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

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
which measurement of amplitude is more favorable, objective or subjective
Objective - measuring the point conjugate with the retina where the pt exerts maximum accommodation
26
what are considered objective techniques
dynamic ret autorefraction
27
what are considered subjective techniques
push up push away push down
28
what is always true about the relationship between objective and subjective amplitdue
objective is always < subjective due to blur
29
how do you determine when blur will be reported
when AS - AR > half (DOF in Diopters)
30
Based on Duane's table, what amplitude does a 40 year old have
5.5
31
Hoffstetter Eq: for minimum expected amplitude =
15 - 0.25 * (age in yrs)
32
Hoffstetter Eq: for mean expected amplitude
18.5 - 0.3 * (age in yrs)
33
Hoffstetter Eq: for maximum expected amplitude
25 - 0.4 * (age in yrs)
34
the findings of Duanes are based on what kind of accommodation ?
accommodative stimulus (AS), a subjective amplitude
35
what are the clinical measurements of accommodative response
Dynamic Ret (cross -Nott) dynamic cross cylinder near duochrome
36
What is dynamic cross cylinder
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
if a patient has a LAG of accommodation, which FL is closer to the retina
HFL are closer, thus they appear clearer to them AR < AS
38
In dynamic cross cylinder , plus spheres are added until
the two sets of lines appear equal (COLC on retina)
39
the amount of plus added to achieve equality equals
lag of accommodation
40
if a pt has a LEAD of accomm. which FL will be closer to the retina
VFL are closer to retina, thus appears clearer to pt AR > AS
41
the amount of minuses added to achieve equality equals
the lead of accommodation
42
what happens when a pt accomm. accurately on the target
AS = AR VFL and HFL are equidant from target, both lines appear clear
43
how is dynamic cross cylinder measured
binocular and monocularly
44
what age qualifies for accurate dynamic cross cylinder measurement
35yr old +
45
for near ducochrome test what does pt response of green and red mean respectively ?
green = lag of accom red = lead of accom
46
what is duochrome testing measuring vs. not ?
helps identify the presence of lead and lag but not the measurement of how significant it is