Glaucoma Flashcards
What injury is common to ALL glaucomas?
Death of retinal ganglion cells and their axons
The low and normotensive glaucomas in people are theorized to be due to what?
- IOP spikes
2. secondary circulatory or excitotoxic effects on retina or optic nerve
What is the general trend of incidence of canine glaucoma?
Increasing
What are the 10 most common breeds with glaucoma?
ACS (5.52%) [American Cocker] Basset Hound (5.44%) Chow Chow (4.70%) Shar Pei (4.40%) Boston Terrier (2.88%) Wire Fox Terrier (2.28%) Norwegian Elkhound (1.98%) Siberian Husky (1.88%) Cairn Terrier (1.82%) Miniature Poodle (1.68%)
Some dog breeds have a sex predilection for glaucoma. What sex is more commonly affected?
Females
What was the most common cause of secondary glaucoma?
Lens induced uveitis
What percentage of secondary glaucomas are due to LIU?
81%
Other than LIU, what are the next most common causes of secondary glaucoma?
lens luxation (12.0%) postcataract surgery (5.1%) uveitis of unknown cause (7.1%) hyphema of unknown cause (7.3%) intraocular neoplasms (3.5%)
What is the combined (primary and secondary) prevalence of glaucoma in the dog worldwide?
1.7%
3 possible causes of glaucoma?
- primary
- secondary
- congenital
What are the categories of filtration angle appearance? (2 big categories with 3 subcategories each)
- Open angle
- Closed angle
- Narrow angle
AND - Open ciliary cleft
- Closed ciliary cleft
- Collapsed ciliary cleft
What is the width of the iridocorneal angle measured?
opening of the most anterior portion of the ciliary cleft
In the dog, where is the majority of the angle located?
In the ciliary cleft
What are the 2 categories of primary glaucoma?
Open/normal angle/cleft (acute or chronic)
Narrow/closed angle/cleft (acute or chronic)
What are the 2 causes of congenital glaucoma?
- Pectinate ligament dysplasia
2. Goniodysgenesis
What age group do you usually first see congenital glaucoma?
< 6 months
What is the prevalence of congenital glaucoma?
RARE
What age group do you usually see breed-specific glaucoma develop?
6-10 years
What IOP is usually needed for endothelial dysfunction?
> 40 mmHg
What tends to give lower values at normal values: TonoVet or TonoPen?
TonoVet (yes, really)
What is thought to be more accurate tonometer at high IOPs?
TonoVet
When is IOP highest in dog? Lowest?
Highest in early AM, lowest in late evening
What is the IOP variation from early morning to late evening in: normal dogs? Those with POAG?
Normal: 2-4 mmHg
POAG: 6-10 mmHg+
Describe how blindness occurs secondary to elevated IOP.
Initial event prevents normal AH outflow –> physical changes involving AH outflow obstruction –> elevated IOP too high for normal AXOPLASMIC FLOW and BLOOD FLOW –> RGC dysfunction with ON degeneration and atrophy –> visual field loss/blondness
What type of disease are the canine glaucomas classified as?
a NEURODEGENERATIVE disease
What genetic mutation is seen in Beagles with POAG?
ADAMTS10
What is the ADAMTS10 mutation thought to do?
Alter fribrillin
What is thought to cause optic neuropathy (proposed mechanism)?
Collagen defect = altered pressure resistance
How does lens subluxation seem to contribute to glaucoma?
Loss of zonular tension = iridocorneal angle closure and ciliary cleft collapse
Buphthalmos: what species does it not occur in (and when)?
ADULT human
Haab’s stria (break in Descemet’s) only occurs if what happens to the cornea?
It gets stretched (either chronic glaucoma or acute spike)
How might you end up with pigmentary keratitis secondary to glaucoma?
Buphthalmos –> lagophthalmos with decr blink reflex and incr tear evaporation –> exposure keratitis –> pigmentary keratitis
What secondary abnormality can be seen with the sclera secondary to glaucoma?
Staphylomas
Where are scleral staphylomas most likely to occur in a buphthalmic globe?
where nerves and vessels penetrate (equator)
What cell is present in the trabecular meshwork to clean it up?
Macrophage
How much do pectinate ligaments contribute to resistance of AH outflow?
Almost none unless dysplastic
After the pectinate ligaments, what 3 trabecular meshworks does AH go through?
uveal –> corneoscleral –> juxtacanalicular
What are the 2 outflow pathways?
1) Conventional
2) Uveoscleral
Which outflow pathway is pressure INDEPENDENT?
uveoscleral
What part of the trabecular meshwork causes the highest resistance?
Extracellular matrix
What is the importance of MMPs in glaucoma?
Increase ECM turnover, reduce resistance to AH outflow through meshwork, and lower IOP
What are 3 reasons the iris dilates with glaucoma?
1) lack of sensory input from RGCs
2) impaired neuronal and vascular supply to central iris
3) possibly mechanical opening of iris
What happens to the iris (histologically) with glaucoma, and why is this bad?
Stroma thins and sphincter mm atrophies = pigment dispersion –> can further clog the outflow
When the ciliary body gets so atrophied from glaucoma that IOP os <5 mmHg, what happens to the other structures in the eye?
Cataract, profound corneal edema, retinal detachments, intraocular hemorrhage
Why are canine choroidal vessels especially affects by elevated IOP?
Pressure = decr blood flow thru these vessels, and they poorly autoregulate with decreased blood flow
What IOP is needed to start affecting the choroidal vessels?
