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Advances in tonometry in companion animals
  1. James Oliver, BVSc, CertVOphthal, DipECVO, MRCVS
  1. Vets Now Referrals, 2 Esher Road, Hersham, Surrey KT12 4JY, UK
  1. e-mail: james.oliver{at}

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THE measurement of intraocular pressure (IOP) is an important part of the complete ophthalmic examination and is particularly applicable in the diagnosis and management of uveitis and glaucoma. The normal range of IOP is fairly well conserved among species; it generally ranges between 10 and 25 mmHg and the difference between normal fellow eyes should be no more than 5 mmHg. IOP is influenced by numerous factors other than ocular pathology including age, sex, time of day, season and restraint. Restraint is particularly important when measuring IOP as head and body position, as well as eyelid and jugular vein manipulation, can cause a marked, and often alarming, elevation in the IOP reading obtained (Komaromy and others 2006, Broadwater and others 2008, Klein and others 2011).

In veterinary patients, tonometry is usually performed using digital, indentation, applanation or rebound techniques. In digital tonometry, the index finger is placed on the upper eyelid of the closed eye and the globe is palpated. This method of tonometry is not very sensitive but can help distinguish between a relatively ‘soft’ and ‘hard’ eye.

The Schiotz tonometer was introduced in 1905 and soon became, and remains, …

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