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Wrangling on the Range #146

A Look at the horse's Eye


From "Horse Canada" - May/June 2005

Until the Vet Arrives

by Nicole Kitchener

Any condition affecting the eye requires veterinary examination.
Do not wait to see if the problem will clear. Eye conditions,
even if they are left for a couple of days, can lead to serious
complications, including blindness or loss of an eye.
Call your veterinarian if your horse exhibits any of the

* Swollen eyelids
* Tearing or other discharge - watery or yellowish 
* Squinting, blinking 
* Cloudiness of the cornea 
* Obvious cuts, contusions to the lids 
* Scratches or marks on the cornea itself
* Sensitivity to the sun or other bright light
* Bloodshot appearance 
* Presence of heat
* Obvious discomfort such as rubbing the eye
* Bumping into objects, unexplained poor performance, increased
* Sign of tumours

What to do until the veterinarian comes:

l. Restrain the horse.
2. Examine the eye and surrounding area for injury.
3. Place your thumb tip on the lower eyelid and index finger on
the upper lid. With gentle pressure carefully part the eyelids by
separating your thumb and finger. Check for dirt or material
under the lower eyelid.
4. If you see foreign matter, flush the eye with a saline
solution or commercial eye-wash product.
5. Place the horse in a dark, quiet stall, preferably with no
bedding or hay to prevent dust from entering the eye.
6. Apply a moist, cold compress to the eye.
7. Stay with the horse to prevent him from rubbing his eye and
potentially causing further damage.
8. Do not administer medications unless advised by your
veterinarian. Their use may make an eye condition much worse.

When the veterinarian arrives he/she will ask you:

1. What symptoms you have noticed, when they first appeared and
their progression.
2. Whether the horse has been in pain and, if so, is the pain
intermittent or constant?
3. About the horse's general health and any history of eye
4. About the horse's environment? Has it changed recently?

The veterinarian will then do an exam, which may involve:

1. Examination of the eye, eyelids and head, for obvious problems
such as signs of trauma, discharge, squinting, eye movement, etc.
2. Testing the horse's reflexes: a sudden hand movement toward
the eye to test vision; squinting response to bright light
directed in the eye; touching the eyelids to determine blink
3. Investigation of the internal structures of the eye (i.e.
iris, pupil and lens), using an ophthalmoscope.
4. If the condition is painful, sedation, nerve blocks or
administer a local anaesthetic to relieve the horse's discomfort
and facilitate the examination.
5. Performing a Schirmer tear test to determine if the horse is
producing enough tears or too many. A test strip is inserted
under the lower eyelid and measured after one minute for
saturation level.
6. Application of stains to the eyeball to determine whether
ulcers are present or if tear film is abnormal.
7. Taking a culture of the cornea.
8. Depending on the condition, prescribing medications for you to
administer or advising transportation of the patient to an equine
hospital or clinic for further evaluation or surgery.

Parts of the Eye

Sclera - Thick outer layer of eyeball. Known as the "white" of
the eye. Provides shape to the eyeball. Filled with vitreous
humour, a jelly-like liquid.
Cornea - Thick, transparent front surface of eye. Allows light
Chorid - Thin membrane, which provides nourishment to the retina.
Ciliary Body - Pigmented thickening of the sclera's inner
Iris - Pigmented muscular tissue. Gives eye its colour. Dilates
and contracts to regulate the amount of light entering the eye
Pupil - Oval-shaped opening in centre of iris. Controls amount of
light entering eye.
Retina - Transmits light information via optic nerve to brain.
Optic Nerve - Pathway running from back of eye, through sclera to
Lens - Transparent curved body. Focuses images onto the retina
Comprised of outer elastic membrane surrounding layers of clear
Upper and Lower Eyelids - Protect and support eye.
Eyelashes - Filter debris and act as sensors.
Third Eyelid - Thin membrane that provides protection and
lubrication for cornea. Originates from inside corner of eye
Conjunctiva (below) - Moist, pink tissue on inner side of

Eye condition and disorders addition to acute injuries of the
eyelids or the eye itself, such as insect stings, trauma,
bruising and lacerations and tearing, there are a number of
serious conditions (some of which also occur as a result of
injury) that require immediate veterinary attention.

Cataracts are diseased lenses caused by injury, infection,
nutritional deficiencies, and hereditary factors. They appear
opaque and are progressive in nature, resulting in gradual loss
of sight. Surgical treatment is necessary.

Corneal ulcers, are quite common, look like a cloudy spot on the
eye, and are usually the result of an injury or trauma to the
cornea. Ulcers can be painful and cause squinting, tearing,
discharge and redness, if treated promptly with the appropriate
medications, most ulcers are curable, however, if fast action is
not taken, bacterial or fungal infections can set in, causing
what is called a "melting" ulcer, which can result in permanent
damage within hours.

Conjunctivitis, or inflammation of the conjuctiva, is usually
caused by foreign matter (i.e. dust, dirt or vegetation) trapped
under the eyelids. Flushing the eye with a saline solution may
clear the problem, however, veterinary examination should follow,
as corneal scratches and ulcers may be present but unnoticeable.
It is best to leave removal of the matter to a veterinarian.
Sometimes, objects puncture an eyelid or the eye, in which case
stitching or surgery may necessary.

Tear duct obstruction results in tears running down the face. A
veterinarian can usually flush out the duct but, sometimes,
damage is permanent.

Tumours are not uncommon. There are three main types of tumours
affecting the equine eye: sarcoids, carcinomas and melanomas.
They may start out as a small bump or mass and can grow quite
large. They should be watched carefully and measured regularly
for growth. Tumours can be treated with freezing, burning,
surgery, chemotherapy, immune therapy and lasers.

Recurrent uveitis (moon blindness or periodic opthalmia) is
stubborn, painful and is the leading cause of blindness in
horses. The condition is an inflammation of the uvea, the middle
layer of the eye, consisting of the iris, the ciliary body and
the choroid. It often recurs in one or both eyes, with each
subsequent return of the condition damaging the eye further until
blindness results. Uveitis remains a mysterious condition, but it
is believed there are different causes including, allergy,
trauma, infection and the bacteria leptospirosis. During attacks,
the horse is usually administered antiinflammatories and
pain-killers to relieve discomfort.

Please see the July/August issue for more information on moon

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