Glaucoma

Question 1

What is Glaucoma?

Answer 1

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

Question 2

How is Intraocular Pressure maintained?

Answer 2

• Generated by aqueous humor production and outflow in balance

Question 3

Why is IOP elevated in glaucoma

Answer 3

Decreased outflow! - not overproduction

Question 4

How is Glaucoma diagnosed?

Answer 4

• 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)

Question 5

What breeds are commonly affected by Primary glacoma?

Answer 5

• American Cocker Spaniel
• Basset Hound
• Chow Chow
• Shar-Pei
• Boston Terrier
• Fox Terrier, Wire Terrier
• Norwegian Elkhound
• Siberian Husky

Question 6

What are the clinical signs of glaucoma?

Answer 6

• Red eye (episcleral injection)
• Corneal edema
• Mydriasis
• Lens subluxation/luxation
• Painful (blepharospasm)
• Buphthalmia (enlargement of eyeball)
• Retinal and Optiv Nerve changes
• Decreased vision

Question 7

How is Glaucoma diagnosed?

Answer 7

• Tonometry:
  
  • Ideally both eyes should have roughly the same IOP
    
    • >5mmHg (or >20%) difference should make you wonder why
• Gonioscopy
  
  • special lens to visualize the iridocorneal angle

Question 8

What things can affect IOP for Glaucoma diagnostics?

Answer 8

• 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

Question 9

What is Primary Glaucoma?

Answer 9

• Breed related
• Always bilateral
• “good” eye will be lost in median for 8mo
  
  • With prophylactic therapy - median time to onset of glaucoma is 31mo

Question 10

What are causes of Secondary Glaucoma?

Answer 10

• Anterior lens luxation
• Anterior uveitis
• Neoplasia
• Hyphema

Question 11

What determines if Glaucoma is Acute or Chronic?

Answer 11

• Acute - less than 24 hrs old
• Chronic - >24hrs old
  
  • Buphthalmia (Big, Blue = Blind)

Question 12

What are the goals of Glaucoma Therapy

Answer 12

• 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

Question 13

What is the Treatment for Acute Glaucoma?

Answer 13

• 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
• 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

Question 14

What are the counterindications for hyperosmotic agents as treatment for acute glaucoma

Answer 14

• Renal disease
• Cardiovascular disease
• Dehydration
• Diabetes (glycerin)
• Other debilitating disease

Question 15

What are signs of Chronic Glaucoma?

Answer 15

• Irreversibly blind (duration >72hrs)
• Buphthalmic
  
  • except puppies
• Absent dazzle reflex
• Absent consensual PLR to fellow eye

Question 16

What is the treatment for Chronic Glaucoma?

Answer 16

• Enucleation
• Evisceration
• Chemical ablation

Question 17

What glaucoma medications are there?

Answer 17

• Topical Prostaglandin derivatives
• PGF2a derivatives
• Carbonic anhydrase inhibitors
• Sympatholytic agents (adrenergic antagonists) Beta blockers
• Cholinergic miotics

Question 18

What PGF2a derivatives are used to treat Glaucoma?

Answer 18

• 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

Question 19

What Carbonic anhydrase inhibitors are used for Glaucoma treatment?

Answer 19

• 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

Question 20

What are the Sympatholytic agents used for Glaucoma treatment?

Answer 20

• 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

Question 21

What Cholinergic miotics are used for Glaucoma Treatment

Answer 21

• 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

Question 22

How are the underlying problems of Glaucoma treated?

Answer 22

• Lens luxation - refer for surgery if still visual
• Uveitis - treat the inflammation
• Intraocular neoplasia - enucleation?
• Hyphema - determine cause

Question 23

What are the surgical options for increasing outflow of aqueous humor?

Answer 23

• 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

Question 24

What are the surgical options to decrease Aqueous Humor Production?

Answer 24

• Destruction of ciliary body
  
  • Cyclophotocoagulation-diode or YAG laser
    
    • Transcleral
    • Endolaser
• 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