Amplitude of accommodation and accommodative response

Amplitude of accommodation

dioptric distance between the far point and the near point of accommodation

Far point

point conjugate with the retina of the unaccommodated eye

Near point

point conjugate with the retina of the accommodated

-closest distance that can be seen clearly

Fortmula for amplitude of accommodation

Far point - near point

What is amplitude of accommodation if patient is fully corrected?

its equal to near point

Push up method

advance the target toward the patient until they report the first slight blur

What is first slight blur?

Patiet should still be able to read the letters but they should be slightly blurred

-patient should not be able to clear the letters even if they really try

How can the push up method be measured?

OD, OS, and OU

Why do you need to measure push up method OU?

you need to take convergence into consideration

Does the size of a target matter? Why?

yes

-larger the target gives a higher amplitude due to less sensitivity to changes in blur

-we want to use the smallest target they can see at their near pont

Do we ever really use the smallest target patient can see at their near point?

No because as you move target closer the angle the letters subtend increases

-there are no letters lower than 20/20

Push down method

push target toward patient until they report that it is blurred and then pull the target away from the patient until they say it is clear again

Why do we use push down method?

it can be difficult for patient to know what we mean by slight blur so this will be easier to understand

-there is also a slight pause between when patient sees the change and when they say to stop

What value would be good to determine amplitude of accommodation?

average of the push up and s=push down method

Push away method

start with the target close to the patient and pull it away slowly until they first recognize the target

Why do we use push away method?

mostly for small children

What is issue with push away method?

-end point is not when first blurred it is when the object can first be recognized

-child is being asked to go from zero accommodtion to about 15D which is a difficult jump to make

Minus lens amplitude

keep target at 40 cm, add minus lenses over the patients distance Rx until target first blurs

What is amplitude of accommodation when using minus lens amplitude?

2.50 + amount of minus lens added

Can minus lens amplitude be measured OU?

NO that measures positive relative accommodation (a lower number than amplitude of accommodation

During which test is sensitivity to blur increasing: push up method or minus lens? WHY?

minus lens because adding minus lenses causes minification of the target

Which method involves all of accommodation: push up method or minus lens? WHY?

push up because patient is able to use proximal accommodation because target is being moved

Subjecctive amplitude of accommodation

patient reports the closest distance they can see clearly; based on target position; includes the patients DOF

Objective amplitude of accommodation

doctor measures the position of the point conjugate with the retina; measures what the eye actually does

How can we obtain objective amplitude of accommodation?

1) dynamic retinoscopy

2) dynamic cross cylinder

3) near duochrome

When does patient experience blur when finding amplitude of accommodation?

when distance between stimulus and response exceeds half of the depth of field

Amplitude of accommodation at 10 yo

11D

Amplitude of accommodation at 15 yo

10.25 D

Amplitude of accommodation at 20 yo

9.5 D

Amplitude of accommodation at 25 yo

8.5 D

Amplitude of accommodation at 30 yo

7.5 D

Amplitude of accommodation at 35 yo

6.5

Amplitude of accommodation at 40 yo

5.5

Amplitude of accommodation at 45 yo

3.5

Amplitude of accommodation at 60 yo

1.25

Amplitude of accommodation at 70 yo

1

Hofstetter's equation minimum expected amplitude

15- 0.25(age in years)

Hofstetter's mean expected amplitude

18.5- 0.3(age in years)

Hofstetter's maximum expected amplitude

25- 0.4(age in years)

How did Duane and Hofstetter determine their amplitudes?

based on subjective results

Based on objective measurements of amplitude what was determined?

children have less amplitude that originally thought

Procedure of dynamic cross cylinder

1) correct patient for distance

2) add +/- 0.50 JCC (creates 1D of astigmatism)

3) determine which lines are clearer try to get COLC on retina

Are the horizontal focal lines in front or behind for dynamic cross cylinder?

Infront

-JCC makes patient myopic in the verticle meridian

Will horizontal focal lines always be infront?

yes because you fully corrected the patient for distance making them emmetropic

Which lines will be clearer if patient has a lag of accommodation?

Horizontal focal lines

If patient has a lag of accommodation what lenses do you add?

plus lens (want to bring patients focus closer to them)

If patient has lead of accommodation what lenses do you add?

minus lens

Which lines will be clearer if the patient has a lead of accommodation?

Verticle focal lines

Fused cross cylinder

binocular dynamic corss cylinder

Can monocular dynamic cross cylinder be called fused cross cylinder?

No because you are not fusing an image

What assumptions are made by dynamic cross cylinder?

1) patient does not change their accommodation when veiwing rectilinear target

2) patient does not change their accommodation when lenses are added

What is incorrect about the assumptions made by dynamic cross cylinder?

1) patient will change accommodation to make at least one set of lines clear

2) patient will relax or increase their accommodation inorder to work the least they have to inorder to focus

When is the only time you should use dynamic cross cyliinder or near duochrome to measure a patients lead or lag of accommodation?

Above the age of 35 years old

What is the goal of dynamic cross cylinder and near duorochrome?

to measure lead or lag of accommodation

What is near duorochrome good to use to measure?

if the patient has a lead or lag of accommodation

Is near duorochrome good at measuring how much lead or lag of accommodation a patient has?

No because you have to add lenses inorder to measure lead or lag in this method

Is dynamic cross cylinder a good way to determine whether a patient has a lead or lag of accommodation?

No

What is the only way you should measure amount of lead or lag of accommodation?

Dynamic retinoscopy (specifically cross nott)

Why can you not use methods that require changing lenses to determine amount of lead or lag of accommodation a patient has?

as soon as you add the lenses patients accommodation changes