Lecture 12 3/24/25 Flashcards
What is a direct pupillary light reflex?
when the pupil of the eye you shine a light into constricts
What is a consensual/indirect pupillary light reflex?
when the pupil of the opposite eye from which you shine a light into constricts (defined by pupil you are observing)
What can cause the direct and consensual light reflexes to be negative in potential glaucoma cases?
damage to the optic nerve due to elevated intraocular pressure
How does increased IOP lead to negative PLRs?
elevated IOP causes ischemic necrosis of the iris sphincter muscle, which results in the inability to constrict the pupil
Why is the menace response negative in patients with glaucoma?
damage to the optic nerve prevents vision; the menace response requires the animal to have some vision to see the hand and produce the response
What is the normal range for IOP in dogs?
8 to 18 mmHg
What is tonometry?
measurement of intraocular pressure
What are the three methods of tonometry?
-applanation
-indentation
-rebound
Which devices are used for each method of tonometry?
applanation: TonoPen
indentation: Schiotz tonometer
rebound: TonoVet
Why does blepharospasm occur with glaucoma?
elevated IOP is painful; the quicker the increase in pressure, the greater the discomfort
What are some of the more general signs of pain due to elevated IOP?
-lethargy
-anorexia/hyporexia
Why does epiphora occur with glaucoma?
excessive tearing due to the pain from elevated IOP
What are the two types of hyperemia seen in the eye?
-conjunctival injection
-episcleral injection
What are the characteristics of conjunctival injection?
-thin/thread like
-long and twisty
-branching
-move with conjunctival movement
-extend back into conjunctival fornix
-indicates superficial ocular dz
What are the characteristics of episcleral injection?
-shorter and straighter
-thicker/rope like
-do not reach the conjunctival fornix
-indicates intraocular dz like glaucoma or uveitis
What are the characteristics of the normal cornea, in terms of dehydration?
-normal cornea is relatively dehydrated and is 70% water
-relative dehydration is one of the methods that keeps the cornea clear
How is dehydration of the cornea maintained in a normal eye?
-endothelial cells pump aqueous humor that has entered the cornea back into the anterior chamber
-corneal intraepithelial tight junctions tears out of the cornea
What causes corneal edema in glaucoma?
-elevated IOP causes greater hydrostatic pressure, which drives fluid into the corneal stroma
-elevated IOP damages the endothelial cells and decreases their pumping function
What causes mydriasis in glaucoma?
combination of optic nerve damage and ischemic necrosis of the iris sphincter muscle
What is gonioscopy?
visualization of the iridocorneal angle
What is the conventional flow pathway for aqueous humor?
-non-pigmented ciliary body epithelium ->
-posterior chamber ->
-pupil ->
-anterior chamber ->
-pectinate ligament ->
-trabecular meshwork ->
-intrascleral venous plexus ->
-systemic circulation
What is the unconventional flow pathway for aqueous humor?
-non-pigmented ciliary body epithelium ->
-posterior chamber ->
-pupil ->
-anterior chamber ->
-supraciliary space/uveal tissues ->
-systemic circulation
Why is it important to observe the iridocorneal angle?
elevated IOP occurs when there is a problem with aqueous outflow
What is goniodysgenesis?
-malformation of the iridocorneal angle
-pectinates do not form properly and instead are replaced by a solid sheet of tissue
What is rarefaction?
process by which the solid sheet of tissue that forms the iridocorneal angle in utero breaks down to leave pectinate threads with large flow spaces
What is a morphologic diagnosis?
description of the morphological strutcure involved in the disease process and the type of pathology occurring
What is glaucoma?
family of diseases characterized by optic nerve damage and optic nerve degeneration that is associated with elevated IOP
What are the determining factors regarding the permanence of optic nerve damage?
-magnitude of pressure elevation
-duration of pressure elevation
What are the characteristics of optic nerve degeneration?
-once the optic nerve has felt the impact of high pressure, degeneration will continue even if the IOP normalizes
-degeneration progresses more rapidly if IOP is not controlled, so treatment is important despite prognosis
-glaucoma eventually results in blindness
What are the characteristics of primary glaucoma?
-bilateral
-goniodysgenesis causes glaucoma; nothing else needs to occur
What causes secondary glaucoma?
something happens to secondarily clog the iridocorneal angle and cause the pressure to go up
