Intro to IOP and Tonometry Flashcards Preview

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Flashcards in Intro to IOP and Tonometry Deck (27)
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what does tonometry measure

indirect estimation of IOP at one point in time by measuring resistance of eye to deformation by applying force to anterior surface


when should tonometry not be used

1. red eye of infectious origin (exception is herpetic eye disease)
2. severely traumatized cornea
3. open globe
4. hyphema
5. eyes w/ keratoprosthesis (artificial cornea)


what are the structures involved in aqueous humor dynamics

1. limbus
2. main route of aq humor outflow
3. ciliary body (site of aq humor production and other outflow route of unconventional or uveoscleral outflow)
4. iris and lens


what dynamic factors does IOP depend on

1. rate of aq humor production
2. circulation of aq humor
3. outflow of aq humor
4. volume of vit humor
5 elasticity of cornea/scerla (ex. ocular rigidity)


flow of aq humor against resistance generates ____ necessary for shape and optical properties of eye



what is corneal hysteresis

the difference btwn inward and outward applanation pressures
-difference in first/repeated applanation measures
-indication of biomechanical properties of cornea


what is ocular hypotension
what is ocular hypotony
what can you get hypotony from? (2) what are examples

oculular hypotension: IOP below normal range
ocular hypotony: IOP < ~5mmHg
hypotony from aq. loss
-surgery, trauma, RD
hypotony from decreased production of aq:
-infl, medications, proliferative vitreworetinopathy


what is ocular hypertension

IOP above normal range (>21mmHg) w/ no detectable changes in vf or damage to optic nerve


who is at risk for ocular hypertenstion

african americans
age 40+
+family history
high myopia


what is glaucoma

group of ocular diseases w/ various cuases that ultiately are associated w/ a progressive optic neuropathy leading to loss of vision function
-atrophy of the optic nerve and loss of retinal ganglion cells and their axons


what kind or glaucoma patients are usually asymptomatic



what are some signs of glauc

-loss of retinal rim-consequent enlargement of C/D ratio
-elevated IOP
-thin corneas
-thinning/damage of NFL
-drepeatable vf loss
-peripapillary atrophy, flame hem


what are the 2 methods of tonometry

1. indentation
-indentation of cornea
2. applanation
-flattening of cornea


how is IOP determined in goldman applanation tonometry

IOP determined by amount of force needed to flatten a small corneal surface


what is the imbert-fick principle (goldman is based on this)

for dry thin walled sphere, presure inside is equal to the force necessary to flatten the surface divided by the area flattened
-but the cornea is aspheric, wet, and not perfectly flexible, and not infinetely thin soooooo
P+S(surface tension) = F*Ai(inner area cornea) + B (force required to bend cornea)


the 2 beam-splitting prisms w/in the applanating unit optically convert circular area of corneal contact into ____



the prisms of the GAT are adjusted so the ______ of semicicles overlap when 3.06mm of cornea is applanated

inner margins of semicircles


what is the idea thickness of the mires

1/10 diameter of semicircles


what happens if the tonometry mires are too thick
what happens if they are too thin

too thick: IOP will be overestimated-blow some fluid from tips/lids (decrease fluroesine)

too thin: IOP will be underestimated: add more fluorescein


what do you do if the mires are overly pulsating

apply very slightly more pressure, just enough to stop it


if the space w/in (inside) semi-circles are splotchy and indistinct, what is happening

too much pressure is being applied
-pull back slightly on joystick


what irregularly shaped corneas, what would you use to take pressure

use tonopen or NCT
bc irreg shaped corneas will distort mires and have inaccurate measures


if there is high astig how do you do tonometry

if >3D of astig: align markings on tonometer tip to match minus cyl axis of astig


thicker corneas result in _____ IOP
thinner corneas result in ____ IOP
what is the exception

ticker=falsely high IOP
thinner=falsely low IOP

exception: thick corneas due to edema are easier to indent due to high water content and result in falsely low IOP


repeated tonometry measurements push aq out of ant chamber, resulting in what

falsely low IOP
wait 10 sec


tonometry should always be performed ____ other tests that apply force to the eye



artificially high IOP can be a result of...

-pt anxiety
-pressing globe when holding eyelids open
-too tight shirt collar