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OT > Amplitude of Accommodation > Flashcards

Amplitude of Accommodation Flashcards

1
Q

What is amplitude of accommodation

A

the dioptric distance between far point and near point of accommodation

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2
Q

What is far point

A

point conjugate with the retina of the unaccommodated eye

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3
Q

what is the near point

A

point conj. with retina of max accomm eye (for objective amplitude) OR closest distance that can be seen cearly (for subjective amplitude)

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4
Q

The equation for amplitude says

A

AMPL = FAR PT (D) - NEAR PT(D)

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5
Q

If an uncorrected 3D myope has a near point of 25cm, what is the amplitude

A

AMP = -3 - (-4)
AMP = 1D

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6
Q

What are the 5 methods to measure amplitude of accomm

A
  1. push up
  2. push down
  3. push away
  4. minus lens (ML)
  5. objective techniques (dynamic ret and autorefractor)
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7
Q

What is push up

A

a target is pushed towards the pt until they report first sigh of sustained blur (FSSB)
- this represent pt near point
- when pt is corrected near pt = amplitude

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8
Q

how can the push up technique be measured

A

OD, OS and binocular OU

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9
Q

How is target size relevant

A

change in target size = change in ability to notice blur
- lowering target size = increased blur detection = decreased amplitude .. occurs in PUSH UP
- increasing target size = decrease blur detection = increased amplitude .. occurs in MINUS LENS

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10
Q

according to snellens fraction m the patients near point can also be

A

the viewing distance, numerator of fraction

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11
Q

What is the push down technique

A

similar to push up, the target it brought towards the pt until full blur > push away until fully clear

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12
Q

typically the responses of push up are

A

over estimate of the actual amplitude

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13
Q

typical responses of push down are

A

under estimate of the actual amplitude

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14
Q

What is push away amplitude

A

placing target close to pt eye, ensure blur > push target away from eye until they can identify the target (not fully clear)

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15
Q

Whats the 2 major problems with push away amplitude

A
  1. end point is when the subject can notice the target, which is not first point of blur > most likely target is farther than needed
  2. children have high amplitudes, hard to make large jumps
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16
Q

What is minus lens amplitude

A
  • target is at 40cm (2.5D)
  • minus lenses added over distance Rx until response for FSSB
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17
Q

What does the amplitude equation say

A

amplitude = 2.50 + added ML before blur
where 2.5D is the AS

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18
Q

each diopter of minus lens power increases the accommodative stimulus by

A

1.00D

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19
Q

How can the minus lens amplitude be measured

A

monocularly only

20
Q

what is proximal accommodation

A

assists to find max accommodation, proximal accommodation should be increased

21
Q

what happens to proximal accommodation during minus lens amplitude

A

stays constant

22
Q

what happens to proximal accommodation during push up

A

increases

23
Q

What is positive relative accommodation (PRA)

A

An increase in accommodation while the vergence remains constant

24
Q

How is PRA measured?

A

adding minus lenses binocularly

25
Q

which measurement of amplitude is more favorable, objective or subjective

A

Objective - measuring the point conjugate with the retina where the pt exerts maximum accommodation

26
Q

what are considered objective techniques

A

dynamic ret
autorefraction

27
Q

what are considered subjective techniques

A

push up
push away
push down

28
Q

what is always true about the relationship between objective and subjective amplitdue

A

objective is always < subjective due to blur

29
Q

how do you determine when blur will be reported

A

when AS - AR > half (DOF in Diopters)

30
Q

Based on Duane’s table, what amplitude does a 40 year old have

A

5.5

31
Q

Hoffstetter Eq: for minimum expected amplitude =

A

15 - 0.25 * (age in yrs)

32
Q

Hoffstetter Eq: for mean expected amplitude

A

18.5 - 0.3 * (age in yrs)

33
Q

Hoffstetter Eq: for maximum expected amplitude

A

25 - 0.4 * (age in yrs)

34
Q

the findings of Duanes are based on what kind of accommodation ?

A

accommodative stimulus (AS), a subjective amplitude

35
Q

what are the clinical measurements of accommodative response

A

Dynamic Ret (cross -Nott)
dynamic cross cylinder
near duochrome

36
Q

What is dynamic cross cylinder

A

a subjective test to quantify the lead or lag of accommodation
- corrects the pt for distance
introducing a +/- 0.50 JCC, negative axis vertical over their distance rx

37
Q

if a patient has a LAG of accommodation, which FL is closer to the retina

A

HFL are closer, thus they appear clearer to them
AR < AS

38
Q

In dynamic cross cylinder , plus spheres are added until

A

the two sets of lines appear equal (COLC on retina)

39
Q

the amount of plus added to achieve equality equals

A

lag of accommodation

40
Q

if a pt has a LEAD of accomm. which FL will be closer to the retina

A

VFL are closer to retina, thus appears clearer to pt
AR > AS

41
Q

the amount of minuses added to achieve equality equals

A

the lead of accommodation

42
Q

what happens when a pt accomm. accurately on the target

A

AS = AR
VFL and HFL are equidant from target, both lines appear clear

43
Q

how is dynamic cross cylinder measured

A

binocular and monocularly

44
Q

what age qualifies for accurate dynamic cross cylinder measurement

A

35yr old +

45
Q

for near ducochrome test what does pt response of green and red mean respectively ?

A

green = lag of accom
red = lead of accom

46
Q

what is duochrome testing measuring vs. not ?

A

helps identify the presence of lead and lag but not the measurement of how significant it is

OT (9 decks)

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