glaucoma Flashcards
What are the 3 components of trabecular meshwork
uveal (at iris root), corneoscleral (sheets spanning from scleral spur to scleral sulcus), juxtacanalicular (major site of outflow resistance; next to canal of schlem)
What are the 3 mechanisms that aqueous enters the posterior chamber?
active secretion (via Na-K pumps), ultrafiltration (hydrostatic and oncotic pressures), and diffusion (movement of ions down concentrations gradient
aqueous production is via what kind of cells?
non pigmented ciliary cells
what is the Goldmann Equation of IOP?
IOP=(formation of aqueous-pressure insensitive uveoscleral pathway)/(Pressure sensitive trabecular pathway+episcleral venous pressure)
what are the two pathways of aqueous outflow?
via trabecular meshwork (schlem to episcleral veins) and uveoscleral pathway (root of iris/ciliary body to suprachoroidal space)
POAG risk factors
elevated IOP, African American, FMHx, thin corneas, age, decreased perfusion pressure, ischemic vascular diseases (HTN, DM…etc)
PACG risk factors
women, hyperope, inuit/asian
when is peak IOP during the day
early AM; decreases by half during sleep.
What is the rate of aqueous production
2-3microliters/min
what is the venous outflow path from canal of schlem?
schlemm to episcleral veins to anterior ciliary and superior ophthalmic veins then to cavernous sinus
what happens to cross section of canal of schlemm as IOP increases
cross section decreases as trabecular meshwork expands
uveoscleral drainage decreases with age and glaucoma. What increases uveoscleral drainage?
cycloplegics, adrenergic, prostaglandins.
Miotics decreases uveoscleral outflow
what 4 conditions increase episcleral vein pressure?
cavernous-carotid fistula, cavernous thrombosis, sturge weber, thyroid eye disease
what are factors influencing IOP?
time of day
body position, exercise, HR, BP, respiration
Fluid intake
Meds
what principle is tonometry based on?
Imbert Fick Priciniple
What is the inbert fick principle?
The pressure in a dry thin walled sphere equals the force necessary to flatten its surface divided by the area of flattening. P=F/A
What is the area that is flattened on Goldman application
3.06 mm diameter of the cornea
too much fluoresceine on Goldmann applanation leads to what falsely high or low pressures
high
what is CCT
central corneal thickness
whats normal CCT
520 microns
why are tonopens and pneumatic tonometers (both are Mackay Marg Type tonometers) useful for patients with corneal edema or scars?
because it only interacts with a small area of the cornea
what kind of tonometer is good for Peds?
rebound tonometer because it doesn’t require topical anesthesia
How does the Schiotz tonometer work?
It indents the cornea with a known weight to be converted to IOP
what are three ways to clean tonometer prisms?
1:10 bleach, 3% hydrogen peroxide, 70% isopropyl alcohol for 5 mins.