11,12 - Glaucoma Flashcards
Glaucoma is an _______ intraocular pressure above which the ____ ____ and ____ cannot function and ocular pathology results.
increased; optic nerve; retina
Which cells are the first to be damaged in glaucoma cases?
Ganglionic cells - layer closest to the inside of the eye which is very sensitive to increased IOP
IOP in glaucoma is the result of an impediment of the flow of ____ ______.
Aqueous humor
IOP has diurnal viaration. In dogs, IOP is greatest in the _____. In cats, IOP is greatest in the ______.
What is the clinical significance in this?
Morning; evening
If you suspect glaucoma in a dog, measure IOP in the morning.
If you suspect glaucoma in a cat, measure IOP in the evening.
In respect to IOP:
Low blood flow to the eye _____ IOP.
Pulling on the animal’s collar _____ IOP.
decreases; increases
General anesthetics typically decrease IOP. What anesthetic is the exception and actually causes an increase in IOP?
Ketamine - so avoid ketamine in glaucoma patients
T/F: Ocular inflammation increases IOP.
FALSE - decreases IOP b/c inflammation increases aqueous ouflow and prostaglandins from inflammation decrease aqueous production
T/F: Glaucoma always must be addressed aggresively and immediately.
True - vision is fragile and can be lost quickly
Glaucoma is one of the most commonly _______ eye conditions in animals, due to failure of owners to recognize disease early and failure of clinicians to recognize onset in the second eye, preventing the ability to regain eyesight.
misdiagnosed
Glaucoma history: 4 questions to ask
- What signs first mad you think your dog had an eye problem? (red, bumping into things on one side)
- How long have you noticed a problem?
- Have you noticed any decrease in your pet’s activity or appetite?
- If the animal is blind, how long has the blindness been present?
If an animal with glaucoma has been blind for over ___ hours, prognosis to regain vision is poor.
24
C/S of acute glaucoma:
- Corneal edema
- Recent vision loss
- Partial vision loss
- Enlarged episcleral vessels (pressure in the eye closes off the venous return from the eye)
- Ciliary flush (hedge vessels - 360 degree neovasculization)
- Dilated pupil (due to retinal damage and pressure effects on the iris sphincter muscle)
C/S of chronic glaucoma include acute signs, plus:
- Chronic blindness
- Buphthalmos (big globe)
- Lens luxation +/- aphakic crescent
- Haab’s striae
- Posterior segment signs:
- Retinal degeneration
Cupped optic nerve head
- Retinal degeneration
Why does lens luxation in glaucoma patients?
As the eye becomes larger due to pressure elevation within the globe, the zonular attachments stretch and can break, causing the lens to luxate.
Therefore, the lens luxates as a secondary problem to glaucoma, NOT a primary problem.
Haab’s Striae is a C/S in chronic glaucoma. What is it?
Haab’s straie appear as white linear demarcations in corneal endothelium. These are microbreaks in descemet’s membrane due to the stretchin of the globe from increased IOP.
Can be incidental in horses, but common sign of chronic glaucoma in dogs and cats.
Why do we see a cupped optic nerve head as a result of chronic glaucoma?
As the pressure in the eye is elevated, the path of least resistance is through the lamina cribrosa at the level of hte optic nerve, resulting in tissue to be pushed back at this location, causing damage to the nervous tissue, leading to blindness.
T/F: Retinal degeneration and cupped optic nerve head are reversible changes in chronic glaucoma.
False - irreversable! Lead to blindness
Why do we see episcleral hyperemia in glaucoma patients?
Increased IOP compresses sclera and impedes normal venous drainage
Why do we see mydriasis in glaucoma patients?
Impaired blood flow or innervation to iris
Why do we see blephorospasms in glaucoma patients?
Pain
Why do we get blindness in glaucoma?
Retinal AND optic nerve ischemia and necrosis
In glaucoma, which gets lost first, central or peripheral vission?
