Glaucoma Vol. 1 Flashcards
Name the 3 anatomical factors that determine lOP.
- Rate of aqueous humor production 2. Resistance to aqueous outflow 3. Level of episcleral venous pressure
What is preperimetric glaucoma?
Glaucomatous changes of optic disc in patients without visual field defects
What is the the specific site of aqueous outflow resistance generally considered to cause primary open-angle glaucoma?
Juxtacanalicular meshwork
What is the most common cause of non-reversible cause of blindness in blacks?
Glaucoma
Name 3 anatomical characteristics that may make African-Americans more susceptible to glaucoma.
- Larger optic discs 2. More nerve fibers 3. Thinner central corneas
What ethnic group has the highest prevelance of PACG?
Inuit populations of the Artic
What gender is at higher risk for PACG?
Women
How does the anterior chamber change with age?
Anterior chambers decreases in depth and volume with age
What is the most common age associated with acute angle-closure glaucoma?
Age 55 to 65
What type of refractive error is at increased risk of PACG?
Hyperopia (due to decreased anterior chamber depth)
What protein produced by trabecular meshwork cells has bean linked to genetic studies of POAG?
Myocilin (TIGR protein)
What gene was the first to be associated with POAG?
GLC1A
What protein is produced by the GLC1A gene?
TIGR/MYOC
What type of glaucoma has been associated with GLC1B and GLC1E gene?
Low-tension glaucoma
On what chromosome is GLC1A gene found?
Chromosome 11
On what chromosome is GLC1C gene found?
Chromosome 3
What structure creates the aqueous humor?
Ciliary processes
What chromosome has been associated with nanopthalmos associated glaucoma?
Chromosome 11
What specific cells of the ciliary processes are the actual site of aqueous humor production?
Inner, nonpigmented epithelial cells
What type of transport mechanism accounts for the majority of aqeuous humor production?
Active transport
What is the average production rate of aqueous humor?
2.0 to 2.5 uL/min
What is the most common method used to measure rate of aqueous formation?
Fluorophotometry
What gene is associated with aniridia and glaucoma?
PAX-6 gene
What is the average rate of outflow of aqueous humor?
0.2 to 0.3 uL/min/mmHg
How are aqueous humor production and outflow change with age?
Both are decreased
What artery supplies the ciliary processes?
Major arterial circle of the iris
What is the average turnover rate of aqueous humor?
Approx. 1% per minute
Nama the 3 layers of the trabecular meshwork.
- Uveal 2. Corneoscleral 3. Juxtacanalicular
Name 3 classes of glaucoma drugs that cause decreased aqueous formation.
- alpha-2 agonists 2. Beta-blockers 3. Carbonic anhyrdase inhibitors (Think “ABC”)
What is the average diameter of Schlemm’s canal?
370 um
What two veins does Schlemm’s canal drain into?
Anterior ciliary and superior ophthalmic veins
What vessel do the anterior ciliary and superior ophthalmic veins drain into?
Cavernous sinus
What is the average value of episcleral venous pressure?
8 to 10 mmHg
Name 2 systemic diseases associated with increased episcleral venous pressure.
- Facial hemangioma (age. Sturga-Wabar) 2. Thyroid-associated orbitopathy
How does alcohol consumtption affect lOP?
EtOH causes transient decrease in lOP
How does acidosis affect lOP?
Metabolic or respiratory acidosis causes decreased lOP (decreases aqueous humor production}
How does pregnancy affect lOP?
Pregnancy generally causes decreased lOP
How does heroin and marijuana affect lOP?
Heroin and marijuana cause decreased lOP
On average, how much does lOP fluctuate of an individual within a 24-hour period?
2 to 6 mmHg
During what time of the day does peak IOP tend to occur in the average person?
In the early morning hours
What is the size of area of the cornea flattened by Goldmann applanation tonometry?
3.06 mm (Think Fick principle)
How is lOP affected by body position?
lOP is higher in recumbent pressure (due to increased episcleral pressure)
What does an elliptical fluorescein pattern during Goldmann tonometry typically indicate?
Corneal astigmatism
What are the two ways lOP can be measured with an elliptical fluorescein pattern?
- Red mark set at the least curved meridian of the cornea 2. Two averaged pressure readings taken 90
How is lOP affected by body temperature?
Elevated body temperature causes increased lOP (due to increased aqueous humor production)
How is lOP affected by hypothyroidism?
Hypothyroidism causes increased lOP
How does aerobic exercise affect lOP?
Aerobic exercise causes decreased lOP
How do soft contact lenses affect lOP measurement?
Soft contact lens causes falsely low lOP measurement
At what corneal thickness is Goldmann tonometry most accurate?
520 um
How does central corneal thickness affect lOP measurement?
Increased CCT causes falsely high lOP measurement (and vice versa)
How do depolarizing muscle relaxants, such as succinylcholine affect lOP?
Depolarizing agents cause decreased lOP
What is the population mean CCT?
542 um
How does the amount of fluorescein affect lOP readings?
Too much fluorescein causes falsely elevated lOP (and vice versa)
How does corneal edema affect lOP measurement?
Corneal edema causes falsely low lOP measurement
Is IOP typically under or overestimated with air-puff tonometer?
Air-puff tonometer typically overestimates lOP
How does corneal scarring affect lOP measurments?
Corneal scarring causes falsely high lOP measurement
How does scleral buckle procedures affect lOP measurment?
Post-surgery lOP measurement after scleral buckle may cause falsely low measurement
By how much does lOP measurement differ from actual lOP for each 10 urn difference in CCT?
Measurement differs from actual lOP by 0.5 mmHg with each 10 urn change in CCT from the average
According to the OHTS, how does CCT affect an individual’s risk of developing POAG?
Individuals with CCT of 555 um or less have three-fold greater risk of devoloping POAG
When is the use of Tono-Pen particularly useful?
In individuals with corneal scars or edema
