Glaucoma

Question 1

glaucoma

Answer 1

is defined as damage to the retinal ganglion cells and optic nerve due to increased IOP (intraocular pressure).

Question 2

Normal IOP in the dog

Answer 2

10-20 mmHg. Younger animals are usually on the higher end of normal and older animals are closer to the lower end.

Question 3

Normal IOP in the cat

Answer 3

Cats may be slightly higher, mostly due to sympathetic tone.

Question 4

Normal IOP in the horse

Answer 4

Horses range from about 12-26mmHg.

Question 5

Clincial signs of glaucoma (some or all):

Answer 5

• Enlarged globe (buphthalmos)
• Loss of vision
• Episcleral injection (deep vessels)
• Corneal edema
• Dilated pupil, non responsive
• Striae (linear breaks in the endothelium)

Question 6

Primary glaucoma:

Answer 6

Breed related, inherited. These animals will develop glaucoma
in both eyes over time. The genetics and pathophysiology are poorly understood.

Question 7

Secondary glaucoma

Answer 7

Lens luxation/subluxation
Uveitis
Cataract
Ocular neoplasia
Retinal detachment
Hyphema

Question 8

Acute glaucoma:

Answer 8

Treated as an emergency

Rapidly decrease IOP

Question 9

Dorzolamide/Timolol:

Answer 9

Dorzolamide is a topical CAI (carbonic anhydrase inhibitor); CA is required in the synthesis of aqueous, and when inhibited, results in decreased production of aqueous.
Timolol is a beta blocker and decreased aqueous production by vasoconstriction.
This is not the most rapid drug to use to decrease the pressure, but it can be used in the

Question 10

Latanoprost 0.005%

Answer 10

Latanoprost is a synthetic prostaglandin. Prostaglandins are mediators of inflammation and the mechanism of the drug is similar to naturally occurring uveitis, which causes a decrease in aqueous production and increases aqueous outflow via alternate pathway (uveoscleral).

Question 11

Caveat of using latanoprost

Answer 11

Latanoprost causes the pupil to be extremely miotic (similar to uveitis) which impairs the ability to visualize the fundus & lens when referred.

Question 12

contraindication of latanoprost

Answer 12

DO NOT USE Latanoprost with an ANTERIOR LENS LUXATION (traps vitreous in pupil and lens anteriorly) or GLAUCOMA SECONDARY TO UVEITIS (prostaglandin-worsen uveitis, increases IOP).
This should be only be used under the supervision of an ophthalmologist.

Question 13

IV Mannitol:

Answer 13

If IOP > 40mmHg, and the pressure does not respond to Dorzolamide/Timolol or Latanoprost, mannitol can be given to “dehydrate” vitreous.Not used for glaucoma secondary to uveitis as the choroidal vessels are more permeable allowing mannitol molecules to cross into the vitreous, bringing water with it resulting in increased IOP.

Question 14

If uveitis is present with glaucoma

Answer 14

AVOID latanoprost and mannitol.
AVOID atropine as it will increase IOP further.
Give oral NSAID
Apply topical Prednisolone acetate if NO corneal ulceration or Diclofenac if corneal ulcer is present.

Question 15

ultimate treatment for glaucoma

Answer 15

enucleation

Question 16

Clinical signs of chronic glaucoma

Answer 16

-Buphthalmia – enlarged globe, outer fibrous tunic stretches in response to high pressure
-Corneal edema-variable in cats & horses, seen in most dogs
-Dilated pupil – absent PLR
-Absent menace
-Pain ** do not overlook this because the dog is blind –it may not be obvious until the
eye has been removed. Some animals are just less active than usual.
-Episcleral injection – large straight vessels congested over sclera
-Corneal striae – “stretch marks” in stroma from breaks in endothelium-white streaks
-Retinal degeneration (hyperreflectivity, vascular attenuation)
-Cupped optic disc – loss of myelin and nerve fibers, depressed nerve head

Question 17

surgical options for glaucoma

Answer 17

Enucleation
Evisceration with prosthesis NOT ON CATS
pharmacologic ablation (not for cats, not effective in general)

Question 18

feline glaucoma - what breed

Answer 18

siamese

Question 19

Secondary glaucoma in cats

Answer 19

occurs with uveitis, intraocular neoplasia, hemorrhage and lens luxation.

Question 20

Aqueous misdirection syndrome

Answer 20

This is unique to the cat. Aqueous is directed into the vitreous through a rent in the vitreal face, causing the lens/iris to be anteriorly displaced leaving a very shallow anterior chamber –the differential for aqueous misdirection syndrome is lens luxation. Treatment is challenging. There may be response to Dorzolamide/Timolol, but lens removal may be necessary to control pressure and save vision.

Question 21

Treatment for feline glaucoma:

Answer 21

One drop every 12 hours is recommended. Timolol is a beta blocker and has systemic effects when applied topically; use caution if cardiac or respiratory disease exists.
Carefully examine the patient for evidence of uveitis or lens instability as these are often the underlying cause of glaucoma in cats.

Question 22

What drugs are not appropriate for glaucoma

Answer 22

Steroids are NOT appropriate treatment for glaucoma.

Dilation of the pupil may cause pressure spikes in animals with lens instability or patients predisposed to glaucoma.