Glaucoma Case 1 Flashcards
What is a direct PLR?
when the pupil of the eye you’re shining light into constricts
What is a consensual PLR?
when the pupil of the eye opposite of the one you’re shining light into also constricts
What can cause a patient to have a negative consensual OD and negative direct OS when testing PLR?
damage to optic nerve
What can cause a patient to have a negative consensual PLR?
If IOP is elevated enough, the iris sphincter muscle undergoes ischemic necrosis which results in inability of pupil to constrict
T/F: vision can be almost completely gone and dog can still have positive menace response
True - dog does not have to have good vision to have a menace response!
What is the normal range of IOP in dogs?
8-18 mmHg
What is tonometry?
measurement of intraocular pressure
What are the 3 modes of measuring IOP in vet med?
1) TonoPen (applanation)
2) Schiotz tonometer (indentation)
3) TonoVet (rebound)
How does a TonoPen work?
Tip of tonopen is tapped against corneal surface, area of cornea equal to tip surface is flattened (applanated), and IOP is calculated from the measurement of how hard you are pushing the tonometer to flatten the surface area
How does indentation tonometry work?
Schiotz tonometer places known weight on central cornea and measures how deeply the weight indents the cornea. The harder the eyeball, the less indented by the weight. IOP read off calibration table.
How does rebound tonometry work?
TonoVet has small plastic rod with spherical tip is “thrown” by the instrument at the cornea, bounces back into instrument, and the harder the eyeball is the faster the rod bounces back. Instrument internally calculates IOP based on the “bounce back speed”.
Which mode of measuring IOP does not require topical anesthetic?
Rebound tonometry with TonoVet
Why are dogs with elevated IOP blepharospastic?
Painful! The discomfort associated with elevated IOP is more a reflection of how rapidly the pressure has gone up, not necessarily correlating to the value of the IOP
What are the 2 clinical manifestations of hyperemia (redness of the whites of the eyes)?
Episcleral injection and conjunctival injection
What does conjunctival injection indicate?
Superficial ocular disease, like
- conjunctivitis, KCS, distichia, etc
What does episcleral injection indicate?
Intraocular disease - usually either glaucoma or anterior uveitis
Why is the normal cornea clear?
Relative dehydration, avascularity, lack of pigment, non-keratinized nature of epithelium, organized arrangement of collagen fibrils
What causes corneal edema?
1) elevated IOP provides greater hydrostatic pressure to drive fluid into stroma at greater than normal rate
2) the elevated IOP damages the endothelial cells, thus decreasing their pump function
What causes mydriasis (dilation of the pupil)?
combination of optic nerve damage (results in poor direct PLR) and ischemic necrosis of iris sphincter muscle (results in poor consensual PLR)
What is gonioscopy?
“to look at the angle” (iridocorneal angle)
How does gonioscopy work?
A large contact lens (goniolens) is placed on cornea, which changes the functional geometry of the anterior segment, and allows light from the angle to escape the eye. Result is we have visualization of the iridocorneal angle
what is the cause of elevated IOP?
problem with aqueous outflow, leading to a drainage issue at the iridocorneal angle
What is goniodysgenesis?
“malformed angle”
What is the main microscopic structure affected with goniodysgenesis?
The pectinate ligaments do not form properly and are replaced by a solid sheet of tissue
In normal dogs, embryonically the pectinate ligaments start as a solid sheet and then undergo the process of ______________ which leaves threadlike pectinates and large flow spaces.
Rarefaction
T/F glaucoma is a morphologic diagnosis
True
What is glaucoma?
A family of diseases characterized by optic nerve damage/degeneration that is associated with elevated IOP
After the IOP normalizes after glaucoma has begun treatment, will the optic nerve be recovered?
No, once optic nerve has felt impact of high pressure the degeneration continues even after the IOP has normalized
What is the difference between primary and secondary glaucoma?
Primary = nothing else has happened to cause the glaucoma to happen
Secondary = anytime something happens to secondarily clog the angle and causes the IOP to increase
For primary glaucoma in dogs, what is the only etiologic diagnosis?
Goniodysgenesis
What is Latanoprost?
Potent, rapid-acting IOP lowering agent
MOA of latanoprost?
