Taking the pressure off: glaucoma and what can be done to help

Glaucoma is a group of eye conditions that damage the optic nerve. Glaucoma can be a difficult ophthalmic emergency to treat and can be classified as primary or secondary.

Primary (hereditary) glaucoma is a congenital abnormality causing a malfunction and malformation of the eye/s, reducing the flow of aqueous humour and often slowly increasing intraocular pressure over time (Reinstein, 2018). Generally, primary glaucoma is a bilateral disease affecting one eye initially, then the second eye 6–18 months later. Primary glaucomas can be further subdivided into two types: primary closed angle glaucoma and primary open angle glaucoma.

Primary closed angle glaucoma (due to goniodysgenesis) is the most common primary glaucoma seen in dogs. Goniodysgenesis, also known as pectinate ligament dysplasia, pectinate ligament abnormality, or iridocorneal angle abnormality, is a dysplastic development of the draining structure. On examination it is visible as pectinate ligament dysplasia, with dysplasia worsening over time, while causing a reduction in flow of aqueous humour (Large and Busse, 2018), which is an inherited risk factor for development of primary closed angle glaucoma in dogs. The condition is graded 0–3 based on its severity – the higher the grade, the higher the risk of glaucoma (Davies The Veterinary Specialists, 2021). This can occur in any breed of dog; however, it is recognised more frequently in the following breeds: American Cocker Spaniel, Basset Hound, Border Collie, Dandie Dinmont, English Cocker Spaniel, English/Welsh Springer Spaniel, Flatcoated retriever, Golden Retriever, Great Dane, Hungarian Vizsla, Japanese Shiba Inu, Leonberger, Siberian Husky, Spanish Water dog and Welsh Terrier. Development of symptoms comes later in life and the degree of pectinate ligament dysplasia can worsen over time, with severely affected patients having an increased likelihood of developing glaucoma (Large and Busse, 2018).