Intraocular pressure measurement, crucial for early detection and management of glaucoma and ocular conditions.

Table of Contents

Understanding Intraocular Pressure (IOP)


Intraocular pressure (IOP) refers to the pressure within the eye, exerted by the aqueous humor – the fluid filling the anterior chamber. Maintaining appropriate IOP is crucial for maintaining ocular structure and function, as abnormal pressure levels can lead to ocular discomfort, vision loss, and even blindness.

Importance of IOP Measurement

Measuring intraocular pressure is essential for diagnosing and managing various ocular conditions, including glaucoma, uveitis, and ocular trauma. Monitoring IOP allows veterinarians to assess the risk of optic nerve damage, guide treatment decisions, and evaluate the effectiveness of therapeutic interventions.

Methods of Tonometry

Applanation Tonometry

Applanation tonometry is the gold standard method for measuring intraocular pressure in veterinary medicine. During applanation tonometry, a small probe or prism is applied to the corneal surface to flatten a defined area of the cornea. The force required to flatten the cornea is directly proportional to the intraocular pressure and is measured using specialized tonometers.

Indentation Tonometry

Indentation tonometry is an alternative method for measuring intraocular pressure, particularly in animals with corneal irregularities or small eyes. It involves applying a known force to the cornea using a blunt-tipped instrument and measuring the depth of corneal indentation. The degree of indentation is inversely proportional to the intraocular pressure.

Clinical Significance and Interpretation

Diagnosis of Glaucoma

Tonometry is essential for diagnosing glaucoma, a group of progressive optic neuropathies characterized by elevated intraocular pressure and optic nerve damage. Elevated IOP is a hallmark feature of glaucoma and is a key diagnostic criterion for this condition.

Monitoring Disease Progression

Tonometry is used to monitor disease progression and treatment response in animals with glaucoma. Serial IOP measurements help veterinarians assess the effectiveness of medical therapy, surgical interventions, and other treatment modalities in controlling IOP and preserving vision.

Considerations and Limitations

Anesthesia Requirement

Tonometry requires patient cooperation and immobilization, typically achieved under sedation or general anesthesia. Anesthesia depth and patient positioning can influence IOP measurements, requiring careful consideration to minimize variability and ensure accuracy.

Corneal Thickness

Corneal thickness can affect tonometry readings, as thicker corneas may underestimate IOP while thinner corneas may overestimate IOP. Correction factors based on corneal thickness are often applied to tonometry measurements to account for this variability.


Tonometry is a vital diagnostic tool in veterinary ophthalmology, providing valuable information about intraocular pressure and aiding in the diagnosis and management of ocular conditions such as glaucoma. By understanding the principles, methods, clinical significance, and limitations of tonometry, veterinarians can accurately assess intraocular pressure, monitor disease progression, and optimize treatment strategies to preserve vision and ocular health in their patients.

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