Reduce aqueous production and/or increase aqueous outflow, we aren’t really sure but it most likely does both
What is Timolol?
A topical beta-blocker that is not a very potent IOP lowering agent
MOA of Timolol?
Reduces aqueous production
What is the advantage to using a beta-blocker (Timolol) in the other (normal) eye in cases of glaucoma?
Delays onset of glaucoma in the other eye for about 33 months
T/F all glaucoma is going to result in permanent blindness eventually
True
T/F primary glaucoma is always unilateral
False - primary glaucoma is ultimately bilateral
Why is it important to recheck the eye within 2 hours of prescribing glaucoma drugs?
IF at that 2 hr mark the IOP is still elevated, THEN you can take corrective action before it worsens!
We want the visual eye to stay visual and not progress to blindness!
Acute glaucoma in the potentially visual eye is considered a ….
Ophthalmic emergency
T/F Latanoprost can be used as both emergency and maintenance therapy
True
What causes a cupped optic nerve head?
Posterior depression of the optic nerve head in response to elevated pressure; cupping occurs bc of hydrostatic pressure on the nerve
What does a cupped optic nerve head indicate?
Denotes some degree of chronicity
With high IOPs that is sustained, the cupping of the optic nerve head will turn into ….
Frank optic nerve atrophy
Optic nerve atrophy appears as
small, dark, gray, avascular nerve
If optic nerve atrophy happens, the vision loss is ______
irrevocable
If all the pathology inducing elevation in IOP happens in the anterior segment, wny does the IOP go up in the region of the optic nerve too?
Pascal’s law – a pressure change occurring anywhere in a confined, incompressible fluid is transmitted throughout the fluid such that the change occurs everywhere
What is Mannitol?
An osmotic diuretic drug that works by drawing water out of the aqueous humor and vitreous humor into the intravascular space, thus shrinking the total ocular volume and reducing IOP
How is mannitol different than latanoprost?
Mannitol is given slowly IV, and is only for emergency therapy. Mannitol is a “one and done” treatment
T/F: Mannitol can be used for emergency and maintenance therapy.
FALSE - Mannitol cannot be used for maintenance therapy. Emergency drug only.
What is Dorzolamide?
A carbonic anhydrase inhibitor (which is an enzyme found in non-pigmented ciliary body epithelium that is essential for the production of aqueous humor)
MOA of dorzolamide?
Reduces production of aqueous humor
What is CoSopt?
Combination agent of timolol + dorzolamide
How does dorzolamide compare to timolol and latanoprost?
Order of potency: Latanoprost > Dorzolamide»_space;>Timolol
What is a glaucoma drainage valve?
Device that allows aqueous humor to bypass the nonfunctional iridocorneal angle
Describe how a glaucoma drainage valve works?
A tiny, hollow silicone straw with a plastic body attached is sutured directly to the sclera posterior to the limbus. A needle is used to create a tunnel into the anterior chamber and the straw is inserted through this tunnel. Aqueous can travel up the straw and onto the surface of the plastic body. The idea is for aqueous to enter systemic circulation via conjunctival vessels
What are the major problems/complications that occur with glaucoma drainage valves?
- Fibrin accumulation in the straw in early postop period
- Dense scar tissue formation around plastic body later on
What helps mitigate complications with glaucoma drainage valves post-operatively?
Anti-fibrotic medications
T/F: Glaucoma drainage valve surgery is curative
False - the surgeries always fail eventually
What is buphthalmia?
Enlarged globe
What is the only thing that causes buphthalmia?
Chronic glaucoma
By the time buphthalmia has occurred, the optic nerve has ……
Been dead a long time!
Once the globe becomes buphthalmic, what happens to the ciliary zonules?
Zonules become stretched to the breaking point resulting in subluxation of the lens
Lens luxation in this case example is
Secondary to glaucoma
When glaucoma is primary and the lens luxation is secondary, what will you see on patient presentation?
History of chronic glaucoma, eye is buphthalmic, and lens is generally still behind the iris
Once vision is not recoverable, what is the only treatment option left for a patient with glaucoma?
Enucleation
Other salvage procedures besides an enucleation are …
Evisceration with silicone prosthesis and intravitreal gentamicin injection
IF you do a gentamicin injection, what do you want to be sure of?
That the patient is already non-visual
