The main clinical focus of the Vision Science Centre is
Ophthalmic Electrodiagnosis. These are objective tests of the
function, structure and performance of the visual system.
The tests are painless. Sensors are attached to the skin at the
back of the head or around the eyes. These then pick up tiny
electrical signals which naturally occur when the patient's visual
system is stimulated, either by patterns on a TV screen or by a
The following tests are routinely carried out. Each test takes
about 30 minutes but not all patients have all tests performed. It
depends on the clinical question being asked. We also spend up to
half an hour on preliminary tests where we measure such things as
visual acuity and colour vision.
Visual Evoked Potentials (VEPs)
This is a way of analysing brain waves which occur when
the patient looks at a moving pattern on a screen or at a flashing
light. By correlating the brain responses with the stimulus we can
check the function of the optic nerves and the seeing part of the
brain. The sensors are attached to the scalp using a harmless and
easily-removed adhesive paste.
Flash Electroretinograms (ERGs)
By recording from sensors placed close to the eye we can
analyse the electrical signals produced by the eye in response to
flashing lights. Part of this test is carried out in the light, and
part of it follows a period of 15-20 minutes adaptation to
darkness. Thus we are able to analyse the overall function of the
retina's light-sensitive layer (the photoreceptors, or rods and
cones). Two sensors are taped to the temples. We then lay a fine
thread along the lower eyelid so that it rests against the eye or
(with younger patients) attach a small sensor to the skin of the
lower eyelid. This test is routinely conducted with dilated pupils,
for which drops are put in the eye. Because these drops tend to
cause some temporary blurring as well as enlarging the pupils, we
recommend that patients do not drive themselves to their
Pattern Electroretinograms (pERGs)
Using the same sensors as the flash ERG, but a patterned
stimulus, we can further analyse the function of the optic nerve
and the macula (the very sensitive central portion of the
This is another test of retinal function and is used to
assess the integrity of the retinal pigment epithelium (RPE). This
is the layer of the retina which nourishes the light-sensitive
cells. Sensors are placed on the skin either side of each eye and
the patient is asked to make a series of guided eye-movements at
intervals over a period of about half an hour. Half the time is
spent in darkness, and half in bright light.
We try to tailor the tests to the ability of the patient,
and routinely just do VEPs and flash ERGs with younger children.
They can sit on a parent's lap throughout the procedure. During the
test we can play videos or music which encourages the patient to
look at the test stimulus.
Children can bring their own video tapes, DVDs or CDs, and
it is also a good idea to bring along a drink, a snack and a spare
nappy (if used). A favourite toy (preferably small and noisy) can
help us encourage the child to look at the stimulus. We have baby
changing facilities in the unit.
A fun and informative video that will inform children of what
happens can be found by
Professor Neil Parry
The Vision Science Centre operates as an outpatient department
and is open between the hours of 09.00am to 5.00pm. Admission is by
referral from a Consultant Ophthalmologist.
Tel: 0161 276 5561
Manchester Royal Eye Hospital
Central Manchester University Hospitals NHS Foundation Trust
Click here for directions to the Hospital