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Glaucoma > Lec.3: IOP measurement > Flashcards

Lec.3: IOP measurement Flashcards

1
Q

why does IOP increase with age?

A

outflow facility decreases over time

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2
Q

is true that IOP for females over 40 decreases?

A

false. it increases after 40

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3
Q

what type of excercises are known to double IOP?

A

inversion excercises

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4
Q

how do alcohol, heroin and marijuana affect IOP?

A

decrease IOP

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5
Q

how is IOP affected with caffeine, tobacco and drinking 2 16 oz water bottles in 15 min?

A

increases IOP

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6
Q

in glaucoma what is the most important risk factor that is also alterable?

A

IOP

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7
Q

what type of tonometry is Schiotz?

A

indentation

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8
Q

what are the types of applanation tonometry?

A

goldman, perkins, mackay-marg-tonopen, pneumotonometer and non-contact

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9
Q

in what tonometry method does scleral rigidity play big role?

A

Schiotz. (myopes with weaker sclera give false values)

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10
Q

what is the equation for the modified imbert-fick law?

A

W+S=PxA+B
S=surface tension
B=force required to bend the cornea

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11
Q

what is the average central corneal thickness?

A

520 microns

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12
Q

how would a thicker than average cornea affect IOP measurement?

A

lead to over-estimate of IOP

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13
Q

how would corneal curvature affect the outcome of the IOP measurement?

A

the steeper the cornea the more force required to flatten it

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14
Q

on average do older people have thicker or thinner corneas?

A

thinner (with age thickness decreases)

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15
Q

what biomechanical properties contribute to the corneal structure?

A

rigidity, hydration and elasticity

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16
Q

what characteristic do visco-elastic materials demonstrate?

A

hysteresis

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17
Q

what kind of parameters can be measured?

A

geometric parameters

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18
Q

what kind of parameters cannot be measured?

A

material parameters

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19
Q

if patient has a contagion, what is the best way to clean the tono tip?

A

autoclave

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20
Q

what type of cornea would lead to low pressure reading?

A

thin cornea

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21
Q

what type of IOP estimation would an edematous cornea yield?

A

underestimation of IOP

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22
Q

in refractive surgery how many mircons of cornea are removed to compensate for 1 D?

A

12 microns

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23
Q

what type of trend do we see in IOP if patients have thicker cornea?

A

negative trened with IOP being lower

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24
Q

what does a negative residual slope after correction indicate?

A

over correction (problem)

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25
Q

what are the names of the statistical models that show a negative residual effect?

A

Orssengo and Pye model

Ehlers Model

26
Q

can formulas correct for the error in a population?

A

yes

27
Q

can formulas correct for errors in an individual?

A

no

28
Q

what type of tonometer matches the contour of the cornea so the cornea no longer is a source of error in the measurement?

A

dynamic contour tonometer (PASCAL)

29
Q

how many times per second does the dynamic contour tonometer measure the IOP waveform?

A

100 times/sec

30
Q

what is the radius of curvature of tip of the dynamic contour tonometer?

A

10.5 mm (sufficient for any cornea that is physiologically normal)

31
Q

what is the difference of capillary forces in DCT compared to GAT?

A

forces much greater in DCT

32
Q

according to quality index, which values are acceptable for DCT?

A

1-3

33
Q

according to quality index, which values are unacceptable for DCT?

A

4-5

34
Q

what is the characteristic that results from the difference of inward and outward pressure values?

A

corneal hysteresis

35
Q

what type of property does hysteresis describe?

A

the bending of the cornea

36
Q

what type of hysteresis is less capable of absorbing (damping) the energy of the air pulse?

A

low corneal hysteresis

37
Q

what type of diseases tend to show lower corneal hysteresis?

A

keratoconus, fuchs and glaucoma (on average)

38
Q

what tonometry method is not significantly affected by corneal thickness? and which is not?

A

DCT not significantly affected

GAT significantly affected

39
Q

how are DCT and GAT affected by corneal curvature?

A

they are not significantly affected

40
Q

why is DCT more repeatable than GAT?

A

DCT has a lower intra/inter observer variability than GAT does

41
Q

how can fluid pockets acquired from post refractive surgery affect IOP measurement?

A

cause a gross underestimation

42
Q

what type of medication is prescribed after refractive surgery and has the ability to elevate IOP?

A

steroids

43
Q

was there a significant decrease in IOP after refractive surgery when measured by DCT?

A

no, however GAT readings decreased (underestimation)

44
Q

what is the relationship between IOP error and Goldman tonometry?

A

not linear

45
Q

how is blood flow affected in patients with normal tension glaucoma?

A

lower amount of blood getting to the eye

46
Q

what is the chance that patient has normal tension glaucoma if they have an ocular pulse amplitude (OPA) of less then 2 mmHg?

A

80% chance of NTG

47
Q

what does OPA (ocular pulse amplitude) refer too?

A

overall pressure of the eye?

48
Q

how are IOP and OPA related?

A

inversely related

49
Q

is OPA influenced by both IOP and corneal thickness?

A

no just IOP

50
Q

can you diagnose glaucoma based on hysteresis and corneal thickness alone?

A

no

51
Q

is corneal hysteresis correlated with lamina cribrosa hysteresis?

A

yes

52
Q

what tonopen setup mistake will result in a flawed IOP reading?

A

if the cap is on too tight (plunger wont have enough space to move)

53
Q

are tonopen readings reliable?

A

no (below the standard of care)

54
Q

how long after removing contact lenses should an IOP reading be taken?

A

2 hours

55
Q

what type of tonometer does not come into contact with the cornea?

A

diaton tonometer

56
Q

what are the advantages of permanent IOP devices?

A

not influenced by ocular parameters, direct anterior chamber measurements

57
Q

what are the disadvantages of permanent devices?

A

invasive, sub conjunctival devices may not be as accurate

58
Q

what are the advantages of temporary devices?

A

non invasive, not permanent

59
Q

what are the disadvantages of temporary devices?

A

eye movement may have greater effect when compared to permanent devices, surface tension, light exposure, temperature, change in sleeping posture

60
Q

for CL IOP measuring devices, what is the repeatability percentage?

A

35%

61
Q

is it true that PASCAL and ORA are more accurate than GAT?

A

yes

62
Q

when may you want to use a tonopen?

A

when measuring IOP on scarred or damaged cornea

Glaucoma (12 decks)

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