A 5-year-old male/castrated, indoor-outdoor domestic shorthair cat presents with a 4-day duration of a cloudy right eye. No other abnormalities are reported by the owner. Physical examination findings are all normal. Ophthalmic examination of the right eye reveals ventral keratic precipitates and mild aqueous flare. Menace reflex is positive and pupillary light reflexes are positive bilaterally. There is slight resting anisocoria with the right pupil smaller than the left. Fundic examination is normal in both eyes.

Critical assessment of the anterior chamber is often overlooked during the ophthalmic examination. The anterior chamber should be assessed for clarity and depth. Abnormalities within the anterior chamber are often key findings for defining the ophthalmic diagnosis. They can also assist in directing the practitioner toward an underlying systemic disease. Similar to the cornea, clarity of the anterior chamber is critical for normal vision.

The anterior chamber is defined as the space between the cornea and iris. It is filled with aqueous humor, a clear fluid produced by specialized epithelium of the ciliary body. The anterior chamber stays formed by the constant rate production and exit of aqueous.

The aqueous is critical for the nutrition of the deep corneal layers and the lens. The anterior chamber is protected by the blood-aqueous barrier (BAB). The BAB is composed of the nonpigmented ciliary body epithelium (primary barrier) and the nonfenestrated iris capillary endothelium (lesser barrier). These epithelial and endothelial barriers are composed of tight junctions and are very effective at allowing only select nutrients into the anterior chamber. Uveitis is defined as inflammation of the highly vascularized uvea that includes the iris, ciliary body, and choroid. When the anterior uvea (iris and ciliary body) becomes inflamed from trauma, disease or blood-borne pathogens inflammatory mediators, especially prostaglandins, are released and cause a breakdown of the BAB. Depending on the severity and cause of the insult, this can lead to abnormalities of the aqueous including the presence of excessive protein (aqueous flare), blood (hyphema), white blood cells (hypopyon), or fibrin. Abnormal aqueous due to inflammation can affect the health of the cornea and the lens, causing corneal edema or cataract, respectively. Abnormal aqueous can also lead to impaired aqueous outflow and a subsequent increase in intraocular pressure (secondary glaucoma). Anterior uveitis and glaucoma are both painful and vision-threatening diseases. Cataract secondary to anterior uveitis is vision threatening and generally not amenable to surgical correction.