Identify two common causes of secondary glaucoma in horses.

• A. Retinal detachment and conjunctival neoplasia
• B. Anterior chamber hyphema and scleral penetration
• C. Chronic uveitis and lens-related disease (e.g., lens subluxation or cataract)
• D. Bacterial keratitis and corneal ulcers

Answer: (C)

Secondary glaucoma in horses is most commonly driven by inflammatory and lens-related problems that block aqueous humor drainage. Chronic uveitis causes breakdown of the blood-aqueous barrier and formation of inflammatory debris, fibrin, and synechiae that narrow or seal the iridocorneal angle, leading to impaired outflow and rising intraocular pressure. Lens-related disease—such as lens subluxation/luxation or cataract—disrupts anterior segment anatomy and can trigger lens-induced uveitis or physically crowd the drainage angle, producing secondary glaucoma. Other listed conditions don’t typically explain the common pathways to secondary glaucoma in horses, whereas these two are the classic culprits.