Using Tonometry To Diagnose Eye Problems In Horses
Intraocular pressure (IOP) is greater in horses than in any other land animal
. Tonometry enables veterinarians to measure the interocular pressure of the horses eye. It is essential to keep the head raised during this procedure because IOP pressure increases 87% when the head is lowered. See veterinary tonometry.
A number of clinical studies have documented average IOP readings in horses. The natural mean IOP reading varies from 15 to 30 mm Hg.
Equine Recurrent Uveitis (ERU) and Glaucoma are both diseases related to abnormal IOP pressure. High pressure causes Glaucoma and low pressure causes ERU. ERU is a frequent eye problem for horses and can eventually result in blindness. Tonometry is key to diagnosing both of these conditions.
Secondary glaucoma is also a complication of ERU. Secondary glaucoma can be extremely painful and often leads to blindness. This condition sometimes results in enucleation or surgical removal of the eye.
Glaucoma is difficult to diagnose in horses because they are able to maintain a clear cornea, even with high intraocular pressure. Glaucoma is often characterized as a "silent thief" of human vision because it is painless. It seems to take a similar course with horses.
The following equine conditions indicate tonometry: a red or painful eye, orbital trauma, corneal edema, a lens luxation or a history of glaucoma in the opposite eye. Tonometry also pays an important role in monitoring the treatment of these conditions.
Precise and verifiable equine IOP readings are provided by Applanation tonometry, and use of this technology is increasing in veterinary practice.
Applanation tonometers have several advantages over the Schiotz tonometer. They are highly accurate, their readings are less affected by corneal disease, they can be used to measure intraocular pressure in vertically as well as horizontally positioned corneas, and are very easy to use, making them the instrument of choice for measuring intraocular pressure in domestic animals. For more information see tonometer comparison.