Hyphema is the presence of blood within the anterior (front) chamber of the eye. Hyphema usually indicates bleeding from the iris blood vessels, but the blood may also originate from the ciliary body (tissue behind the iris), choroidal blood vessels (tissue layer beneath the retina), or retinal blood vessels.

Many cats have some level of decreased vision the affected eye(s); however, if only one eye is involved, their behavior is usually normal. Eyes with hyphema may be painful, with symptoms of squinting, increased blinking and tearing. Trauma-induced hyphema is often accompanied by hemorrhages or bruising of the conjunctiva and tissues around the eye.

Bleeding that is extensive or recurrent may completely fill the anterior chamber, resulting in total hyphema and blindness. Eyes with severe hyphema are at increased risk for developing glaucoma (elevated pressure within the eye) and must be monitored closely for this potential complication.

Initially, the color of the blood within the eye appears bright red. The blood may remain unclotted and settle on the floor of the eye. The blood may also clot and turn dark brown or bluish-black with time.

The presence of hyphema can either be a symptom of a serious eye disease or a manifestation of some internal problem elsewhere in the body. While hyphema is often caused by trauma to the eye, spontaneous hyphema may occur with numerous different ocular and systemic disorders. Therefore, it is imperative that the cause of the hyphema be identified immediately.

Prognosis for vision depends on whether the hyphema is mild or severe, whether the pupil can be effectively dilated during treatment, and whether there is bleeding or damage in the back of the eye as well. The presence of severe hyphema, failure to dilate the pupil, hemorrhages in the back of the eye or retinal detachment often results in blindness.

Causes

In general, the causes of hyphema fall into one of several categories:

Induced by blunt or penetrating trauma

Chronic or severe uveitis, which is an inflammation of the iris, ciliary body, and choroid tissues of the eye

Blood clotting disorders from abnormalities in the number or function of platelets and other clotting factors

Systemic hypertension, which is an elevation in arterial blood pressure

Systemic diseases that effect blood clotting or the vessels of the eye, such as certain viral infections (feline infectious peritonitis), some leukemias, and severe elevations in serum proteins.

Retinal detachment or tearing of retinal vessels

Tumors or cancer within the eye or somewhere else in the body

Specific causes that may be involved with the development of hyphema include:

Blunt trauma or injury through the closed eyelids, such as with automobile accidents, blows to the head, and horse-kick injuries

Sharp trauma or injuries that penetrate or perforate the eye

Proptosis of the eye, which is the forward displacement of the eyeball out of the orbit that usually arises from blunt trauma to the head

Uveitis, with bleeding from blood vessels of the iris, ciliary body and choroidal tissues

Systemic hypertension (high blood pressure) associated with diseases such as chronic kidney disease and hyperthyroidism (hyperactivity of the thyroid gland)

Accidental ingestion of rodenticide toxins, such as warfarin or brodifacoum, or the ingestion of rodents that have died from these toxins

Chronic liver disease with decreased production of coagulation factors and vitamin K

Coumadin toxicity from an overdose of this medication (prescribed for the treatment of certain cardiovascular diseases)

Decreased number (thrombocytopenia) or function of platelets

Hyperviscosity syndrome, which develops with extremely high levels of large protein molecules in the bloodstream

Primary tumors of the iris and ciliary body, or other tumors that originate within the eye

Metastatic tumors that have spread to the eye from other parts of the body

Systemic hypertension (high blood pressure) resulting in choroidal, retinal and vitreal body hemorrhage and retinal detachment.

Retinal detachment with bleeding from the choroid and/or torn retinal vessels, resulting from eye trauma, systemic hypertension, uveitis, post-surgical uveitis (e.g. after cataract surgery), and chronic glaucoma resulting in enlargement of the globe with movement of the lens.