Transcript Visual Stress Arnold Wilkins University of Essex, UK

Disturbing
vision
Arnold Wilkins
University of Essex, UK
© Debbie Ayles, 2004
A whistle-stop tour



Images in nature have a particular spatial
structure to which we are adapted.
In the modern world images have a
different structure and have become
“stressful”.
This has biological consequences when the
visual cortex is hyperexcitable – a variety
of neurological symptoms, including
headache.
Very uncomfortable stimulus




In nature there are few spatially repetitive
patterns of stripes
We have not evolved to process these
patterns
They are very uncomfortable.
I will now show you a very uncomfortable
image.
!
Very uncomfortable stimulus

Images like this are everywhere

Here are some examples...
Discomfort, illusions
and individual differences

Stripes and other spatially repetitious stimuli
evoke not only discomfort but illusions.

There are individual differences in susceptibility.

The illusions are related to your headaches.

I will now demonstrate this...
Perceptual distortion
•red
•green
•blue
•yellow
•shimmering
•flickering
•shadowy shapes
•blurring
Which did you see?
•red
•green
•blue
•yellow
•shimmering
•flickering
•shadowy shapes
•blurring
Headaches and perceptual distortions are
related.
Headaches
12 or
less
More than 2
2 or less
more
than 12
Links between distortions and headaches





people who see many distortions have more
headaches
they see more distortions on days when they
have a headache
if the headache is on one side of the head the
distortions are asymmetric
people with migraine dislike the pattern
those with aura (warning of headache) see
more distortions on the side of the aura
Wilkins, A.J. Visual Stress Oxford University Press, 1995
fMRI
BOLD Signal Change in V1 (%)
Haemodynamic response
4
3
2
1
0
Non-headache
controls
0.3
1
3
10
Spatial frequency
(cycles/degree)
Huang, J. Cooper, T. G. Satana, B. Kaufman, D. I. Cao, Y. (2003). Visual distortion
associated with hyper visual neuronal activity in migraine. Headache, 43, 664-671.
fMRI
BOLD Signal Change in V1 (%)
Haemodynamic response
4
3
**
Migraine
*
2
Y.
1
0
Non-headache
controls
0.3
1
3
10
Spatial frequency
(cycles/degree)
Huang, J. Cooper, T. G. Satana, B. Kaufman, D. I. Cao, Y. (2003). Visual distortion
associated with hyper visual neuronal activity in migraine. Headache, 43, 664-671.
Individual differences


So the individual differences in
susceptibility to illusions from strong
patterns may reflect cortical
hyperexcitability.
.
Photophobia from hyperexcitability?

Most patients are
photophobic during a
migraine attack.

About 40% of patients with
migraine report visual
triggers of their migraine.

Perhaps flicker and
patterns in the
environment trigger
migraine...
Tints in migraine

Some patients with migraine report tinted
lenses helpful.

They do not all choose the same colour.

Which tint is best?
Intuitive
Colorimeter
Hue
Trial lenses
Saturation
Green
Yellow
Orange
Brightness
Rose
100
transmission (%)
Shines
coloured
light on
text
Rose
Turquoise
Blue
0
400
wavelength (nm)
Purple
700
Wilkins, A.J., Milroy, R., Nimmo-Smith,I.,Wright, A., Tyrrell, R., Holland, K., Martin, J., Bald, J., Yale, S.,
Miles, T., Noakes,T. (1992) Preliminary observations concerning treatment of visual discomfort and
associated perceptual distortion. Ophthalmic and Physiological Optics, 12, 257-263.
Large reduction in activation with precision tint
Huang, J., Zong, X., Wilkins, A., Jenkins, B., Bozoki, A. and Cao, Y. (2011). fMRI
evidence that precision ophthalmic tints reduce cortical hyperactivation in migraine.
Cephalalgia , 31(8), 925-36.
Summary




Some patients with migraine benefit from tinted
lenses
The best tint varies from patient to patient
Patients with migraine have an abnormally large
(fMRI BOLD) and short (NIRS) haemodynamic
response to stressful visual stimuli
Individually selected tints make the response
more normal – decreasing amplitude and
lengthening the response
Clinical trial



What is the effect of tints in clinical
practice?
Small pilot double–masked trial compared
two tints, one that reduced discomfort
from patterns and another tint that
differed in color by a small amount.
Patients did not know which was which.
Pilot double-masked placebo-controlled trial
Control
Lens
proportion when control lenses worn
Days with symptoms
1
12
0.9
0.8
Log odds
p<0.02
0.7
6
0.6
0.5
0.4
0.3
0.2
Precision
Tint
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
proportion when active lenses worn
Wilkins, A.J., Patel, R. Adjamian, R., Evans, B.J.W. (2002). Tinted spectacles and visually
sensitive migraine. Cephalalgia, 22, 711-719.
Conclusion




Environmental stimuli, including text, can be
stressful, giving headaches.
The individual differences in susceptibility may be
associated with an abnormal excitability of the
brain.
This may be why precision tints can sometimes
improve reading speed and reduce discomfort.
Precision tints reduce days with symptoms in a
small study- we now wish to extend this study to
a trial in general practice.
Thanks to:
Peter Allen
John Findlay
Ian Nimmo-Smith
Liz Ashby
Nicola Grayson
Tim Noakes
Debbie Ayles
Sarah Haigh
Duncan Nulty
John Bald
Graham Harding
Ragini Patel
Tom Beare
Gemma Hardy
Charlotte Peach
Alex Boyd
Jie Huang
Nirmal Sihra
Anne Busby
Laura Hughes
Anita Simmers
Edward Chronicle
Stephanie Jainta
Jennifer Smith
Roanna Cleave
Rebecca Jeanes
Lianne Smith
Chris Cooper
Anita Lightstone
Lynne Speedwell
Louise Coutts
Amanda Ludlow
Nicola Stevenson
Colleen Darby
Ann Maclachlan
Lynette Taylor
John Duffy
Judith Martin
Ruth Tyrrell
Frank Eperjesi
Hazel McWhinnie
Louise Wilson
Bruce Evans
Brian Meldrum
Wolfgang Jaschinski
Marylyn Evans
Louise Mell
Ben Wright
Dominic Fernandez
Catherine Neary
Sheila Yale
Further information
Peter Bex
Samantha Harper
David Pointon
www.essex.ac.uk/psychology/overlays/publications2.htm
Colin Binnie
Pamela Heaton
Lorna Scott