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.

2. Classification

Primary

 Anatomical abnormality of iridocorneal angle

 Many purebreds

 Rarely bilateral at onset but contralateral usually follows first eye sometime later

Secondary

Another disease is the initiating cause:

 Uveitis

 Trauma

 Uveodermatologic syndrome

 Intraocular neoplasia

 Lens luxation

 Hyphema

3. Diagnosis

Clinical signs:

 Episcleral injection

 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

 Schiotz

 Must be vertical

 Need three people to operate--one to hold the dog, one to hold the head and one to operate the device

 TonoPen

 Accurate, but not error-proof

 Watch for blinking (will raise IOP 10 mmHg)

 Keep fingers off eyelids (use bony rim of orbit)

 Loosen collar

 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

Acute Glaucoma

 Blepharospasm

 Partial prolapse of the third eyelid

 Obviously painful--tends to "protect" the area

Chronic Glaucoma

 No blepharospasm

 Lens subluxation

 Buphthalmos

 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

6. Treatment

1.  Preserve vision

2.  Control pain

3.  Delay onset of glaucoma in fellow eye (primary glaucomas)

Preserving Vision

 Only possible with acute glaucoma

 If IOP > 40 mmHg for more than 24 hours, irreversible optic nerve and retinal damage will result

Acute Glaucoma

1.  Administer emergency medical treatment to restore vision

2.  Referral for laser cycloablation as soon as possible

Note: Acute glaucoma = Potentially visual eye

Chronic Glaucoma

1.  Start medical treatment to decrease discomfort

2.  Pursue surgical options for long term control

Hyperosmotics

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

Emergency Treatment

Miotics

 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.

Prostaglandin Analogue

 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

Recommended Protocol

 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

 Cyclocryotherapy

Laser Cyclophotocoagulation

Transcleral Application

 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%)

 Complications:

 Hemorrhage

 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%

Intraocular Application

 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!

Enucleation

Evisceration and Intraocular Prosthesis

 Cosmetic

 Natural movement

 Minimal complications

Chemical Cycloablation

Intravitreal gentamicin sulphate injection:

 Economical

 Outcome variable

 Procedure:

 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)

Primary Glaucomas

 Do not forget the other eye! Average time of onset of glaucoma in contralateral eye is one year

Prophylactic Therapy

 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

Drugs

 Factors to consider:

 Ease of administration

 Cost

 Demecarium bromide (Humorsol) 0.25%

 Miotic

 Given sid. at bedtime

 Often need to use with steroid sid.

 Compounded drug

 Other drugs:

 Timolol 0.5%--bid

 Methazolamide--2 mg/kg po bid

 Xalatan--expensive--keep for emergency

Key Points

 Refer early if visual

 Gonioscopy of contralateral eye recommended in primary glaucoma

 Buphthalmic globes are painful

 Prophylactic therapy for fellow eye in primary glaucomas

 Client education

 Realize this is a difficult disease to treat overall!