Animal intraocular pressure

What is intraocular pressure?

Intraocular pressure (IOP) is the pressure exerted by the contents of the eye (including the lens, vitreous body, uvea, retina, and intraocular fluids—aqueous humor and blood) on the inner wall of the eyeball. It is expressed in millimeters of mercury (mmHg), and the circulation of aqueous humor has the greatest impact on IOP.

In clinical practice, the interpretation of intraocular pressure (IOP) results in animals should not rely excessively on the "normal" IOP range.

01 Physiological Changes ↑↓

Circadian Rhythm: In dogs, normal IOP is highest in the morning and gradually decreases thereafter; in cats and rabbits, normal IOP is lowest in the afternoon and highest in the evening; in horses, normal IOP is higher during the day and lower at night (affected by the light-dark cycle).

Age: Normal intraocular pressure (IOP) in animals decreases with age.

Reproductive Status: IOP increases significantly in female cats during estrus.

02 Pathological Increase (↑)

Glaucoma: Glaucoma is a disease caused by elevated intraocular pressure leading to optic nerve damage. It is common in animals such as dogs and cats.

Anterior Uveitis: Anterior uveitis is an inflammation of the anterior part of the eye that can lead to elevated intraocular pressure. It is common in dogs, cats, and other animals.

Tumors: Tumors of the eye or periocular structures can compress eye structures, leading to elevated intraocular pressure. This is common in animals such as dogs and cats.

Lens Dislocation: Lens dislocation occurs when the lens capsule ruptures and protrudes into the anterior chamber of the eye, causing elevated intraocular pressure. This is common in animals such as dogs and cats.

Hyperthyroidism: Hyperthyroidism can cause bulging and compression of the eyeball, leading to elevated intraocular pressure. This is relatively common in animals such as dogs and cats.

Pyrohemorrhage: Hyrohemorrhage can lead to secondary glaucoma and elevated intraocular pressure. This is relatively common in animals such as dogs and cats.

Other diseases, such as connective tissue disorders, liver disease, and kidney disease, can also lead to elevated intraocular pressure, commonly seen in animals like dogs and cats.

It's important to note that the above-mentioned pathological factors may not be the sole cause of elevated intraocular pressure; other factors can also affect normal intraocular pressure levels. Therefore, a comprehensive assessment and management based on the specific circumstances are necessary for clinical diagnosis and treatment.

03 Pathological Decrease ↓

Post-operative or traumatic wound leakage, ciliary body detachment, ocular wall perforation, severe iridocyclitis, retinal or choroidal detachment.

Excessive extravasation of aqueous humor after glaucoma external filtration surgery.

Systemic conditions, such as myotonic atrophy and conditions leading to hyperosmolarity, such as dehydration, uremia, diabetes, etc.

Vascular occlusive diseases, such as ocular ischemia syndrome, giant cell arteritis, central retinal vein or artery occlusion.

Uveitis leading to ciliary body shock, etc. In uveitis, intraocular pressure (IOP) generally decreases. However, in severe uveitis, IOP may be within the normal range or even tend to increase. In this case, the possibility of secondary glaucoma must be considered, and appropriate treatment should be given.

VI. Influencing Factors

Animal restraint | Traction of the eyelids or pressure on both jugular veins can significantly increase IOP values. This is because jugular venous pressure increases pressure on the extrascleral vascular system, leading to venous stasis.

Medication Effects | Veterinarians should be aware of the effects of certain medications on intraocular pressure (IOP) in animals. For example, topical tropicamide can significantly increase IOP in both normal and glaucoma-affected cats. Compared to cats, topical tropicamide has a smaller impact on IOP in dogs.

Measurement Order | IOP measured in the first eye, whether right or left, is always higher than in the contralateral eye. Repeated IOP measurements during the same visit may result in a significant decrease in IOP, although the magnitude may not be clinically apparent.

Rebound Tonometer LWK-500 is used to measure intraocular pressure, there are two working modes:vertical and horizontal.

Wireless date output. the principle:when the probe contact the sur-face of different hardness at a certain speed, it has different reaction of the probe rebounding.

Advantage: high accuracy, protable,without anesthesia. without the cross-infection etc.