Measuring the IOP –intraocular pressure The normal IOP is 10 to 25 mmHg. Tonometry is the technique used to measure the IOP. Glaucoma can be defined

Measuring the IOP –intraocular pressure

The normal IOP is 10 to 25 mmHg. Tonometry is the technique used to measure the IOP. Glaucoma can be defined as a raised intraocular pressure that affects the health of the optic nerve. Most dogs presenting with glaucoma have an IOP greater than 40 mmHg. It is very important that glaucoma is recognized very quickly to give the eye any chance of saving its vision.

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When you should measure the IOP? You should measure the IOP...

1. When you suspect glaucoma - the cardinal signs of glaucoma are a red eye, a blue eye and a mid-dilated non responsive pupil.
2. In any red eye. Uveitis and hyphaema can lead to glaucoma. Regular re-examination and tonometry allows you to chart the IOP, and diagnose glaucoma before vision is lost. Remember that you can use the IOP as a guide to your uveitis treatment. If the IOP was initially low eg 5 mmg, and has increased to 15 mmHg then your uveitis has been controlled. If the IOP in the uveitis treated eye goes from low to above 20 mmHg, secondary glaucoma is developing.

3. In all blue eyes. It could be glaucoma, or it could be an anterior lens luxation which usually ends up with secondary glaucoma, or uveitis in which the IOP should always be measured.
4. In any eye disease in pure bred dogs that may be prone to glaucoma. Check the breed predisposition list.Contact Animal Eye Care if you would like a list of glaucoma prone breeds.
5. Serial IOP measurements in dogs do not seem to have any benefit in predicting glaucoma in dogs. However serial IOP measurements in cats has been shown to help detect glaucoma in cats before it causes clinical signs and blindness.

How to measure the IOP.

The IOP is measured with a tonometer. There are 3 basic types of tonometers 1) Indentation—the Schiotz Tonometer and 2) Applanation tonometry—the Tonopen and Tonpen Avia and 3) Rebound—The TonoVet.

With each type of tonometry there can be potential errors, and as always the IOP readings should be correlated to the clinical signs. It is important to have a standardised technique to reduce measurement errors.

Animal Eye Care uses the Tonopen and the Tonopen Avia to measure the IOP. We are happy to provide advice on what tonometer to buy and how to measure the IOP.

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