Figure 3 (A) is a normal canine fundus; (B) is a canine fundus with chronic glaucoma showing optic nerve cupping, tapetal hyperreflectivity, and retinal vascular attenuation.
When to Consider Referring
Time is imperative when managing and/or referring a glaucoma case. If you do not have a tonometer or are unsure of diagnosis, cause (primary or secondary), or chronicity, call a veterinary ophthalmologist for advice and/or referral. Evaluation through digital palpation of the globe alone is not acceptable. If there is good comfort level with your diagnosis and appropriate medications are accessible, then initiate treatment immediately, even prior to referral. The client must understand that surgical intervention combined with medications may be necessary to effectively manage glaucoma and that irreversible blindness may ensue, even when all appropriate interventions are employed.
The Referral Process
When calling an ophthalmologist for advice or referral, start the conversation with the dog’s signalment. Describe both eyes (some subtle signs may indicate a problem in the seemingly unaffected eye) and provide medications used and dose information. Inform the client of the approximate cost of an initial referral examination, which will be provided by the veterinary ophthalmologist. Typically, a referral letter is generated following the evaluation. A complete ophthalmic examination includes:
● Direct and consensual PLRs
● Schirmer’s tear test
● IOP measurement
● Fluorescein staining
● Evaluation of the extraocular/intraocular structures, including slit lamp evaluation and binocular indirect ophthalmoscopy.
If medical therapy is unsuccessful, surgical options for animals that have vision or the potential for vision include traditional or endolaser diode laser cycloablation, gonioimplants or glaucoma valves, or a combination of both.
When Referral Is Not an Option
Be prepared—medical management of glaucoma can be frustrating. Educating clients is the key to securing their tolerance and patience. Even after appropriate and aggressive medical management, glaucoma can progress. It can become recalcitrant to therapy if the patient is not periodically reevaluated with medications adjusted to maintain IOP in the safe range. For my well-managed glaucoma patients, a safe IOP is below 20 mm Hg. If IOP rises into the low 20s or higher and medications are at a maximum, call a veterinary ophthalmologist. Intraocular pressure in dogs does not always slowly increase over time, but pressure spikes frequently occur that can be blinding. Treating and/or preventing these spikes is of utmost importance. Monitor IOP once or twice a week for the first month to ensure that therapy is adequate.
Table 1
Treatment options by stage are discussed in Table 1. Once IOP is consistently below 20 mm Hg for a 12- to 24-hour period, medical management (Table 2) is continued and rechecked periodically. If IOP does not drop significantly or is still above 30 mm Hg, it is unlikely that continued medication will decrease the IOP. If the animal is blind and IOP is above 30 mm Hg, pain is likely and a fair suggestion to the client is enucleation or ciliary/chemical ablation to alleviate discomfort. Another palliative surgical procedure is evisceration with intrascleral prosthesis placement; this procedure is usually only available through a veterinary ophthalmologist.
Table 2
Pain Management
Glaucoma pain results from elevated IOP and is proportional to its magnitude. The only way to control the pain is to decrease IOP. Nonsteroidal antiinflammatory medications are contraindicated with primary glaucoma; they can elevate IOP in canine patients and will not diminish pain. Humans with glaucoma have migraine-like headaches, nausea, vomiting, and profuse sweating. Animals with glaucoma are also in significant pain; however, their stoic natures often hide their discomfort. Tramadol may be used to help with pain; however, it has not been evaluated for this purpose in glaucoma.