Glaucoma Flashcards
Glaucoma is
a group of eye diseases which result in damage to the optic nerve and vision loss due to elevation of intraocular pressure due to inadequate drainage of aqueous humor.
Primary glaucoma (hereditary) is most common in dogs, less common in cats. Cats tend to get secondary glaucoma more (e.g. FIV induced chronic uveitis leading to glaucoma, or trauma induced glaucoma).
Results in blindness, pain and high intraocular pressure, which is eventually unresponsive to medication.
Aqueous humor contains nutrients and oxygen that are used by the structures within the eye. The excess fluid is constantly drained from the eye between the cornea and the iris - area is called the iridocorneal angle or the filtration and drainage angle.
Normal IOP?
Normal diff between eyes?
Vision loss when IOP:
≥ ? mmHg in dogs,
≥ ? mmHg in cats
If IOP > ? mmHg for more than 24 h you get irreversible optic nerve and retina damage.
Normal IOP 8-30 mmHg
Normal diff between eyes ≤ 8 mmHg
Vision loss when IOP:
≥ 25 mmHg in dogs,
≥ 31 mmHg in cats
If IOP > 40 mmHg for more than 24 h you get irreversible optic nerve and retina damage.
Gonioscopy is
evaluation of iridocorneal drainage angle.
This area is crucial for drainage of aqueous humor, and its assessment helps in diagnosing conditions like glaucoma.
During gonioscopy, a special lens is placed on the eye to visualize the angle structures, such as the trabecular meshwork, scleral spur, and iris.
It provides valuable information about the openness of the angle and any abnormalities, helping to assess the risk of glaucoma.
Pectinate ligaments do what?
hold the iridocorneal angle open.
Degeneration of these ligaments causes shortening of them and thus narrowing or closing of the angle (goniodysgenesis).
When narrowed or closed, prevents the drainage of aqueous humor.
goniodysgenesis =
Goniodysgenesis refers to a congenital condition where the development of the eye’s anterior chamber angle is abnormal.
In goniodysgenesis, the trabecular meshwork, which plays a role in filtering the aqueous humor, may be malformed or underdeveloped. The condition can be present at birth and is often hereditary. It’s one of the leading causes of glaucoma.
Management typically involves monitoring intraocular pressure and some type of intervention to slow or manage disease progression.
In which species can you view the iridocorneal angle without a gonioscope?
In cats, its visible.
To see it in dogs, you need a gonioscope lens.
Primary glaucoma occurs due to
inherited anatomical abnormalities in the drainage angle.
For example, in narrow angle glaucoma there is a shallow anterior chamber which causes the iris to block the iridocorneal angle interfering with the filtration.
Abnormalities in the drainage angle (goniodysgenesis) can lead to a raised IOP in middle age and eventual glaucoma.
Breeds Associated with Glaucoma. (hint: LOADS)
Akita
Dalmatian
Norwegian elkhound
Alaskan malamute
Husky
All of Spaniels
Poodle
Samoyed
Basset hound
Flat-coated Retriever
Shar Pei
Beagle
Giant schnauzer
…….Shih tzu, Boston terrier, Great Dane, Bouvier des flandres, Greyhound, Smooth haired fox terrier, Bull mastif, Italian greyhound, Chow chow, Miniature pinscher, Wirehaired fox terrier, Miniature schnauzer…….
Causes of Secondary glaucoma. (5)
- Uveitis (inflammation of the interior of the eye) or severe intra-ocular infections, resulting in debris and scar tissue blocking the drainage angle.
- Anterior dislocation of the lens meaning the lens falls forward and physically blocks the drainage angle or pupil so that fluid is trapped behind the dislocated
lens. - Tumors can cause physical blockage of the iridocorneal angle.
- Intra-ocular bleeding, the blood clot can prevent drainage of the aqueous humor.
- Damage to the lens: lens proteins leaking into the eye as a result of a ruptured lens can cause an inflammatory reaction, which results in swelling
and blockage of the drainage angle.
Results in increased intra-ocular pressure due to disease or injury to the eye.
Describe primary open angle glaucoma.
Primary open-angle glaucoma is a progressive, chronic eye condition characterized by an increase in intraocular pressure due to impaired drainage of aqueous humor through the trabecular meshwork and Schlemm’s canal.
