Glaucoma Flashcards
What is Glaucoma?
Diverse group of diseases which all have an IOP too high for the optic nerve to function properly resulting in the loss of some or all vision
How is Intraocular Pressure maintained?
- Generated by aqueous humor production and outflow in balance
Why is IOP elevated in glaucoma
Decreased outflow! - not overproduction
How is Glaucoma diagnosed?
- Signalment, history, clinical signs
- Menace responses, cotton ball tracking, and maze testing to assess vision
- PLRs and dazzle reflexes to assess visual pathway
- Ophthalmoscopy
- Tonometry (normal 15-25 mmHg)
- Gonioscopy (referral procedure)
What breeds are commonly affected by Primary glacoma?
- American Cocker Spaniel
- Basset Hound
- Chow Chow
- Shar-Pei
- Boston Terrier
- Fox Terrier, Wire Terrier
- Norwegian Elkhound
- Siberian Husky
What are the clinical signs of glaucoma?
- Red eye (episcleral injection)
- Corneal edema
- Mydriasis
- Lens subluxation/luxation
- Painful (blepharospasm)
- Buphthalmia (enlargement of eyeball)
- Retinal and Optiv Nerve changes
- Decreased vision
How is Glaucoma diagnosed?
- Tonometry:
- Ideally both eyes should have roughly the same IOP
- >5mmHg (or >20%) difference should make you wonder why
- Ideally both eyes should have roughly the same IOP
- Gonioscopy
- special lens to visualize the iridocorneal angle
What things can affect IOP for Glaucoma diagnostics?
- Normal Diurnal variation (highest in morning)
- 2-4 mmHg change in normal dog
- Sedative, tranquilizers, and anesthetic drugs can lower IOP
- ketamine may increase IOP
- Patient cooperation
- minimize pressure applied on eyelids and neck
What is Primary Glaucoma?
- Breed related
- Always bilateral
- “good” eye will be lost in median for 8mo
- With prophylactic therapy - median time to onset of glaucoma is 31mo
What are causes of Secondary Glaucoma?
- Anterior lens luxation
- Anterior uveitis
- Neoplasia
- Hyphema
What determines if Glaucoma is Acute or Chronic?
- Acute - less than 24 hrs old
- Chronic - >24hrs old
- Buphthalmia (Big, Blue = Blind)
What are the goals of Glaucoma Therapy
- Save or regain, and maintain vision
- Achieve and maintain comfort
- Control Intraocular Pressure
- target “safe” level
- avoid progressive optic nerve and retinal damage w/ associated visual deficits
What is the Treatment for Acute Glaucoma?
- Emergency treatment:
- Topical prostaglandin analogues
- latanoprost 0.005%
- Travaprost 0.004%
- Topical carbonic anhydrase inhibitors
- Dorzolamide 2%
- Brinzolamide 1%
- Beta blocker
- Timolol 0.5 & 0.25%
- Betaxolol 0.5%
- Hyperosmotic agents
- Dehydrate vitreous
- Lasts ~6-10hrs
- IV mannitol 1-2 g/kg
- slowly over 20-30min
- Glycerin 1-2 g/kg PO
- may produce emesis
- Withhold water for 4 hrs
- Topical prostaglandin analogues
- Maintenance therapy:
- Latanoprost 0.005% SID to BID
- Dorzolamide 2% TID to QID
- Timolol 0.5% BID
- Treatment of “normal” eye
- Timolol 0.5% BID
- Frequent IOP checks of both eyes
What are the counterindications for hyperosmotic agents as treatment for acute glaucoma
- Renal disease
- Cardiovascular disease
- Dehydration
- Diabetes (glycerin)
- Other debilitating disease
What are signs of Chronic Glaucoma?
- Irreversibly blind (duration >72hrs)
- Buphthalmic
- except puppies
- Absent dazzle reflex
- Absent consensual PLR to fellow eye
What is the treatment for Chronic Glaucoma?
- Enucleation
- Evisceration
- Chemical ablation
What glaucoma medications are there?
- Topical Prostaglandin derivatives
- PGF2a derivatives
- Carbonic anhydrase inhibitors
- Sympatholytic agents (adrenergic antagonists) Beta blockers
- Cholinergic miotics
What PGF2a derivatives are used to treat Glaucoma?
- Latanaprost 0.005%
- Travoprost 0.004%
- Increase uveoscleral outflow
- Species specific
- Causes miosis but does not lower IOP in cats
- Ineffective in horses
- Use SID or BID
What Carbonic anhydrase inhibitors are used for Glaucoma treatment?
- Dorzolamide 2%
- Brinzolamide 1%
- TID to QID treatment
- Decrease aqueous humor production
- May be topically irritating
- dorzo pH 5.6 vs brinzo pH 7.5
- Oral CAI rarely used due to systemic side effects
What are the Sympatholytic agents used for Glaucoma treatment?
- 0.25% & 0.5% Timolol (B1 & B2), Betaxolol (B1)
- BID
- Inhibits B receptors on ciliary epithelium
- Decrease aqueous humor production
- may also increase aqueous humor outflow
- Mild miosis
- Potential adverse effects
- Bradycardia
- Exacerbation of asthma in cats
- Mild decrease in tear production
What Cholinergic miotics are used for Glaucoma Treatment
- Direct-acting parasympathomimetic agent
- 2% pilocarpine
- Indirect-acting parasympathomimetic agent
- 0.25% or 0.125% demecarium bromide (compounded)
- increase aqueous humor outflow
- Usually not effective alone
- Contraindicated in uveitis and anterior lens luxation
- Topical pilocarprine - very irritating
- Demecarium bromide for prophylactic therapy SID
- often administered with topical steroid SID
How are the underlying problems of Glaucoma treated?
- Lens luxation - refer for surgery if still visual
- Uveitis - treat the inflammation
- Intraocular neoplasia - enucleation?
- Hyphema - determine cause
What are the surgical options for increasing outflow of aqueous humor?
- Gonioimplants:
- Tube in AC drains fluid to subconjunctival space
- Fibrosis leads to early failure (high rates)
- Filtering procedures:
- Creating holes in iris, sclera, ciliary body
- Low success rate in veterinary patients
What are the surgical options to decrease Aqueous Humor Production?
- Destruction of ciliary body
- Cyclophotocoagulation-diode or YAG laser
- Transcleral
- Endolaser
- Cyclophotocoagulation-diode or YAG laser
- Both-postoperative pressure spike, cataract formation, inflammation
- Can perform both cyclophotocoagulation and gonioimplant at the same time increases “success” rate to 58% visual in 1 year
