Download Literally! - Ophthalmoscopy

LITERALLY!
with Debra Gates BVSc.
Most clinics have a direct
ophthalmoscope sitting on the bench,
but I suspect that many of us are not
confident in its use.
Most ophthalmoscopes offer a variety
of light beams, but for vets the large
diameter beam is used routinely as
long as the pupil is adequately dilated.
Dark adaptation will help with dilation but the best product to
use is 1% Tropicamide which is sold by Alcon as Mydriacyl. It
takes effect after 20 minutes and lasts 4-5 hours. This is much
better than atropine which can leave the pupil dilated for 5-7
days in dogs and horses.
The little numbers on the scope can be a bit of a mystery,
but relate to the lenses used to focus in different parts of the
eye, and accommodate for any optical correction the user
may need. Before starting have your patient firmly restrained
with a steadying hand under the angle of the jaw and be as
systematic as possible in your examination. Begin with the
ophthalmoscope on a 0 or +1 diopter setting at arm’s length
from the patient as it is easier to pick up lens opacities from
there. Gradually move in until you are as close to the eye as
you can comfortably get and change to -2 (red 2). This setting
will suffice for examination of the disc and fundus in most
situations. The fundus will be real and upright and magnified
14x. The bad news is that your field of view will be very narrow
and you will have to work systematically to examine the entire
eye. Start at the disc and then divide the fundus into quadrants,
covering each in turn. The patient’s eye movements will both
help and hinder your quest. Like most things it all gets easier
with practice. Try to keep both of your eyes open while you
perform the examination as it will reduce fatigue. Use your
right eye to observe on the left side and vice versa.
Indirect ophthalmoscopy utilises a 20 diopter lens and an
independent light source to form an inverted and reversed view
of the fundus. Your eye, the light-source, lens and patient’s
pupil should as far as possible lie in the same axis. Therefore
the light is held beside your temple or in front of your nose.
Alternately you can use a head-mounted light and keep both
hands free. The critical thing though is to have the plane of the
indirect lens perpendicular to the lens of the eye.
Indirect ophthalmoscopy is undervalued, as the wideangle view is easier to interpret and gives a great deal of
information rapidly, but because of lesser magnification (2-4x)
it won’t provide as much detail as is gleaned through a direct
technique.
There are some excellent texts available on ophthalmology, but
nothing beats getting in there and learning from doing.