1. What is Glaucoma?
A group of diseases with diverse origins, resulting in an intraocular pressure that prevents nerve impulses travelling from the retina via the optic nerve to the brain. The process includes cessation of axoplasmic flow in the optic nerve, retinal ganglion cell death, loss of optic disc myelin and subsequent cupping, and visual impairment and most often blindness.
Anatomical abnormality of iridocorneal angle
Rarely bilateral at onset but contralateral usually follows first eye sometime later
Another disease is the initiating cause:
Fixed, dilated pupil
Corneal oedema (if IOP>40mmHg)
Vision loss--absent menace response
4. Confirm Clinical Diagnosis with Tonometry
Tonometry--Schiotz (indentation), TonoPen Vet (applanation), TonoVet (rebound)
Glaucoma, vision loss--IOP>25 mmHg in dogs, 31 mmHg in cats
Must be vertical
Need three people to operate--one to hold the dog, one to hold the head and one to operate the device
Accurate, but not error-proof
Watch for blinking (will raise IOP 10 mmHg)
Keep fingers off eyelids (use bony rim of orbit)
Hands off the neck--partial occlusion of jugular vein will raise IOP
Use topical anesthesia--proparacaine. May not be necessary for TonoVet.
Keep tip perpendicular to surface of cornea
5. Acute vs. Chronic
Partial prolapse of the third eyelid
Obviously painful--tends to "protect" the area
Usually no sign of ocular pain (but is painful to the animal)
It is important to differentiate an acute disease process from an "acutely noticed" one
1. Preserve vision
2. Control pain
3. Delay onset of glaucoma in fellow eye (primary glaucomas)
Only possible with acute glaucoma
If IOP > 40 mmHg for more than 24 hours, irreversible optic nerve and retinal damage will result
1. Administer emergency medical treatment to restore vision
2. Referral for laser cycloablation as soon as possible
Note: Acute glaucoma = Potentially visual eye
1. Start medical treatment to decrease discomfort
2. Pursue surgical options for long term control
1. Mannitol--1-1.5 gm/kg (7.5 ml of 20% solution) IV over 15-20 min.; repeat if necessary in 12 hours
2. Glycerin (50% solution)--1-2 ml/kg PO; can repeat in 4 hours
a. Withhold water for at least 4-6 hours, then slowly reintroduce.
b. Can use mannitol with diabetics
c. May be contraindicated in glaucomas secondary to uveitis
Helps open up the iridocorneal angle
Can exacerbate uveitis (avoid with secondary glaucomas)
Avoid with anterior lens luxations
Pilocarpine (2%)--need to give every 5 minutes until pupil constricts
Not ideal long-term
Carbonic Anhydrase Inhibitors
Methazolamide--2-4 mg/kg PO every 8-12 hours
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. Beware in old dogs with heart disease.
Xalatan® (latanoprost) or Travatan® (travoprost)--powerful topical drugs
Rapidly decreases IOP
Mechanism of action--increases uveoscleral outflow
Causes intense miosis
Give 1 drop b.i.d.
Can work just as well as mannitol in some cases
Emergency Treatment of Acute Glaucoma
Mannitol--1 gm/kg IV over 20 min.
Methazolamide 2-4 mg/kg PO
Miotic--Xalatan® or Travatan® is ideal, otherwise use pilocarpine
Check IOP 1-2 hours after mannitol and then again the next day (12-24 hours)
May use Xalatan/Travatan 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
Treatment of choice for eyes that are still visual after an acute glaucoma attack
Destroys a portion of the ciliary body to permanently decrease aqueous production
Used in combination with continued medical therapy
Immediate post-operative IOP rise often necessitates aqueous paracentesis
Or drainage device--6/0 Prolene suture--anterior chamber suture avoids IOP spike. Success rate = 70-75%
Early treatment is key
Pseudophakics have better results (95%)
Persistent ocular hypertension
Long term success of IOP control without surgery = 0%
Chance of vision loss after laser surgery= 20-25%
Chance of vision loss with medical therapy alone = 100%
Lentectomy followed by endolaser.
Efficacy presently being assessed.
Chronic Glaucoma (Irreversibly Blind Eye)
Treatment of Chronic Glaucoma
Main goal is to control discomfort
Pain like a migraine headache
Symptoms tend to be more subtle: sleeping more, decreased activity, grumpy, decreased appetite, occasionally "head shy"
Think "old-age" symptoms
All buphthalmic globes are painful and need to be treated surgically!
Evisceration and Intraocular Prosthesis
Intravitreal gentamicin sulphate injection:
25mg Gentamicin sulphate and 1 mg dexamethasone
Inject 10 mm behind limbus, enter at a 45 degree angle while aiming for optic nerve
Remove about 1 ml of liquefied vitreous before injection (use 3-way stopcock)
Do not forget the other eye! Average time of onset of glaucoma in contralateral eye is one year
Delays onset of glaucoma in fellow eye
Makes client look at the eye daily
Monitor for changes (measure IOP every 2-4 months)
Trends more important
Client education is paramount
Need to know what to do when it happens
Factors to consider:
Ease of administration
Demecarium bromide (Humorsol) 0.25%
Given sid. at bedtime
Often need to use with steroid sid.
Methazolamide--2 mg/kg po bid
Xalatan--expensive--keep for emergency
Refer early if visual
Gonioscopy of contralateral eye recommended in primary glaucoma
Buphthalmic globes are painful
Prophylactic therapy for fellow eye in primary glaucomas
Realize this is a difficult disease to treat overall!