Unlike other types of glaucoma, the angle between the iris and cornea remains open in POAG, but the drainage system is dysfunctional. In POAG, the trabecular meshwork either becomes less efficient or more resistant to aqueous humor flow.
The cause of this dysfunction is often not well understood but is believed to involve genetic factors, structural abnormalities in the eye, and possibly inflammation, all of which contribute to the impaired drainage process.
What sedative can increase IOP?
ketamine
In a normal eye, aqueous humor is produced by the ciliary body, circulates through the anterior chamber, and drains through…
the trabecular meshwork into Schlemm’s canal.
Secondary glaucoma caused by uveitis, how exactly?
iridocorneal angle occlusion by fibrin, blood clot or inflammatory cells
or,
angle occlusion by dislocated iris or lens (iris bombe, lens luxation).
Contraindication for mydriatics?
glaucoma!
don’t use atropine in glaucoma cases because it can increase intraocular pressure.
In individuals with glaucoma, especially those with narrow or closed-angle glaucoma, the dilation of the pupil can cause the iris to shift forward, potentially blocking the drainage angle between the cornea and iris.
This can worsen the outflow of aqueous humor and lead to a dangerous increase in intraocular pressure, exacerbating the condition and possibly causing permanent optic nerve damage. Therefore, atropine is generally contraindicated in patients with glaucoma.
Describe Acute glaucoma. (5)
- We see/recognize this very rarely.
- In all patient with blepharospasm, redness of eye, epiphora, blindness - you must check intraocular pressure.
- Typically hyperemia in glaucoma: conjunctival episcleral blood vessels congestion.
- Mydriasis may be present – large, slowly responsive or unresponsive to light pupil.
- Edema in the dog cornea, because the endothelium is damaged. In cats, typically no edema.
Main diff to chronic is that chronic sees buphthalmos - otherwise same signs.
Describe chronic glaucoma. (4)
- Typically hyperemia in glaucoma – conjunctival episcleral blood vessels congestion.
- Mydriasis – large, unresposive pupil.
- Enlargement of the eyeball – buphthalmos.
- Edema in the dog cornea, because the endothelium is damaged. In cats, typically no edema.
- Chronic glaucoma causes chronic pain and its often underestimated because we don`t see blepharospasm in chronic. The Pain is like a migraine headache.
- Symptoms tend to be more subtle: sleeping more, decreased activity, grumpy, decreased appetite, occasionally “head shy”. Think “old-age” symptoms.
- Only after removing the eye, does the dog become more happy, plays, we can understand how much pain caused glaucoma.
Main diff to acute is that chronic sees buphthalmos - otherwise same signs.
iris color changes happen due to chronic uveitis. this cat has unilateral, left-sided glaucoma secondary to chronic uveitis. (and the chronic uveitis may be due to some infectious disease such as FIV etc.)
chronic Glaucoma with typical episcleral hyperemia/congestion and corneal edema
corneal striae are
Also called Haab’s striae, are curvilinear breaks in Descemet’s membrane with stromal edema, resulting from acute stretching of the cornea in primary congenital glaucoma.
Describe treatment of acute glaucoma.
- Acute glaucoma is an emergency.
- You can potentially Preserve vision but only with acute glaucoma.
- Control pain!
- Delay onset of glaucoma in contralateral eye (primary glaucoma).
- Administer emergency medical treatment to restore vision.
- Referral for laser cycloablation as soon as possible.
mannitol, miotics, carbonic anhydrase inhibitors (decrease IOP), prostaglandin analogues (e.g. latanoprost causes pupil constriction)
Describe treatment of chronic glaucoma.
- Start medical treatment to decrease discomfort.
- Pursue surgical options for long term control.
timolol (reduces IOP), latanoprost is a prostaglandin analogue (induces miosis), demecarium bromide (decrease IOP)
Describe hyperosmotics for the treatment of glaucoma.
Mannitol reduces the fluid in the vitreous humor body, it doesn’t actually affect the aqueous humor flow.
Mannitol 1-1.5 gm/kg (7.5 ml of 20% solution) IV over 15-20 min.; repeat if necessary in 12 hours.
a. Withhold water for at least 4-6 hours, then slowly reintroduce.
b. You Can use mannitol with diabetics.
c. NB May be contraindicated in glaucomas secondary to uveitis.
Describe miotics for the treatment of glaucoma.
Miotics Help to open up the iridocorneal angle.
- NB Can exacerbate uveitis (avoid with secondary glaucomas).
