Glaucoma

Question 1

Glaucoma - pathogenesis?

Answer 1

Ciliary EPITHELIUM produces aqueous humor from posterior -> anterior chamber, and returned to venous circulation @ SINOUS VENOUS SCLERAE (spaces of Fontana)–> GLAUCOMA OCCURS WHEN IOP INCREASES DUE TO BLOCKAGE OF AQUEOUS HUMOR DRAINAGE => OPTIC N. COMPRESSION

Question 2

1º versus 2º glaucoma:

Answer 2

Primary: bilateral disease potential (first eye affected weeks-to-months before second eye is)

Secondary: lens luxation, uveitis, hyphema, intraocular neoplasis, melanocytic alucoma, pigmentary uveitis, trauma, etc.

Question 3

Signs of acute glaucoma disease

Answer 3

• blepharospasm
• mydriasis (due to sphincter m. paralysis)
• corneal edema
• variable vision
• episcleral injection

Question 4

Signs of chronic glaucoma disease

Answer 4

• all acute signs possible
• buphthalmos
• Haab’s striae (streak going across cornea)
• lens subluxation
• cupped optic nerve

Question 5

What is the most common pathogenesis of feline glaucoma?

Answer 5

Chronic uveitis

Question 6

What can aqueous humor misdirection cause in cats?

Answer 6

Aqueous humor misdirection = abnormaly flows behind lens -> lens gets displaced forward

Question 7

Pathogenesis of glaucoma in equine?

Answer 7

2º to equine recurrent uveitis – typically an insidious disease in horses

Question 8

How is glaucoma diagnosed?

Answer 8

Tonometry (rebound, applanation)

A primary means of dx / assessing efficacy of glaucoma therapy

Other: Gonioscopy

Question 9

What IOP values are abnormal

Answer 9

• Absolute numbers
• IOP disparities b/w 2 eyes
• low IOP values (uveitis drops IOP)

Always check both eyes for comparison purposes!

Question 10

Role of tonometry in treating glaucoma?

Answer 10

Re-checks (e.g., AM versus PM IOP readings may be vastly different)

A primary means of dx / assessing efficacy of glaucoma therapy

Similar to BG readings on a diabetic pt throughout the day

• tonometry is not used for early prediction of canine primary glaucoma

Question 11

What is Gonioscopy?

Answer 11

Specialized assessment of the filtration (drainage) angle; requires a specialized lens. Determines likelihood of animal having primary glaucoma based on angle morphology

Gonioscopy is the examination of the iridocorneal angle or “drain” on the inside of the eye. By placing a goniolens on the cornea and allowing the Ophthalmologist to visualize the angle we can assess whether the glaucoma is due to an abnormal drainage angle. It also allows helps determine the risk for the development of glaucoma prior to completing cataract surgery.

Question 12

What are the goals of glaucoma therapy?

Answer 12

1. Maintenance of vision where possible (glaucoma may be reversible if the pt presents acutely)
2. Patient comfort (in all cases!) -> glaucoma is very uncomfortable!
3. Prophylaxis in “at-risk” eyes

“Prophylaxis” = preventing other eye from becoming affected

Question 13

Emergency management of glaucoma: systemic versus topical medications used

Answer 13

Systemic: hyperosmotics (IV mannitol, PO glycerin)

Topical: prostaglandin analogue (latanoprost, bimatoprost)

Precautions with systemic = short-term tx; pt’s with heart issues

Question 14

What are the characteristics of the 3 glaucoma-maintenance medications?

Answer 14

1. Carbonic Anhydrase Inhibitors (CAIs)
2. Miotics & Prostaglandin Analogues (topical)
3. B-Blockers (topical)

Work by suppressing aqueous humor production

Aqueous humor secretion depends on the production of bicarbonate (HCO-3) from carbonic anhydrase II, an isoenzyme found in the non-pigmented ciliary body epithelium. Chemically, carbonic anhydrase catalyzes carbon dioxide (CO2) hydration and conversion to carbonic acid (H2CO3), which freely dissociates into bicarbonate anions and protons. Bicarbonate formation influences fluid transport by affecting Na+, possibly by regulating the pH for optimal active ion transport. Blockade of carbonic anhydrase by CAIs in local tissues reduces the formation of bicarbonate ions, thus reducing fluid transport and IOP.

Question 15

What are the general principles for glaucoma treatment (4)?

Answer 15

This is not a curable disease -> you are pretty much treating the animal until they go blind. The only “real” way to treat glaucoma is via enucleation sx.

Question 16

Why are topical mydriatics contraindicated in glaucoma tx?

e.g., atropine, tropicamide

Answer 16

Mydriasis may contribute to the possible development of angle closure glaucoma b/c pupil dilation further pushes the iris onto the drainage angle // narrows the angle further

Question 17

What are two ways to surgically manage glaucoma WITHOUT enucleation?

Answer 17

• decrease aqueous production via cyclodestructive procedures
• increases aqueous outflow via filtering procedures / aqueous shunts

Question 18

What are salvage procedures for glaucoma?

Answer 18

Enucleation; evisceration / intrascleral prosthesis; chemical ciliary body ablation

intrascleral prosthesis: gut the eye and replace with silicone eye

chemical CB ablation: intravitreal gentamicin injection (blind eyes only! avoid lens puncture; not always effective)