Photosensitivity What is Photosensitivity Dr. Cathy Stern, OD, FCSO, FCOVD, FNORA

Transcription

Photosensitivity What is Photosensitivity Dr. Cathy Stern, OD, FCSO, FCOVD, FNORA
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)
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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
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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
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Causes of Photosensitivity
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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
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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
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Binocular Vision Disorders
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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
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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
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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
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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
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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
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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
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Optometric Evaluation
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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
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Optometric Evaluation
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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
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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
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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
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Treatment Alternatives
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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
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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
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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
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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
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Chromagen lenses
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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
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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
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Multiple pairs of eyeglasses
Considerations for indoors and outdoors
Avoid progressive lenses
Tinted lenses vs. polarized lenses for outdoors
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Toolkit for treatment
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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
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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
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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
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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.
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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.
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