Based on signalment and clinical findings, including evidence of pectinate ligament dysplasia in the unaffected eye, primary angle closure glaucoma is an important differential diagnosis in this case. Other important differentials to consider for a red, cloudy, painful eye include keratoconjunctivitis sicca, corneal ulceration, and uveitis, the latter potentially with secondary glaucoma. Keratoconjunctivitis sicca and corneal ulceration as underlying causes were ruled out, and because the aqueous flare is mild, the uveitis and IOP are likely attributable to primary glaucoma rather than a systemic cause.
Glaucoma is a leading cause of blindness in dogs, with goniodysgenesis-related primary angle closure glaucoma (PACG) being the most common of the primary glaucomas.1-4 Goniodysgenesis refers to abnormal architecture of the iridocorneal angle that contributes to obstruction of outflow of aqueous humor. This abnormality is believed to have an underlying genetic component1-3 and is seen with relatively high prevalence in purebred dogs, including American Cocker spaniels, basset hounds, Siberian huskies, chow chows, and Boston terriers, among others.1
PACG typically manifests as an acutely painful eye with increased IOP and blindness. Some breeds (eg, basset hounds) also have significant anterior uveitis and corneal edema associated with an acute attack, which can be clinically confusing and may complicate treatment.5 Although canine glaucoma is generally associated with elevated IOP (≥50 mm Hg), IOP may fluctuate widely in glaucoma and may in fact be within or lower than the normal range at the time of presentation. This may especially be true of chronic disease involving pressure damage to the ciliary body’s production of aqueous humor or in patients with significant intraocular inflammation, which also can have a negative impact on aqueous humor production.
Prognosis for vision and globe retention is dependent on quick recognition of clinical signs and prompt treatment to decrease IOP, as just a few hours of pronounced IOP elevation can result in blindness. In general practice settings, medical management is the safest and most accessible way to decrease IOP. Prostaglandin analog (eg, latanoprost) therapy, typically coadministered with topical carbonic anhydrase inhibitors (eg, dorzolamide), is the most effective medical therapy for PAC in dogs.6 β-blockers (eg, timolol) also reduce IOP but, when administered alone, their IOP-lowering effect is insufficient7; thus, they should be reserved for prophylactic or adjunctive therapies. Systemic hyperosmotics (eg, intravenous mannitol, oral glycerol) may also be used for marked IOP reduction6,8 but should be used with caution and only after routine blood work (eg, renal values, electrolytes), especially in older or debilitated animals or animals with cardiovascular disease (Table). Surgical interventions in acute cases are typically reserved for patients with a fair-to-good prognosis for vision. These procedures should be performed by a board-certified veterinary ophthalmologist and may include gonioimplants, cyclophotocoagulation (transcleral laser or endolaser), and/or aqueocentesis.