Glaucoma Flashcards
Glaucoma
Increased intraocular pressure causing damage to optic nerve and retina
Normal IOP dog
10-20 mmHg
How close should the IOPs of two different eyes be?
- Within 5 mmHg
Cat and horse IOP normal
12-30 mmHg
- Not hard and fast for them
Flow of aqueous in the eye (3 steps)
- Aqueous produced by ciliary body
- Passes through the pupil into the anterior chamber
- Exits the eye through the iridocorneal angle
WHat determines IOP?
- Volume of aqueous
Can IOP ever be high due to over-production of aqueous?
- No, we say never
When does intraocular pressure increase?
- WHen aqueous cannot escape the eye through the ICA
- i.e. the ICA is closed
What are the two categories of causes of glaucoma?
- Primary glaucoma (hereditary)
- Secondary glaucoma (other ocular disease)
Who gets hereditary/primary glaucoma?
- Cocker SPaniels
- Siberian husky
- Bassett hound
- Many others
Age of onset with hereditary glaucoma
- Any age
- As young as 2 years of age in huskies
Secondary glaucoma causes
- Lens induced uveitis, instability, luxation
- Uveitis any cause
- Neoplasia (ocular or metastatic)
Most common cause of secondary glaucoma?
- Cataracts –> LIU –> glaucoma
Mechanism of secondary glaucoma
- Inflammatory cells, blood, or tumor cells in ICA
- Pre-iridial fibrovascular membrane from uveitis or retinal detachment covers the ICA
- Peripheral anterior synechia
How can anterior lens luxation lead to glaucoma?
- Pressure increase due to physical obstruction, disturbance of intraocular environment, and/or induction of uveitis
How does diabetic cataracts lead to glaucoma?
- Intumescent lens can push iris forward against the cornea and close the ICA
- Or lens induced uveitis from lens proteins
Acute glaucoma - how quickly should yo utreat?
- Emergency to save vision
Signs of acute glaucoma
- Corneal edema (not as much in cats)
- Dilated, sluggish pupil
- Decreased/absent menace
- Pain/epiphora/blepharospasm
- Episcleral vessel congestion
Mechanism of corneal edema acute glaucoma
- High IOP causes endothelial cells to be paralyzed and can’t pump fluid out –> corneal edema
Why is the pupil dilated in glaucoma?
- Pressure is high enough to paralyze pupil –> dilated
Main features to distinguish glaucoma from uveitis
- High IOP - dilated pupil
Heelers and glaucoma
- Tend to get high pressures but not corneal edema with glaucoma
How do you diagnose IOP?
- Tonovet pen
Treatment of acute glaucoma principles
- Rapidly decrease IOP
- Neuroprotection (optic nerve - can get damaged with reperfusion injury)
- Treat primary problem if secondary glaucoma
- Primary glaucoma usually presents with blind eye- treat fellow eye preventatively
What is the mainstay to decrease IOP with glaucoma?
- Dorzolamide/timolol
Dorzolamide/timolol MOA
- Carbonic anhydrase inhibitor (slows production of aqueous)
- Beta blocker (vasoconstriction to decrease aqueous production)
Which species can you use dorzolamide/timolol on?
- Dogs, cats, horses
What can you use dorzolamide/timolol to treat?
- Primary glaucoma
- Lens luxation
- Uveitis
Caution for dorzolamide/timolol
- Asthmatic cats
Mannitol MOA
- Osmotic diuresis to dehydrate the eye
When to use mannitol?
- If IOP >40 mmHg
- Primary glaucoma only
How to use mannitol?
- IV slowly over 15-30 minutes
- Give once
- WIthhold water and fluids for 4 hours
Contraindications for mannitol?
- Uveitis
- If eye is inflamed, mannitol goes into vitreous and draws fluid in which is bad
Latanoprost MOA
- Synthetic prostaglandin
- Decreases aqueous production
- Increases uveoscleral outflow
- Either decreases IOP in 20 min or doesn’t work for that patient
- Maximal effect in 1 hour
Species for latanoprost
- DOGS ONLY
- Not cats or horses
Contraindications for latanoprost
- Uveitis or anterior lens luxation (traps vitreous in pupil)
Who can use latanoprost?
- ONLY opthalmologists
Solu-medrol and solu-delta purpose
- Prevent reperfusion injury
Solumedrol and solu-delta MOA
- Calcium channel blocker to stop cytotoxic effects of ischemia
- Like amlodipine but IV
Prognosis for glaucoma
- Always grave
Treatment for glaucoma
- Surgical procedure when medical therapy fails
- Surgical procedures are not successful long term (micropulse, valve implant, diode laser cyclophotocoagulation, etc.)
