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Horse Facts and Tips
Medical Index
First Posted: Oct 13, 2012
Oct 13, 2012

Eye Exams in Horses

by Debora Johnson

When it comes to the horse's eyes I have been told all my life that time is really important. Whether it is true or not--call the vet ASAP! With our horses we always call the vet right away, hopefully we will discover an eye problem within 24 hours. The horses are checked at least twice a day in the morning and in the evening.

My husband and I routinely check each horse for the following:
  • Swelling
  • Squinting
  • Closed eye
  • Drainage
  • Tearing
  • Changes in the pupil
  • Color changes in the eye
  • Cloudy eye
  • Ulcers in the eye
  • Conjunctivitis - The conjunctiva are the membranes that line the inside of the horse's eyelids, and conjunctivitis means that these membranes have become inflamed for some reason. Horses with corneal ulcers will often also have a degree of conjunctivitis. It It is an extremely common condition, especially in mid-to-late summer, when flies play a big part in causing it.
  • Blood in the eye
  • Punctures in the eye or pupil

Simple Diagnostic Tests

Flourescein dye strips - Fluorescein dye is a water soluble dye which is unable to penetrate the lipid containing corneal or conjunctival eipthelium unless there is a break in its integrity. This allows the identification of damage in these structures which otherwise might be difficult to detect. Uses: All cases with signs of corneal disease and/or ocular pain especially ulceration, as part of complete ophthalmologic examination, check patency of naso-lacrimal drainage apparatus.

Seidel's test: The Seidel Test is used to assess the presence of anterior chamber leakage in the cornea. It is used as a screening test for many corneal disorders including corneal post-trauma, corneal perforation and corneal degeneration. The Seidel Test is named after the German Ophthalmologist Erich Seidel (1882-1948). A fluorescein strip containing 10% fluorescein is applied topically to the affected area and is examined with a cobalt blue filter. At this point, the fluorescein appears green in color. Any changes in color or surface of the fluorescence area indicate the presence of corneal leakage. If the fluorescein strip turns pale upon application to the corneal surface, the test is positive for the corneal deformity. The change in the color of the fluorescein strip is due to dilution of fluorescein caused by the aqueous leakage in the cornea.

Rose Bengal stain - To stain the cornea, Rose Bengal and/or Fluorescein strips. Fluorescein strips are more commonly used, and will stain areas where there is loss of epithelium. Rose Bengal will stain areas with devitalized epithelium, as well as reveal where epithelium is lost. Either strip should be held against the conjunctiva, or alternatively, the strip can be wetted with sterile saline and then the solution can be dropped across the eye. As the strip can be somewhat irritating if placed directly on the cornea, direct corneal contact should be avoided. If one suspects decreased tear production, a Schirmer tear test should be performed. A Schirmer tear test strip is folded and applied just inside the lower lid so that it hangs vertically. The wetting of the strip (which has mm markings along its length) by tears can be directly observed and measured for a given time. Both eyes should be compared. Normal horses and ponies tear at least 15mm/60secs. As the name suggests, this rose-colored stain is used to evaluate the eye's tear film integrity.

Corneal scrapings--Sometimes corneal scrapings are taken when ulcers are present. It is bacteria or fungus that is being targeted for treatment.

Intraocular pressure - Although primary glaucoma exists in the horse, the secondary form appears to be most common. Trauma, lens luxation, and particularly uveitis are known causes of secondary glaucoma in the horse. Tono-Pens are often used for the test. Sometimes motor nerve blocks will be used. Ocular ultrasound is also used as an advanced technology for testing for glaucoma in the horse.


Ultrasound of a horse's eye by John Kaufman DVM

Exam Results

After a complete eye examination has been performed on your horse the vet would be able to identify most of the following:
  • Conjunctivitis
  • Uveitis
  • Cataracts
  • Hyphema (blood in the eye)
  • Corneal abscess, necrosis, edema, or ulcers
  • Stromal abscesses
  • Subepithelial infiltrates
  • Immune mediated keratitis
  • Glaucoma
  • Retinal or optic nerve disease
  • Parasites

For More Information:

Ophthalmic Exam/University of PA/Veterinary What's in an Eye Exam?
Eye Diseases Associated With Specific Horse Breeds
Equine Opthomology/49th Ocala Equine conference
Equine Recurrent Uveitis
Equine Parasites
Horse Vision
Neurological Problem Signs in Horses

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