Peripheral
Why do we see buphthalmia in glaucoma patients?
Stretching of the globe from chronic IOP elevations
Histopath description of retina with glaucoma:
- Inner retinal degeneration
- Ganglion cell loss
- Chronic cases have diffuse retinal degeneration
T/F: Human glaucoma is very similar to dog glaucoma.
False - dogs have more of an acute stage of glaucoma with very high increases in pressure, causing it to be more painful and increased risk of vision loss compared to humans.
Primary glaucoma occurs in the absecne of….
other ophthalmic disease
T/F: Primary glaucoma is breed related and presumably inherited.
True
Primary glaucoma is a disease at the level of the _______
Iridocorneal angle (drain part - outflow issue)
Two mechanisms of primary glaucoma that both lead to decreased aqueous fluid draining from the eye:
- Abnormal formation of the iridocroneal angle with progressive narrowing
- Biochemical changes in the trabecular meshwork
List some common breeds associated with primary glaucoma
Basset hound
Cocker spaniel
Bouviet de flanders
Husky
Beagle
Norwegian elkhound
Shih tzu
Secondary glaucoma occurs secondary to other primary intraocular disease. List three examples of primary intraocular disease that can lead to glaucoma:
Uveitis
Neoplasia
Lens luxation
How can uveitis lead to glaucoma:
Inflammatory debris can get into the iridiocorneal angle, and decrease the ouflow of aqueous humor
T/F: Congenital glaucoma is a rare, severe disease that occurs in animals less than a year of age.
True
T/F: Digital pressure is a good diagnostic for testing for glaucoma.
False - not good enough
The ideal diagnostic testing methods for glaucoma are using automated tools for measuring IOP - list the two examples:
Applanation (tonopen)
Rebound (tonovet)
How can we diagnose retinal degeneration and optic nerve cupping in glaucoma patients?
Funduscopy
What is the #1 reason to measure intraocular pressure (IOP)?
Red eye - IOP should be determined in every red eye with an intact cornea and sclera.
Contraindications for measuring IOP?
Perforated eye
If perforation potential (descemetoceles, or deep stromal or metling ulcers)
Besides red eye, what are other good reasons to test IOP?
- Genetic reasons
- Part of MOD
- Monitoring uveitis cases
- Monitoring in ophthalmic surgery cases
Shiotz tonometry reqires a ______ cornea, so it cannot be practically done in the horse.
horizontal
When obtaining an accurate measurement of IOP, it is important to hold the lid open by holding against the _____ rim and not against the eye.
Orbital
T/F: In tonometry - the highest reading is the most accurate.
False - lowest final reading is the most accurate!!
In tonometry, if both eyes are normal, there should be no more than a ____ mmHg pressure difference between the eyes.
5
What are normal IOP measurements in the dog, cat and horse?
- Dog = 12-24 mmHg
- Cat = 12-27 mmHg
- Horse = 17-29 mmHg
Easy way: cats and dogs are between 10-20; horses can go much higher - 20-30
Two mechanisms of aqueous ouflow:
- Conventional route - produced in the ciliary body epithelium and exits through pupil and into the iridocorneal angle (‘drain’ part of the eye)
- Unconventional route - uveoscleral ouflow (transported from ciliary body into the lymphatics)
What diagnostic method can be used to visualize the iridocorneal angle and determine if glaucoma is primary or secondary?
Gonioscopy
Upon gonioscopy of the eye, a normal iridocrneal angle has an ____ angle, while an eye affected with primary glaucoma will have a ___ or ____ angle.
open; narrow; closed
What is goniodysgenesis?
Thickened pectinate ligament fibers - causes a thickened sheet of tissue across the iridocorneal angle with dark focal spots.
This closes off the iridocorneal angle due to this thick sheet of tissue (it is like a drain clogged with hair).
This is also causes primary glaucoma
Primary glaucoma is a bilateral disease, where it affects one eye first and the second eye about ____ months later.Very rarely are both eyes affected at the same time.