- May preserve vision in the short term
- Very expensive medical treatment, with lots of drugs
- Long term medical treatment will not be effective
Secondary glaucoma treatment principles
- MUST treat the underlying problem
- Generally associated with uveitis
Drug of choice for secondary glaucoma
- Dorzolamide/timolol is the drug of choice
Chronic glaucoma urgency
- Not an emergency to lower pressure, as the eye is already blind
How to know when looking at the eye if it’s secondary or primary glaucoma?
- I guess you’re looking for signs of uveitis or something else going on
- Flare, swollen iris, synechia
Signs of chronic glaucoma
- Corneal edema
- Dilated pupil with absent PLR
- Absent menace
- Pain
- Episcleral injection
- Corneal striae (breaks in Descemet’s)
- Retinal degeneration (hyperreflectivity)
- Cupped optic disc (lost myelin and vessels)
- BUphthalmic - enlarged globe
Process of glaucoma and blindness
- Pressure destroys ganglion –> lose optic nerve –> retinal degeneration –> ruined corneal endothelium –> corneal edema –> painful eye
Medical management for chronic glaucoma
- Not appropriate in a blind, painful eye
Options for a blind, painful eye
- Enucleation
- Enucleation with an implant (not for cats)
- Evisceration with prosthesis
- Chemical cytoablation
What is the best treatment for a blind, painful eye?
- Enucleation
Why not put an implant in the socket for cats?
- They get cancer
Contraindication for evisceration with prosthesis?
- Not for intraocular tumor or corneal disease
Contraindication for chemical cytoablation
- Not for cats or anyone you like
- Associated with secondary ocular neoplasia (traumatic sarcoma)
Description of chemical cytoablation
- Aspirate fluid from vitreous, avoid the lens, inject gentocin and dexamethasone intravitreally
- must manage post-op uveitis and pressure
- Multiple treatments may be needed
Issues with cytoablation
- Persistently increased IOP
- Ocular neoplasia may develop
- LIU
Feline glaucoma causes
- Usually secondary to uveitis, lens luxation, neoplasia, trauma, senile change
- Primary reported in Siamese cats
- Ultimately fluid goes into the vitreous and pushes the iris and lens forward
Treatment for feline glaucoma
- Requires removal of the lens
- Referral procedure
Prognosis for feline glaucoma
- Grave
- You always lose
Treatments to reduce pressures in cats
- Dorzolamide/timolol
- Do not use timolol in asthmatic cats
- Latanoprost not useful
- Usually no point
Microphthalmia
- Congenitally small globe - may or may not be visual
Who gets traumatic proptosis most often?
- Brachycephalic dogs, Pekingese
- Definition of proptosis
- Eyelids are trapped behind the globe
How quickly to correct traumatic proptosis?
- Very quickly
- Prior to referral
Treatment for traumatic proptosis
- Replace the globe
- Warm compress, systemic and topical antibiotics
- Oral anti-inflammatory
- 14-21 day suture removal when globe retropulses
How to replace the globe with traumatic proptosis?
- Anesthesia, lubricate, protect cornea
- Stain cornea to make sure there’s no ulcer
- Lateral canthotomy
- Flat scalpel handle across cornea
- Place mattress sutures
- Strabismus hook to lift lids
- Temporary tarsorrhaphy
Tarsorrhaphy
- Pre place sutures
- Go through rubber band and through Meibomian gland
- Tie them
- Close the eyelids
- Can leave a little open at the medial canthus
Potential complications of proptosis?
- Blindness, exophthalmos, lagophthalmos, ulceration
- Lateral deviation of the globe
Follow up care for proptosis
- Put an E-collar on
- Check in a few days because the suture will loosen up and don’t want it rubbing on the cornea
- Usually she leaves for a couple of weeks
Proptosis in dogs that are dolichocephalic - prognosis
- Worse than in brachycephalic dogs
- Enucleation is the best choice
Prognosis for proptosis in cats
- Poor prognosis
Prognosis for proptosis in horses or any species with a closed bony orbit
- Poor
Other indications of poor prognosis
- Hyphema
- Soft globe
- 2 orbital muscles ruptured (medial rectus ruptures first)
- No direct or consensual PLR
Pthisical eyes
- Clinically, it is characterized by a soft atrophic eye with disorganization of intraocular structures.
Exophthalmosis vs proptosis vs buphthalmos
- Make sure you can distinguish
Some characteristics of exophthalmos
- Third eyelid is up
- Mass effect in orbit and globe is pushed out
Differentials for exophthalmos
- Inflammation
- Cellulitis
- Neoplasia
- Hemorrhage
Orbital cellulitis causes
- Peridontal disease (abscess)
- Penetrating foreign body
- Unknown etiology
Treatment of periorbital cellulitis
- Localize with oral exam
- Ultrasound, MRI
- Remove abscessed teeth
- Remove FB
- Systemic antibiotics
- Systemic NSAIDs
- Topical antibiotics
- Surgical drainage only if US guided
