by Noelle La Croix, DVM, Dip. ACVO
Blood in the Eye. Part 1. Primary Intraocular Conditions
Hemorrhage or bleeding into the anterior chamber of the eye is classified as hyphema. The pathogenesis of hyphema is diverse, but a breakdown of the blood ocular barrier (BOB) and subsequent inflammation (uveitis) is usually involved. Except in cases of severe intraocular disease, the differential diagnosis of hyphema does not differ from hemorrhage in other parts of the body (e.g.; hemoabdomen, pericardial hemorrhage). Hyphema can arise secondary to systemic disease, or as a result of primary intraocular conditions (discussed in this first article of two). Primary ocular conditions that cause hyphema include perforating or blunt trauma, uveitis, intraocular cancer, and retinal detachment.
Trauma can result in profound hyphema. Rupture of the globe causes acute decompression of the aqueous chamber and a breakdown of the BOB. Traumatic hyphema can also result from retrograde blood flow into the anterior chamber, via aqueous humor drainage vessels, without disturbing the BOB. The acuteness and severity of the trauma will determine if primarily blood, or fibrin, will fill the anterior chamber in an attempt to stabilize the fibrous cornea and sclera. Blunt trauma can also cause direct compression of the globe and displacement of the aqueous humor. These changes in pressure can rupture uveal vasculature and tear the retina.
Anterior uveitis (inflammation of the iris and ciliary body) is another common cause of hyphema. This inflammatory breakdown of the BOB can introduce red blood cells into the eye. The inflammation may be associated with systemic disease, intraocular cancer, cataract development, trauma, or parasitic infection. Anterior uveitis can also be idiopathic, or arise secondary to keratitis and/or episcleritis. Chronic uveitis can lead to the generation of new fragile blood vessels that can hemorrhage within the eye. The surfaces of the retina and iris are particularly prone to this neovascularization. Glaucoma, ischemia (from retinal detachment), and intraocular cancer can also result in angiogenesis.
Intraocular tumors can bleed directly into the anterior chamber, and they often promote angiogenesis by secretion of vascular growth factors. Tumors that invade the uvea can also disturb the BOB causing uveitis associated with hyphema.
Hyphema can be associated with retinal detachments. The detachment of the retina from its underlying epithelium is characterized either as rhegmatogenous (primary retinal tearing), tractional (pulled by fibrovascular tissue) or exudative (pushed by abnormal fluid accumulation at the choroid). If the retinal tear involves the retinal artery, bleeding can be profound. Long-standing retinal detachments are often associated with neovascularization and subsequent hyphema.
In particularly young animals, hyphema is often associated with congenital and/or heritable disorders. The defective development of the sclera and choroid characteristic of the congenital inherited Collie eye anomaly can result in hyphema. Vitreoretinal dysplasia (congenital inheritance in Labrador retrievers) has been associated with retinal tearing and hyphema. Rupture of a persistent hyaloid artery (an ophthalmic artery that fails to regress in fetal development) can also lead to hyphema.
Any eye presenting with hyphema should be subjected to an ophthalmic examination including Schirmer tear testing, fluorescein staining, and tonometry. A thorough history, physical examination, and other diagnostic tests can expose trauma and/or underlying systemic disease. Ocular ultrasonography can be used to visualize intraocular tumors and/or retinal detachments. The proper diagnosis will guide the appropriate treatment of the animal and its eye.
Systemic diseases that cause secondary hyphema will be explored in Part 2.
Noelle La Croix, DVM, Dip. ACVO
Veterinary Medical Center of Long Island
75 Sunrise Highway
West Islip, New York 11795
(631) 587-0800; fax (631) 587-2006
Figure 1: Ultrasound of a retinal detachment in a dog. The hyperechoic signal labeled “RETINA” is clearly detached from the posterior wall of the globe.