8
Two glaucoma tx methods that aid in decreasing IOP include:
Decrease aqueous production (turn down the faucet)
Increase aqueous ouflow (help drainage)
T/F: Glaucoma typically comes out of remission about 6 months after it has been treated.
True
List three common adrenergic antagonist drugs used in treating glaucoma
Timolol maleate (beta-blocker)
Betaxolol (beta1 selective-blocker)
Cosopt (dorzolamide/timolol combo)
List two common carbnoic anhydrase inhibitors used to tx glaucoma:
Trusopt (dorzolamide)
Cosopt (Dorzolamide/timolol combo)
List a common prostaglandin analog used to tx glaucoma:
Latanoprost (xalatan)
Osmotic agents, cholinergic agonists, and some adrengergic agonists (epinephrine and derviates specifially) decrease IOP how?
By increasing aqueous ouflow
Beta blockers, carbonic anhydrase inhibitors (CAIs), and some adrenergic agonists (alpha-2 agonists specifically) decrease IOP how?
By decreasing aqueous production
How do prostaglandins lower IOP?
Decreasing aqueous production AND increasing aqueous ouflow
T/F: Cholinergic agonists increase aqueous ouflow via the conventional pathway by increasing aqueous ouflow, and can cause marked miosis.
True
T/F: cholinergic agnoists are one of the first line txs for glaucoma.
False - last ditch attempt used by ophthamologists
It is a compounded drug that is not commercially available, and is irritating.
Demecarium bromide and pilocarpine are cholinergic agonists that are very irritating. Pilocarpine specifically can induce ____.
Therefore, these durgs are a last ditch effort tx by ophthamologists.
Uveitis
Beta-adrenergic blockers affect the _____ nervous system, specifically blocking beta-adrengergic receptors in the non-pigmented ____ _____ _____ when given topically, ultimately ____ aqueous production.
sympathetic; ciliary body epithelium; decreasing
T/F: Beta-blockers are best used prophylactically in the fellow eye.
True
Beta blockers are often given in combination with which other drug to enhance glaucoma tx:
Carbonic anhydrase inhibition
T/F: Beta-blockers work very well when given as a single drug in an affected glaucoma eye.
False - used alone prophylactically; or in combo with CAIs to tx glaucoma eye
What is an uncommon side effect of timolol?
Bradycardia - bigger deal in smaller dogs
Timolol can cause pulmonary bronchoconstriction in patients with asthma. Is this clinically significant in dogs? Cats?
Not in dogs - becuase dogs do not get asthma.
Not an issue with cats becuase even though they get asthma, they rarely get glaucoma and if they do have glaucoma - we use other txs besides beta-blockers to treat.
What makes betaxolol different from timolol maleate?
Betaxolol is a beta-1 selective adrenergic blocker; while timolol is a non-selective beta 1 and 2 blocker.
Therefore, it is thought that betaxolol has less cardio/respriatory side effects in patients.
T/F: Osmotic diuretics are a great long term tx in patients with glaucoma.
False - only used short-term - rescue drug until sx or medical tx
Mechanism of action in osmotic diuretics for tx of glaucoma
Rapid increase in serum osmolality –> expansion of blood volume, and systemic dehydration (will draw fluid out of the eye and decrease IOP short-term) –> shrinking of vitreous
How is mannitol administered?
What is the dose?
1-2 g/kg IV over 20 minutes
T/F: Diabetics cannot be given mannitol becuase it is a sugar.
False - mannitol is a sugar, but it is NOT metabolized, and instead it is excreted in the urine, so it can be used in diabetics
Mannitol can crystalize, what can you do to avoid this?
Keep warm
Why do we give mannitol slowly, over the course of 20 minutes?
Becuase of the crystals present
T/F: It is important to keep giving the animal a lot of water when tx with mannitol
False - we want to withold water, but be careful to not dehydrate the animal - so feed icechips
T/F: Carbonic anydrase inhibitors do not change the pupil size.
