 |
Dry Eye
|
|
|
 |
The quality of the tear film
is assessed using this instrument. The time taken for the target's
reflection from the layer of tears to break down is timed. (You
can peek through the instrument yourself lower on this page!)
Why we need tears
The cornea is the clear window at the front of the eye. The layer of tears,
wetting the front surface of the cornea exists not just to overflow when
you cry (!) but has a number of important roles to play.
For instance, the corneal tissue needs a good supply of oxygen to keep its
transparency, getting most of this from the oxygen dissolved in the tear
film.
Tears wash away any dust particles or chemical vapours, which could be harmful
to that delicate front surface. The tears that wash across the eye are draining
away down two tear ducts, drainage holes at the inner corner of each eyelid.
And of course the tear film acts as a lubricant to allow the eye to move
freely and comfortably behind the lids.
Dry eyes and the tear film
The tear film itself is more complex than you might think, having three
layers - inner and outer layers are oily with a watery layer
forming the 'filling of the sandwich '. The oily inner layer
helps to keep the tears in contact with the cornea and the
oily outer layer traps the watery layer, which has the important
task to carrying the oxygen.
If any of those layers are not intact it can very quickly
give rise to extreme discomfort. Imagine a reduced outer layer
- with nothing to hold the watery layer intact it will start
to evaporate. The eyes will quickly begin to feel sore, itchy,
gritty, or downright painful. All of these sensations trigger
more watering to try to counteract the grittiness. It is often
a surprise to people to find they have clinically dry eyes
when they know that their eyes often water profusely.
 |
This image demonstrates the
reflection seen by the instrument Place your cursor
over the image to see how the tear film breaks up over
time.
A healthy tear film takes over ten seconds from a blink
to begin to break down - this reduces to three seconds
or less in a dry eye. |
Those with arthritis frequently experience the discomfort
of dry eyes. The usual treatment is to use 'artificial tears'
which can be bought over the counter without a prescription,
and used as often as necessary to relieve the soreness. Sufferers
should be sure to get plenty of 'essential amino acids' in
their diet - these are found in oily fish. Some people have
noticed an improvement by taking Evening Primrose Oil capsules
on a regular basis, which can also reduce the pain from arthritic
joints. Zinc tablets have also proved helpful, although you
have to be careful not to take too much zinc - generally a
course lasting a month will sufficient to bring that trace
element in the body to the level it should be.
Dry eye never really goes away completely, so it is likely
that you will have to keep using the lubricating eye drops
on a regular basis.
Dry eye from reduced tears volume
There is one final type of dry eye where the problem is due to a reduced
quantity of tears being produced. To help the tears remain in contact
with the eye it may be suggested that you are fitted with punctum plugs,
which 'cork up' at least one of the tear ducts in each eye to prevent
the tears running away too quickly.
| |
|
|
 |
