Glaucoma Diagnosis and Management

Equine glaucoma, although relatively rare, is being increasingly recognised in clinical practice and seems to be a sequel to chronic inflammation associated with equine recurrent uveitis (ERU) in the majority of cases. An increased awareness of the disease, along with greater availability of portable tonometry to document intraocular pressure (IOP) elevations, means that more horses are being identified earlier, before significant irreversible vision loss has occurred. Various medical and surgical treatment options now exist and, with prompt and appropriate treatment, the prognosis for preserving vision in these horses is improving.

The glaucomas refer to a diverse group of disorders in which the outflow of aqueous humour (AH) from the eye is impaired leading to abnormal elevations in IOP. These elevations in the IOP damage the neurosensory retina and optic nerve leading to vision loss. Glaucoma is typically classified as congenital, primary or secondary, depending on the nature of the pathology interfering with AH outflow. The pathology usually involves the iridocorneal angle (ICA), which is the angle formed between the base of the iris and the peripheral cornea (also referred to as the drainage or filtration angle). Congenital equine glaucoma has been reported in Thoroughbred, Arabian and Standardbred foals and is associated with developmental abnormalities of the ICA, or in many cases, more severe anterior segment dysgenesis. While primary glaucoma has been reported in the horse, its true existence remains somewhat controversial. In practical terms, if primary glaucoma does exist, it is extremely rare, and the vast majority of cases are secondary to an identifiable underlying cause such as uveitis, lens luxation or intraocular neoplasia. Studies have identified clinical signs compatible with ERU in 85–90% of horses with glaucoma. [...]