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Vision and dyslexia
Prof Bruce EvansBSc (Hons) PhD FCOptom DipCLP DipOrth FAAO FBCLA
Director of Research Institute of Optometry
Visiting Professor City University
Private practice Brentwood, Essex
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Which eyecare practitioner?
Dispensing Opticians (5,100 in UK)
Dispense spectacles
Some also fit contact lenses
Orthoptists (1,000 in UK)
Mainly involved in orthoptics
(binocular vision)
Some also do vision screening
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Which eyecare practitioner?
Ophthalmologists
In UK: 900 consultants; 1,400 in training
Optometrists (10,400 in UK)
Detect eye diseases
Detect & treat refractive & orthoptic problems
Prescribe glasses & contact lenses
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The term dyslexia
The word dyslexia means many different things to different people (Hartstein, 1968)
a specific difficulty with reading and spelling
“an unexpected problem in learning to read and spell in people who seem otherwise capable and intelligent”
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What causes dyslexia?
mainly a problem of making
words into sounds (phonology)
vision is a factor in some cases
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Who diagnoses dyslexia?
educational psychologist
teachers may recognise signs
optometrists & orthoptists only
look at visual factors
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Common visual
problems in dyslexia
Meares-Irlen Syndrome
poor binocular co-ordination
focussing (accommodation)
problems
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Normal eye examination
eye health
refraction
basic binocular co-ordination
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Special investigation of
vision & learning
12 extra tests of binocular coordination
4 extra tests of focussing skills
assessment of Meares-Irlen Syndrome
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PLAN
INTRODUCTION
CONVENTIONAL OPTOMETRIC CORRELATES
MAGNO (TRANSIENT) VISUAL DEFICIT
BEHAVIORAL OPTOMETRY
MEARES-IRLEN SYNDROME& VISUAL STRESS
CONCLUSIONS
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Optometric correlates of reading difficulties:
binocular instability
SYMPTOMS: blur, double vision, visual perceptual
distortions, eye strain & headaches
SIGNS: low fusional reserves,
unstable heterophoria
Evans et al. (1994) Ophthal. Physiol. Opt. 14 , 5-19.
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Optometric correlates of reading difficulties:
binocular instability
SYMPTOMS: blur, double vision, visual perceptual
distortions, eye strain & headaches
SIGNS: low fusional reserves,
unstable heterophoria
TREATMENT: fusional reserve exercises
refractive correction
Evans et al. (1994) Ophthal. Physiol. Opt. 14 , 5-19.
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Ocular accommodation
crystalline lens
in relaxed
state as in
distance vision
crystalline lens
in accommodated
state as in
near vision
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Optometric correlates of dyslexia:
accommodative insufficiency
SYMPTOMS: blur, eye strain & headaches
SIGNS: low amplitude of accommodation,
high accommodative lag
TREATMENT: accommodative exercises (if appropriate)
Evans et al. (1994) Ophthal. Physiol. Opt. 14 , 5-19.
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PLAN
INTRODUCTION
CONVENTIONAL OPTOMETRIC CORRELATES
MAGNO (TRANSIENT) VISUAL DEFICIT
THE DUNLOP TEST & BEHAVIORAL OPTOMETRY
MEARES-IRLEN SYNDROME& VISUAL STRESS
CONCLUSIONS
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Behavioral optometry
As many therapies as there
are practitioners
“no randomised controlled
trials” (Jennings, 2000)
“a large majority of
behavioral management
therapies are not evidence-
based” (Barrett, 2008)Voltaire: “Practical therapeutics is the art of
keeping the patient entertained until nature effects
a cure”
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“Tracking” & dyslexia
Saccades are not unique to reading
Most studies have not found a saccadic eye movement deficit in dyslexia
Dyslexia influences saccades: “search for meaning”
ADD influences saccades
Treatments based on training saccadic or pursuit eye movements are controversial
The DDAT has not been validated by masked controlled trials (PubMed search 15-Oct-06)
“Reynolds et al. (2003) provides no evidence that DDAT is an effective form of treatment” Snowling & Hulme (2003)
PubMed search (15-Oct-06) reveals no published research on BrightStar system
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PLAN
INTRODUCTION
CONVENTIONAL OPTOMETRIC CORRELATES
MAGNO (TRANSIENT) VISUAL DEFICIT
MEARES-IRLEN SYNDROME & VISUAL STRESS
CONCLUSIONS
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Meares-Irlen Syndrome = symptoms + benefit from colour
a.k.a. Scotopic Sensitivity syndrome, Irlen syndrome, visual stress
Meares-Irlen Syndrome =
a.k.a. Scotopic Sensitivity syndrome, Irlen syndrome, visual stress
Meares-Irlen Syndrome / Visual Stress (MISViS)
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The Intuitive Colorimeter
Wilkins et al. (1992) Figures courtesy of Prof. Arnold Wilkins
0.60.50.40.30.20.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
v'
u'
•hue, saturation, luminance varied independently
•eyes remain colour-adapted
•no coloured surfaces visible
•large gamut
•colour change continuous
hue
saturation
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Precision Tinted Lenses (PTL)
Wilkins et al. (1992) Figures courtesy of Prof. Arnold Wilkins
Rose
Rose
Yellow
Blue
Turquoise
Green Orange
Purple
400 700wavelength (nm)
transmission (%)
100
0
7 dyes: 25 levels of deposition
Rose
Yellow
Orange
Green
Turquoise
BluePurple
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Intuitive Overlays
Wilkins (1993) Figures courtesy of Prof. Arnold Wilkins
Aqua
Bl ue
Mint
Li me Or ange
Rose
Purpl e
wavelength (nm)400 700
100
0
refl
ecta
nce(%)
Pink
Yellow
GreyGrey
NOTE: OVERLAY COLOUR DIFFERS FROM LENS COLOUR
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Assessing optometric interventions
Wilkins Rate of Reading Test
Wilkins et al. (1996) Ophthal. Physiol. Opt. 16, 491-497
come see the play look up is cat not my and dog for you to
the cat up dog and is play come you see for not to look my
you for the and not see my play come is look dog cat to up
dog to you and play cat up is my not come for the look see
play come see cat not look dog is my up the for to and you
to not cat for look is my and up come play you see the dog
my play see to for you is the look up cat not dog come and
look to for my come play the dog see you not cat up and is
up come look for the not dog cat you to see is and my play
is you dog for not cat my look come and up to play see the
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Key research on Meares-Irlen Syndrome
PTL alleviate symptoms when reading
Wilkins, Evans, Busby et al. (1994)
Overlays improve speed of reading
Bouldoukian, Wilkins, Evans (2002)
PTL improve conventional measures
of reading Robinson & Foreman (2000)
The benefit from PTL is not explained
by ocular motor factorsEvans, Wilkins, Busby et al. (1995)
The benefit from PTL is linked to
pattern glare Evans, Wilkins, Brown et al. (1996)
.
