glaucoma Flashcards
Aqueous humor dynamics
aqueous humor produce in ciliary body
passive and active process
active-most important, secretion against concentration gradient
Circulation of aqueous humor
secretion into posterior chamber
enters anterior chamber through pupil
circulates within anterior chamber
exits anterior chamber via iridiocorneal angle
aqueous humor conventional outflow
from ICA into intrascleral venous plexus the into vortex veins
accounts for majority of aqueous humor outflow
aqueous humor unconventional outflow
uveoscleral outflow
through iris root into supraciliary and suprachoroidal space
accounts for less aqueous humor outflow
intraocular pressure
normal 10-25 mmHg
should not vary between eyes by more than 20%
balance between aqueous humor production and outflow
diurnal and seasonal fluctuation
glaucoma definition
IOP>30 mmHg
elevated IOP causes death of reintal ganglion cells and their axons–>visual field loss & blindness
always due to decreased outflow
primary or secondary
acute glaucoma
episcleral venous congestion
corneal edema
mydriasis
blepharospasm
epiphora
optic nerve pallor
blindness
usually a dog
chronic glaucoma
episcleral veous congestion
corneal edema
mydriasis
blepharospasm
epiphora
optic nerve pallor
blindness
buphthalmos
Haab’s stria
deep corneal vascularization
lens (sub)luxation
optic disc cupping
tapetal hyperreflectivity
reintal vascular attenuation
dx of glaucoma
signalment
hx
clinical sxs
tonometry
gonioscopy-primary vs secondary
types of tonometry
indentation-Schiotz
applanation-Tono-penVet
Rebound-TonoVet
Schiotz tonometer
measures force required to indent cornea
topical anesthesia req
positioning is challenging
not recommended for weak corneas
Reasonable estimation of IOP
Applanation Tonometry
measures forse required to flatten cornea
+/- topical anesthesia
can be used on diseased corneas
easier to use than Schiotz
variable readings with inexperience
rebound tonometry
measures return bounce of probe from cornea
can be used on diseased corneas
accurate and reproducible readings
primary glaucoma
genetic dog disease
bilateral
primary open angle glaucoma<<primary angle-closure glaucoma>
<p>
Females>males</p>
</primary>
primary open angle glaucoma
biochemical alterations within trabecular network
greater resistance to aqueous humor outflow
insidious bilateral IOP elevation
Clinical disease not apparent until 2-5 years of age
primary angle closure glaucoma
micromovements causing blockage at pupil
decline of meshwork facility
sudden unilateral IOP elevation
fellow eye follows in 8 months
clinical disease not apparent until 4-10 years of age
most common presentation of primary glaucoma
acute, unilateral, red, cloudy eye with a dilated, non-responsive pupil in a dog
secondary glaucoma
cats & horses
unilateral or bilateral
concurrent ocular disease-Uveitis, ocular neoplasia, lens luxation, intumescent lens, Aqueous humor misdirection syndrome
intumescent lens
swelling of lens due to increased fluid content
forward displacement of lens
narrowing or closure
aqueous humor misdirection syndrome
aka malignant glaucoma
ciliary body-vitreous-lens block
posterior flow of aqueous humor into vitreous cavity
build up of vitreous and aqueous humor pushes lens, iris and ciliary body anteriorly
pupil becomes obstructed
ICA narrows and closes
cats
secondary glauoma presentation
may be acute or chronic
affected eyes may be visual or blind
one or both eyes affected
cats, dogs and horses
goals of medical therapy
reduce and maintain IOP to level that is compatible with ocular heatlh
preservationo of vision
comfort
two main mechanisms for medical therapy
reduce aqueous humor production
increase aqueous humor outflow
main class of drugs used to tx glaucoma
osmotic diuretics
beta blockers
carbonic anhydrase inhibitors
prostaglandin analogues
osmotic diuretics-Mannitol
osmotic gradient pulls fluid from eye-decreases ultrafiltration, shrinks vitreous volume
lowers IOP within 1 hour
emergency management of acute glaucoma
caution: less effective in inflamed eye, avoid in CV dz, deh p, CKD
can cause cerebral deh–>nausea, vomiting and altered consciousness
Beta blockers-Timolol 0.25%, 0.5%
decreases aqueous humor production
BID
use for prophylactic tx of unaffected, fellow eye in primary glaucoma, maintenance therapy (with CAI)
caution: CV dz, bronchial asthma, cats, small dogs
carbonic anhydrase inhibitors-
decrease aqueous humor production
combine with beta blockers
Dorzolamide-topical
systemic-Methazolamide, Acetozolamide
maintenance therapy
caution: cats, diuresis, GI disturbance, Metabolic acidosis, hypokalemia
Prostaglandin analogues
increase uveoscleral outflow and decrease aqueous production
latanoprost, travaprost, bimatoprost, unoprostone
topical SID, BID
rapid reduction in IOP
DOGS ONLY!
maintenance and emergency cases
caution: extreme miosis occurs
surgical therapy goals
reduce and maintain IOP within normal limits
preservation of vision
comfort
still need medical management
surgical therapy indications
glaucomatous eye for which medical management is no longer effective
visual eye
surgical therapy main mechanisms
reduce aqueous humor production
increase aqueous humor outflow
laser cyclophotocoagulation
destruction of ciliary body processes–>decreased aqueous humor production
fair to good for maintenance of IOP
Adverse effects: post-op IOP spike (manage with meds), uveitis, cataract, staphyloma, retinal detachment, ciliary body process regrowth, phthisis bulbi
anterior chamber shunt
silicone tube in AC drains fluid outside of the eye
primary glaucoma in dogs
fair for control of IOP
adverse effects: obstruction, implant migration
when is salvage procedures indicated?
glaucom a that presents chronically
when medical and surgical management fail
enucleation
removal of globe, eyelid margins, conjunctiva and third eyelid
potential complications: very uncommon, wound infection, woud dehiscence, blindness of fellow eye
evisceration and prosthesis
removal of ocular contents, leaving only cornea and sclera
prosthesis put in
complications: KCS, delayed/impaired health of corneal ulcers, dehiscence of surgical site
extrusion of implant
intravitreous gentamicin
Gentamicin is toxic to ciliary body and retina
combined with dexamethasone to decrease inflammation
indicated only if general anesthesia can’t be performed/finances
65% success rate
caution-renal disease, ocular sarcoma
