Gluacoma Flashcards
(18 cards)
What is glaucoma and what causes the rise in intraocular pressure (IOP)?
Glaucoma is a group of ocular diseases causing progressive retinal ganglion cell death and optic nerve degeneration. The primary cause of increased IOP is impaired outflow of aqueous humour, produced mainly by the ciliary body. Blockage at the iridocorneal angle leads to pressure buildup, impairing blood and axoplasmic flow in the optic nerve.
Describe the normal physiology of aqueous humour (AH) production and drainage.
AH is produced in the posterior chamber by the nonpigmented ciliary epithelium via active secretion (mainly via carbonic anhydrase), diffusion, and ultrafiltration. It flows through the pupil into the anterior chamber and drains through the iridocorneal angle (conventional route) or via the uveoscleral pathway (unconventional route).
How is glaucoma classified by etiology?
Glaucoma is classified as congenital (rare, due to developmental defects), primary (hereditary, bilateral but asynchronous), and secondary (caused by other ocular diseases). Primary types include open-angle, narrow/closed-angle, and goniodysgenesis-related. Secondary glaucoma is the most common in cats and results from uveitis, lens luxation, cataracts, hyphaema, or tumors.
List common causes of secondary glaucoma.
Secondary glaucoma causes include anterior uveitis, lens luxation or subluxation, cataracts (especially intumescent), aphakia, hyphaema, intraocular neoplasia, pigment dispersion, postoperative ocular hypertension, and malignant glaucoma.
Which dog breeds are predisposed to primary glaucoma?
Breeds include American and English cocker spaniels, Basset hounds (ADAMTS17), Beagles (ADAMTS10), Border Collies (OLFML3), Shar-Peis, Golden retrievers, and more. It often appears between 4 and 10 years of age and has a genetic basis linked to iridocorneal angle malformations.
What are the clinical signs of acute congestive glaucoma in dogs?
Signs include pain (blepharospasm, tearing), redness (episcleral engorgement), corneal edema, sluggish or dilated pupil, decreased menace response, and visual loss. Buphthalmia and optic disc cupping occur in chronic stages.
How does glaucoma present differently in cats compared to dogs?
Cats often show fewer overt signs, even with high IOP. Pain is less noticeable, and corneal edema or conjunctival hyperemia usually appear in late stages. Vision loss is often delayed, and diagnosis occurs at a more chronic stage.
How is intraocular pressure (IOP) measured and what values indicate glaucoma?
IOP is measured using applanation (Tono-Pen) or rebound (TonoVet) tonometers. Normal IOP is 12–25 mmHg in dogs and 12–27 mmHg in cats. Values >25 mmHg in dogs or >27 mmHg in cats with clinical signs indicate glaucoma.
What is gonioscopy and how is it used in diagnosing glaucoma?
Gonioscopy is the examination of the iridocorneal angle using a specialized lens under topical anesthesia. It helps classify the type of glaucoma (open, narrow, closed angle, goniodysgenesis) and identify angle infiltration in secondary glaucoma. Usually performed by specialists.
What fundoscopic findings are seen in glaucoma?
In acute glaucoma: optic disc swelling and peripapillary edema. In chronic stages: disc cupping, increased tapetal reflectivity, retinal vessel attenuation, and optic nerve atrophy.
Which imaging method is useful when intraocular structures can’t be visualized directly?
Ocular ultrasound is used when corneal edema or other opacities prevent fundus examination. It helps detect causes like intraocular masses, lens luxation, uveitis, or retinal detachment.
What is the first-line emergency treatment for acute primary glaucoma in dogs?
Topical prostaglandin analogues (e.g., latanoprost, travoprost) are first-line agents. They rapidly increase aqueous outflow, reducing IOP by up to 60%. Used cautiously in uveitis or lens luxation due to potential side effects like miosis and inflammation exacerbation.
What role do carbonic anhydrase inhibitors (CAIs) play in glaucoma treatment?
Topical CAIs (e.g., dorzolamide, brinzolamide) decrease aqueous humor production and are effective in all glaucoma types. Oral CAIs have more side effects and offer no additional benefit when combined with topical agents.
What are the risks and indications of using timolol in glaucoma patients?
Timolol is a topical beta-blocker used with CAIs to reduce aqueous production. Risks include bradycardia, hypotension, and bronchospasm. It should be avoided in animals with cardiac or respiratory disease and used with caution in uveitis or lens luxation cases.
When is mannitol used in glaucoma, and what are its limitations?
Mannitol, an osmotic agent, is used in emergency treatment of acute glaucoma. It draws fluid from the vitreous and reduces AH production. Contraindicated in cardiac/renal patients and when the blood-aqueous barrier is compromised. Not for long-term use.
How is secondary glaucoma managed differently from primary glaucoma?
Treatment focuses on addressing the underlying cause (e.g., treating uveitis, removing lens luxation). PGAs may be contraindicated depending on the etiology. Medical management is similar but tailored to the specific cause.
What are the long-term management options for primary glaucoma?
Includes regular IOP monitoring, prophylactic treatment of the contralateral eye, and potentially surgery (e.g., cyclodestruction, filtering procedures). Enucleation or intrascleral prosthesis may be necessary for blind, painful eyes to improve quality of life.
What is the prognosis for primary versus secondary glaucoma?
Primary glaucoma has a poor long-term prognosis due to progressive optic nerve damage. Secondary glaucoma prognosis depends on timely control of the underlying cause, with better outcomes possible if addressed early.