- Avoid with anterior lens luxations
- Pilocarpine (2%) (cholinergic agonist) can be used but needs to be given every 5 minutes until pupil constricts. Not ideal long-term.
Describe carbonic anhydrase inhibitors for the treatment of glaucoma.
For the reduction of intraocular pressure (IOP), CAIs inactivate carbonic anhydrase and interfere with the sodium pump, which decreases aqueous humor formation and thus lowers IOP.
- Methazolamide 2-4 mg/kg PO every 8-12 hours
- Indicated for Primary or secondary glaucoma
Topical carbonic anhydrase inhibitors:
* Trusopt® or Azopt ® (dorzolamide) give t.i.d.
* Cosopt® (dorzolamide + timolol), give b.i.d. to t.i.d. NB Beware in old dogs with heart disease.
Describe prostaglandin analogues for the treatment of glaucoma.
used to treat glaucoma by constricting the pupil thus increasing the outflow of aqueous humor, thereby lowering intraocular pressure.
- Xalatan® (latanoprost) or Travatan® (travoprost)–powerful topical drugs. Rapidly decrease IOP.
- Mechanism of action: increase uveoscleral outflow.
- Cause intense miosis.
- Give 1 drop b.i.d.
- Can work just as well as mannitol in some cases
- Avoid with anterior lens luxations.
- Can exacerbate uveitis (avoid with secondary glaucomas).
- Avoid in cats.
Emergency Treatment of Acute Glaucoma
Recommended Protocol (by Andrew Turner All Animal Eye Services Mount Waverley, Victoria, Australia)
- Mannitol 1 gm/kg IV over 20 min
- Methazolamide 2-4 mg/kg PO (carbonic anhydrase inhibitor decrease aqueous humor formation and thus lowers IOP.)
- Miotic such as latanoprost or travoprost is ideal, otherwise use pilocarpine.
Check IOP 1-2 hours after mannitol and then again the next day (12-24 hours later).
You may use miotics and methazolamide without mannitol, but check IOP 1-2 hours later to see if you need to change your treatment plan.
- Return of vision may be immediate or take several days (as long as IOP remains normal).
- If vision does return: refer to ophthalmologist!
Glaucoma is a surgical disease meaning…
surgery is the treatment of choice for eyes that are still visual after an acute glaucoma attack.
Surgery Destroys a portion of the ciliary body to permanently decrease aqueous production and is Used in combination with continued medical therapy.
- Cycloablation/ cyclocryotherapy/ cyclocoagulation
Long term success of IOP control without surgery = 0%.
Chance of vision loss after laser surgery/ cyclocryotherapy/cyclocoagulation = 20-25%.
Chance of vision loss with medical therapy alone = 100%.
define trabeculectomy for glaucoma
Trabeculectomy is a surgical procedure used to treat glaucoma by creating a new drainage channel in the eye to lower intraocular pressure. This helps prevent optic nerve damage and vision loss by allowing excess aqueous humor to drain more efficiently.
Ocular Evisceration and intrascleral prothesis in small animals.
Ocular evisceration in small animals involves the removal of intraocular contents while preserving the scleral shell. An intrascleral prosthesis is then implanted within the remaining sclera to maintain cosmetic appearance and orbital integrity, commonly performed in cases of severe ocular disease or trauma.
- Cosmetic
- Natural movement is retained
- Minimal complications
Describe Prophylactic Therapy for primary glaucoma.
Do not forget the other eye! Average time of onset of glaucoma in contralateral eye is one year. So, starting prophylactic tx Delays onset of glaucoma in fellow eye. Also, Makes client look at the eye daily.
Monitor for changes regularly (measure IOP every 2-4 months). Client education; They Need to know what to do when signs occur in the 2nd eye.
Drugs used for glaucoma prophylaxis:
* Timolol 0.5%
* Xalatan (latanoprost), lowers IOP
* Demecarium bromide (Humorsol) 0.25% (parasympathomimetic drug that acts as an acetylcholinesterase inhibitor and decreases IOP)
If you see a patient in general practice and you suspect glaucoma but have no access to IOP measurement what can you prescribe to relieve their signs while referring to ophtho?
prescribe a topical carbonic anhydrase inhibitor as they’re quite safe. They decrease aqueous humor formation and thus lowers IOP.
e.g. Azopt
can cause salivation espesh in cats
