What is Glaucoma?
Glaucoma is a complex eye disease that damages the retina and optic nerve, primarily due to increased intraocular pressure (IOP). The eye continuously produces a fluid called aqueous humor, which normally drains out to maintain balanced pressure. However, if the fluid cannot drain properly, pressure inside the eye rises above the normal level (less than 25mmHg in dogs).
This increased pressure:
- Damages the retina, affecting vision.
- Reduces blood flow to the retina and optic nerve, leading to further damage.
If left untreated, glaucoma can cause permanent blindness. Additionally, it is often painful, with humans describing the sensation as similar to a constant migraine. Early detection and treatment are crucial to preserving vision and reducing discomfort.
What causes Glaucoma?
Glaucoma is classified as either primary or secondary. Primary glaucoma occurs when a dog’s natural eye drainage system is faulty, often due to genetics. Breeds predisposed to this condition include American Cocker Spaniels, Shiba Inus, Basset Hounds, Siberian Huskies, Shar Peis, Border Collies, Hungarian Vizslas, Leonbergers, Bouvier des Flandres, English Springer Spaniels, Boston Terriers, Chow Chows, and Miniature Schnauzers.
Secondary glaucoma results from other eye conditions that obstruct fluid drainage, causing pressure buildup. Common causes include cataracts (past or present), lens luxation, intraocular inflammation (uveitis), bleeding, or tumors. Identifying the type of glaucoma is key to effective treatment and management.
How to diagnose glaucoma?
Glaucoma is diagnosed based on clinical signs and diagnostic tests. Common signs include eye enlargement, redness (scleral vascular engorgement), squinting, excessive tearing, a glassy or hazy cornea, vision disturbances, and pupil dilation. A key diagnostic tool is a tonometer, which measures increased intraocular pressure (IOP).
Determining whether glaucoma is primary or secondary is essential for treatment. A veterinary ophthalmologist will perform a comprehensive eye exam to assess IOP levels, evaluate vision loss, and identify underlying causes. A procedure called gonioscopy may also be used to examine the eye’s fluid drainage pathways, helping to confirm a diagnosis and guide treatment options. A procedure called a “gonioscopy” may be performed to evaluate the opening of the fluid drainage pathway out of the eye.
Additional Testing for Glaucoma
If further evaluation is needed to determine whether the glaucoma is primary or secondary, your veterinary ophthalmologist may recommend a specialised imaging test called ultrasound biomicroscopy (UBM). This advanced ultrasound technique provides a detailed view of the entire drainage pathway within the eye, allowing for a more precise diagnosis.Since UBM requires high-resolution imaging of delicate eye structures, sedation is typically necessary to ensure the pet remains still during the procedure. This test can help detect abnormalities in the drainage system, confirm structural defects, or identify hidden causes of fluid buildup, guiding the most effective treatment plan.
Assessing Optic Nerve and Retinal Damage
To evaluate the extent of damage to the optic nerve or retina, a specialised imaging test called ocular computed tomography (OCT) may be performed. This advanced scan provides high-resolution, cross-sectional images of the retina and optic nerve, helping to assess structural changes caused by glaucoma.Since precise imaging is crucial, OCT is typically conducted under general anaesthesia to ensure the pet remains completely still. The results can help determine the severity of the disease and guide treatment options to preserve any remaining vision.
Medical Management of Glaucoma
The first step in treating glaucoma typically involves medicated eye drops, which help control intraocular pressure (IOP) by either reducing fluid production in the eye or enhancing fluid drainage. These medications can temporarily slow the progression of the disease and provide relief from symptoms. However, they do not address the underlying cause of glaucoma, and their effectiveness can decrease over time as the disease progresses.
Despite medical therapy, glaucoma is ultimately regarded as a surgical disease. While eye drops can provide short-term pressure control, they often cannot sustain long-term vision preservation. If medication alone fails to keep IOP within a safe range, surgical intervention becomes necessary to prevent permanent damage to the optic nerve and retina.
Monitoring Treatment Effectiveness
To assess how well the treatment is working, your veterinarian may recommend an intraocular pressure (IOP) curve. This procedure involves taking multiple IOP measurements throughout the day rather than relying on a single snapshot reading, which may not reflect overall pressure fluctuations. A day-long monitoring session helps determine whether medical treatment is adequately controlling IOP or if surgical options should be considered.
When Surgery Becomes Necessary
If IOP remains elevated despite medication, surgery is the only effective option to control pressure and protect any remaining vision. Uncontrolled glaucoma not only leads to irreversible blindness but can also cause significant pain due to the pressure buildup inside the eye. Early surgical intervention improves the chances of preserving vision and maintaining long-term comfort for the affected pet.