> 60 mmHg
What is seen clinically if high IOPs cause choroidal vessel dysfunction?
Chorioretinal degeneration, in a pattern radiating from ONH
What genetic defect is associated with primary lens laxations?
ADAMTS17
How can PLL be differentiated from a secondary lens luxation? (just based on age)?
PLL: young = 1-4 yrs old! (not 6-10 like SLL)
What part of the retina is most susceptible to damage, even from small increases in pressure?
INNER retina = RGCs and NFL; also ONH
What pressure can affect axoplasmic flow?
25 mmHg!!
Elevated glutamate found in animals with glaucoma supports what theory of RGC damage?
Ischemic
Secondary glaucoma from lens luxation issue in what 7 breeds?
FTS CJ BW
Fox terrier, Tibetan terrier, Sealyham terrier
Cairn terrier, Jack Russel terrier
Border collie, Welsh Corgi
What 2 breeds get POAG?
Beagle, Norwegian
What breed has the highest prevalence of glaucoma?
American Cocker Spaniel
What is special about ACS development of glaucoma in the contralateral eye?
Usually happens within a few months
What is special about the disease in the Basset hound? How does this impact treatment?
Like to get concurrent anterior uveitis
Complicates medical and surgical treatment
What breeds often retain vision into late into the disease? (4 breeds)
Chow Chow
Shar Pei
Samoyed
Norwegian Elkhound
How old are most Great Danes that get glaucoma?
Avg 4 yrs
What breed has a dominant mode of inheritance?
Welsh Springer Spaniel
What is the most common cause of secondary glaucoma?
Cataract (another study said anterior uveitis)
What percentage of cataracts dogs will develop glaucoma?
20%
Order from most to least likely to cause glaucoma: anterior luxation, posterior luxation, subluxation
Anterior (73%), subluxation (43%), posterior (38%)
Why is ICLE not jumped to with lens luxation?
High complication rate: glaucoma and RD
3 ways intumescent lens can cause glaucoma
1) pupillary block
2) pushes iris forward = closes angle
2) synechiae from LIU
What are the 2 most common causes of glaucoma in aphakic eyes?
1) Posterior synechiae and PIFMs
2) Anterior synechiae and PIFMs
What clinical changes would make you suspect glaucoma secondary to cataract surgery?
IRIS BOMBE with SMALL PUPIL
When is tPA useful (time range) for fibrin occlusion of pupil?
2 weeks duration
If there is pupillary block in an aphakic eye, what can be done?
1) MEDICAL therapy: scopolamine with phenylephrine, anti-inflammatories (steroids and NSAIDs), systemic CAIs, mannitol
2) SURGICAL therapy: open with blade, hypodermic needle, laser iridotomy, iridectomy, iridencleisis
Why is laser iridotomy usually not appropriate for pupillary block?
Closes in a few days
What time point is the average onset of POH?
~5 hours
Ocular melanosis is seen in what 3 breeds? Which of those 3 is it autosomal dominant?
Cairn terrier (auto dominant)
Boxer
Lab
How does ocular melanosis lead to glaucoma?
uveal melanocytes and melanophages end up in the filtration angle
Where is the clinical presentation of ocular melanosis?
First pigmentation/thickening of iris, then episcleral/scleral plaques, release of pigment into anterior chamber/AH, then deposition into outflow pathways (esp VENTRALLY), slow progression to pigmentation of tapetal fundus
What is the rate of progression of ocular melanosis (to glaucoma)? What is the prognosis?
Rate of progression = SLOW
Prognosis = poor – will obstruct valves
What 2 breeds get pigmentary/cystic glaucoma?
Golden retriever
Great Dane
How old are most goldens that develop GRPG?
~8 yrs
What are the first signs of GRPG?
1) pigment on anterior lens capsule
2) uveal cysts
3) iridal hyperpigementation
4) web-like strange of opaque material in the anterior chamber
5) cataracts
Time from diagnosis of GRPG and glaucoma formation?
5 months (unlike Cairn terrier, where it is slow!)
Prognosis of GRPG?
POOR (all will develop glaucoma and usually end up taking eye out)
What are the 3 most common intraocular tumors of dogs?
1) melanoma
2) adenoma of iris/CB
3) adenocarcinoma of iris/CB
Where do you usually see METASTATIC neoplasia in the eye (what structure)?
Ciliary body (makes sense…)
What 2 neoplasms are the most common metastatic neoplasms of the eye?
1) LSA
2) Adenocarcinomas
What is different in puppies with congenital glaucoma in regards to affect of buphthalmia? (2 things different than the buphthalmic adult)
1) globe may return to normal size if pressure controlled early enough
2) helps protect the ONH and retina, to some degree
What is the post-op IOP for eyes with VALVED and UNVALVED gonioimplants?
Valved: 10-12 mmHg
Unvalued: <5 mmHg
When will unvalved implants develop IOPs equal to that of valved implants? What does this coincide with?
3-6 wks post-op
Fibrosis around the implant
Why are very low IOPs from unvalved implants bad?
Increase excessive fibrin formation, potentially hemorrhage and RD
For endolaser to work in a glaucomatous eye, how much should be endolasered?
180 to ideally 270 degrees
What is the average size of an intrascleral prosthesis?
20-22 cm
How long should a temporary tarrsorhaphy be placed after intrascleral prosthesis? Why?
10-14 days
They usually don’t blink well