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Eye
Testing
What happens
when I go for an Eye test?
Eye
examinations at Perfect
Vision usually last about half an
hour, during your
examination your
optometrist may
perform one or more of the following tests.
The test is non invasive and easy to do
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Retinoscopy
This
is one of the first tests to be performed in
an eye examination
and it will give your optometrist an idea of
what kind of prescription you may need. In a
darkened room, you’ll be asked to stare at a
target, such as a large letter E. The
optometrist will shine a light into your
eyes and will look at the way your eyes
reflect light when different lenses are
passed in front of them. |
Refraction
This test fine-tunes the prescription estimated by
the retinoscopy. An instrument called a phoropter
will be put in front of your eyes and you will be
asked which of each choice of two lenses looks the
clearer. Based on your answers, the optometrist will
be able to determine which exact prescription is
best for you. Refraction tells you how long-sighted,
short-sighted, astigmatic or presbyopic you are.
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Visual
acuity
The visual acuity test is the one most
people think of when they think of an eye
exam. You will be shown an eye chart and
asked to say what’s on it. Adults are
usually shown letters of the alphabet, while
young children are often shown pictures.
Amsler grid
The Amsler grid is a pattern of lines in a
square check formation, with a spot in the
middle. While staring at the dot, you may
notice variations in the regularity of the
lines. This tests your central vision and
can be used to detect the onset of
age-related macular degeneration.
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Visual
field
This test consists of lights flashing in the
periphery of your vision while you stare at
a light in the centre of your field of view.
Also known as the perimetry test, it
measures your peripheral vision and can be
used to detect the onset of open-angle
glaucoma.
Cover test
For this test, your eyes will be alternately
covered while you focus on a distant object.
By looking at how much each eye has to move
to focus on the object, the optometrist can
detect strabismus (eye turn), which can lead
to amblyopia (lazy eye), poor depth
perception and other conditions.
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Slit lamp
test
The slit lamp examination is like looking
into your eyes
through a powerful microscope.
The instrument
used is called a biomicroscope and it allows
your optometrist to get a close look at the
internal structures of the eye.
The eyelids, cornea, iris, conjunctiva,
retina, optic nerve and macula are among the
things that can be seen with a biomicroscope,
and cataracts, macular degeneration,
diabetic eye disease and corneal ulcers can
all be detected using this test.
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Tonometry
This measures the pressure inside your eye,
which is also called intraocular pressure.
It is used to test for glaucoma and often
involves a non-contact tonometer, also known
as the "puff of air" test.
This involves
having a puff of air directed at your eye.
The machine will calculate your intraocular
pressure on the basis of your eye’s
resistance to the air. It is completely
painless. For the other type of glaucoma
test, your eye needs to be numbed and the
optometrist will do this by giving you a
yellow eyedrop. Once the drop has taken
effect, you’ll be asked to stare into the
slit lamp while the optometrist touches you
on the front of each eye with a bright blue
glowing instrument. This may not sound nice,
but it is
painless.
Dilation
The pupil (the black spot in the middle of
your eye) is effectively the hole through
which your optometrist looks into your eye.
The larger the pupil, the bigger the
"window" is to look through. Because of
this, you may be required to take some
dilating drops,
these usually take a few
minutes to start working and will probably
make your eyes more sensitive to light. It
is advisable to take along a pair of
sunglasses to your exam as this sensitivity
can last for several hours after you have
left the surgery.
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Colour vision testing
The usual test for colour blindness
involves looking at numbers formed
of dots against a background of dots
of a different colour. These
pictures are called Ishihara plates.
People with normal colour vision
will see the number as it is meant
to be, while people with colour
vision problems may see a different
number (for example a 3 instead of
an 8), or even no number at all.
These are the most common tests
performed in an eye exam, but there
are others and you shouldn’t be
alarmed if tests are performed on
you that haven’t been mentioned
here. It is also important that
you’re honest in the answers you
give to any questions the
optometrist asks; concealing or even
just playing down problems may make
it more difficult to make a proper
diagnosis.
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