N=6N=6
N=19N=19
N=11N=11
% when control glasses worn
% when active glasses worn.
N=6N=6
N=19N=19
N=11N=11
% when control glasses worn
% when active glasses worn
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Key research on Meares-Irlen Syndrome (cont)
>80% of people prescribed PTL are still using after one year Evans, Patel, Wilkins et al. (1999)
Overlay colour cannot be used to predict lens colourLightstone, Lightstone, Wilkins (1999)
Visual Stress is nearly as common in adults as children Joseph & Evans (1999)
Visual Stress is about 2-3x more common in dyslexic children than non-dyslexic Kriss & Evans (2005)
86889092949698100102
Read
ing
rate
(w
pm
)
Chosen
overlay
Lenses
matching
colorimeter
No
overlay
or lens
Lenses matching
chosen overlay
86889092949698100102
Read
ing
rate
(w
pm
)
Chosen
overlay
Lenses
matching
colorimeter
No
overlay
or lens
Lenses matching
chosen overlay
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SEQUENTIAL MANAGEMENT PLAN: educator with overlays
TEST WITH INTUITIVE OVERLAYSnegative
monitor
positive
IS THERE A SIGNIFICANT BENEFIT?
yesno
monitor
continued
ARE EYES HEALTHY?
yes
norefer
REFER TO OPTOMETRIST WITH COLORIMETER
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continued
PRECISION TINTS
INTUITIVE COLORIMETRY
positive
negativemonitor
optometric
correctionIS THERE A SIGNIFICANT REFRACTIVE ERROR?
yes
no
IS THERE A SIGNIFICANT ORTHOPTIC ANOMALY?yes
no
optometric
correction/
treatment
YEARLY CHECKS
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Which systems are validated by RCTs?
Validated
Wilkins/MRC Intuitive Colorimeter
Irlen
? Chromagen
Not validated
Photosyntonics
Orthoscopics & optopraxometer
Tintavision
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Comparison of systems
MRC / Wi lk ins I r len Chromagen
Screen ing Over lays o r PC Over lays None Tes t ing : ab i l i t y to f i nd op t ima l t i n t
Ve ry l a rge range o f co lours
Very la rge range o f co lou rs
9 co lours
Va l ida t ion W i lk ins Ra te o f Read ing Tes t
IDPS W i lk ins Ra te o f Read ing Tes t
Es tab l i shed 1993 1983 c . 1997 fo r dys lex ia
Des ign m in im ises metamer i sm
Yes Probab ly no t Probab ly no t
Ava i lab i l i t y o f con tac t l enses
Yes Yes Yes
Prac t i sed by eyecare p ro fess iona ls
Yes No Yes
Research Many papers , 1 D-M RCT
Many papers , 1 D-M RCT
Two papers , (1 ?D-M RCT)
Unproven techniques: Photosyntonics, Tintavision, Optopraxometer & Orthoscopics
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Who needs referral to a visual stress clinic?
Academic underachievement or difficulties with text (now or in the past)
Visual perceptual distortions when viewing textText moving, blurring, doubling, and seeing patterns on the page
Headaches (including migraine) associated with Visual tasks (e.g., text)
Flickering or fluorescent lighting
School / HE establishment
Offices
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For prescribers of precision tinted lenses
who sign up to a code of conduct about:
relevant CET - 10 hrs in last 5 yrs
Equipment - for BV & PTL
Evidence-based practice
List will be publicised to teachers,
educational psychologists, parents
www.s4clp.org
Society for Coloured lens Prescribers
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Conclusions
Certain visual problems are particularly common in people with reading difficulties
Meares-Irlen Syndrome, binocular instability, accommodative insufficiency
All these problems can cause similar symptoms
Eyestrain, headaches, visual perceptual distortions
People with reading difficulties or these symptoms should be referred to interested eyecare practitioners