True
In which type of glaucoma (primary or secondary) do we NOT want to change the pupil size? Which class of drugs would be contraindicated in tx?
Secondary - avoid cholinergic agonists becuase they decrease pupil size (miosis)
Carbonic anhydrase inhibitors when given topically as the only drug to stop glaucoma, how often should it be given daily?
TID
T/F: Oral CAIs like methazolamide and acetezolamide are very common to use in vet med to tx glaucoma.
False - difficult to obtain, and obsolete in human medicine.
Where are carbonic anydrase enzymes located and what do they do?
Located in the non-pigmented ciliary body epithelium
The enzymes catalyze the reaction:
CO2 + H2O –> HCO3- + H+
As HCO3 crosses into aqueous humor, it draws Na+ and water with it to produce aqueous humor.
CA inhibitors will inhibit these enzymes, reducing amount of HCO3 produced, and subsequently decrease aqueous humor production
Why should we avoid oral CAIs?
They will inhibit ALL carbonic anydrase enyzmes in the body - this includes the kidneys, causing hypokalemia, metabolic acidosis, and compensatory respriatory alkalosis.
And the GIT - causing vomiting and diarrhea.
T/F: Topical CAIs can also have systemic side-effects.
False - only effect carbonic annhydrase in the eye
T/F: Cosopt is a combination of dorzolamide and timolol and is better than either drug alone.
True
When dorzolamide is combined with timolol, what is the daily dosing?
BID
T/F: Synthetic prostaglandins can cause uveitis, just like natural prostaglandins.
False - synthetic prostaglandins do not cuase uveitis
Endogenous prostaglandins can result in miosis, uveitis, and _____ IOP.
reduced
Prostaglandin analogs increase ____ aqueous ouflow, but can also _____ aqueous production.
Unconventional; decrease
T/F: Prostalandin analogs are a useful rescue therapy because of the profound decrease in IOP within 20-30 minutes.
True
Side-effects of prostaglandin analogs include:
Intense miosis
May decrease peripheral vision a little
May exacerbate uveitis if already present
Conjunctival hyperemia
What can be givin in combination with prostaglandin analogs to decrease their side effects?
Very small doses of NSAIDs/steroids
Prostaglandin anaglos are ineffective in lowering IOP in what species? WHy?
Cats - they do not have the receptor that binds with the synthetic PGF
Glaucoma surgical therapy includes laser cyclophotocoagulation, which is laser ablation of the _____ _____.
Ciliary body (decreases aqueous production)
Two types of laser cyclophotocoagulation
- Trans-scleral
- Blind approach from the outside
- Endolaser
- Intraocular approach
- Specifically tragets the ciliary body
- More effective than trans-scleral, but more expensive
Goniovalve is a glaucoma surgical therapy that ____ aqueous outflow.
Increases
T/F: Goniovalve is a great glaucoma sx therapy when used alone to tx glaucoma.
False - only given in combination with laser tx
What is a goniovalve?
One-way valve placed ontop of the sclera, but underneath the conjunctiva, that drains fluid into the subconjunctival space.
Side effects of the goniovalve
Fibrosis in dogs
Debris will block the valve
What are three glaucoma surgical therapy comfor preservation treatments performed in blind eyes only:
- Enucleation
- Evisceration and prosthesis
- Intravitreal gentamicin injection
Evisceration is different than enucleation how?
Enucleation removes everything, while evisceration removes all contents except the sclera and cornea.
T/F: Evisceration and prosthesis may cause more pain for 2 weeks post op compared to enucleation.
True
Intravitreal gentamicin injection only works about __% of the time.
80
Side effects of intravitreal gentamicin injection:
Phthisis bulbi (eye shrinks)
Cataract development
What is the most common type of glaucoma in cats?
Secondary (neoplasia, uveitis, aqueous misdirection syndrome)
What is the first-line therapy in cats with glaucoma?
CAIs by themsevles
