensitive to short-wavelength visible light, and conedriven classical ganglion cells (cRGC) of the color vision system, which are most sensitive to mid-wavelength light. (B) Melanopsincontaining ipRGCs project to a range of ‘non-visual’ areas of the brain, including the suprachiasmatic nuclei (SCN), which then project multisynaptically to the pineal gland, as well as to areas that share input from the visual photoreceptor system, such as the lateral geniculate nucleus (LGN), pretectum and superior colliculus (SuC). Through as yet unidentified pathways, light stimulates the ascending arousal system and eventually the cortex to enhance alertness and cognition. INL, inner nuclear layer; ONL, outer nuclear layer; RPE, retinal pigment epithelium. (Adapted from Saper, C.B., Scammell, T.E., and Lu, J. (2005). Hypothalamic regulation of sleep and circadian rhythms. Nature 437, 1257–1263. 26 Illustration of ocular photic transmission pathway As light enters the eyes, it is absorbed by photopigments in either the rods or cones in the photoreceptive field (PR), which convert it into a voltage signal. The signal triggers a cascade of synaptic activities through activation of secondorder neurons: horizontal cell (HC), bipolar cells (BC), and amacrine cells (AC). The ganglion cells then carry photic input, projecting either to the suprachiasmatic nuclei (SCN) or the lateral geniculate nucleus (LGN). A subset of intrinsically photoresponsive retinal ganglion cells (ipRGCs), expressing melanopsin and cryptochromes, feed the circadian system. 27
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