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PeeR Reviewed Clinical Approach to the CAnine Red eye Elizabeth Barfield Laminack, DVM; Kathern Myrna, DVM, MS; and Phillip Anthony Moore, DVM, Diplomate ACVO T he acute red eye is a common clinical challenge for general practitioners. Redness is the hallmark of ocular inflammation; it is a nonspecific sign related to a number of underlying diseases and degree of redness may not reflect the severity of the ocular problem. Proper evaluation of the red eye depends on effective and efficient diagnosis of the underlying ocular disease in order to save the eye's vision and the eye itself.1,2 SOURCE OF REDNESS The conjunctiva has small, fine, tortuous and movable vessels that help distinguish conjunctival inflammation from deeper inflammation (see Ocular Redness algorithm, page 16). • Conjunctival hyperemia presents with redness and congestion of the conjunctival blood vessels, making them appear more prominent, and is associated with extraocular disease, such as conjunctivitis (Figure 1). If severe intraocular inflammation is present, conjunctival hyperemia can also occur in conjunction with episcleral injection.1 • Subconjunctival hemorrhage appears as amorphous areas of deep red below the conjunctiva, obscuring the view of the individual vessels. Subconjunctival hemorrhage occurs in over-restraint, traumatic injury, clotting disorders, and strangulation (Figure 2).1 • Episcleral injection causes redness because of conges- 1A 1B Figure 1. Ventral palpebral conjunctival hyperemia and chemosis secondary to allergic conjunctivitis (A); note small, fine, tortuous vessels and lymphoid vessels (B). 12 Today's Veterinary Practice May/June 2013 tion of the deep episcleral vessels, and is characterized by straight and immobile episcleral vessels, which run 90° to the limbus. Episcleral injection is an external sign of intraocular disease, such as anterior uveitis and glaucoma (Figures 3 and 4). Occasionally, episcleral injection may occur in diseases of the sclera, such as episcleritis or scleritis.1 • Corneal Neovascularization È Superficial: Long, branching corneal vessels; may be seen with superficial ulcerative (Figure 5) or nonulcerative keratitis (Figure 6) È Focal deep: Straight, nonbranching corneal vessels; indicates a deep corneal keratitis È 360° deep: Corneal vessels in a 360° pattern around the limbus; should arouse concern that glaucoma or uveitis (Figure 4) is present1,2 • Hyphema or hemorrhage within the eye appears as either a: È Settled line of dull to bright red in the anterior chamber È Diffuse redness filling the entire chamber (Figure 7). Hyphema can result from clotting disorders, severe blunt trauma, or uveitis, and can be associated with systemic hypertension. DISEASES & DIAGNOSTICS All red eyes must be evaluated for 3 key ocular diseases that may cause vision loss in an eye (Table 1, page 14): 1. Corneal ulceration 2. Glaucoma 3. Uveitis A few basic diagnostic procedures can quickly assess whether these diseases are present; they should be performed in the following order for all patients with ocular signs: 1. Schirmer tear test (STT): Aids in diagnosis of conditions associated with decreased tear production, such as keratoconjunctivitis sicca (KCS), and should be performed before any medications are administered to the ocular surface 2. Fluorescein stain: Is critical for diagnosis of corneal ulceration1,2 3. Tonometry: Is critical for diagnosis of glaucoma and uveitis1,2