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Binocular vision- my one > 7. Accommodation > Flashcards

7. Accommodation Flashcards

1
Q

What is accommodation?

A

The ability of the lens to change shape to obtain a clear image of a near object

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2
Q

What lenses stimulate and relax accommodation?

A

Minus lenses stimulate accommodation

Plus lenses relax accommodation

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3
Q

How do you assess accommodation?

A

Amplitude of accommodation

Accommodative facility

Accommodative lag or lead

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4
Q

How do you measure amplitude of accommodation (AoA)?

A

Measure Near point using RAF rule

Minus lenses

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5
Q

How can you measure AoA using RAF rule?

A

Px wears full distance rx (max plus and minumum minus)

Use smallest target they can read eg. N5 and bring it closer to them until it blurs then pull back until its clear

Test monocularly and binocularly 3 times

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6
Q

Why does px need to wear full distance rx for measuring accommodation?

A

If px is hyperopic and not wearing their distance rx then they are already accommodating

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7
Q

What unit is AoA recorded in?

A

Measure in cm and covert to dioptres

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8
Q

What do you record for AoA?

A

If difference between the blur and clear is less than 1, record the mean, if greater than 1 record the range

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9
Q

If you are measuring AoA for a presbyope and if you gave them a +2.00 reading add, how do you calculate the final result?

A

Subtract the add from the final near point result

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10
Q

What is the normal value for AoA dependant on?

A

Age- AoA reduces with age

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11
Q

What is the normal value for AoA for px under 10

A

15 dioptres

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12
Q

What is the normal value for AoA for 11-20 yr old?

A

10 dioptres

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13
Q

What is the normal value for AoA for 11-21-30 yr old?

A

6 dioptres

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14
Q

Over 60 AoA?

A

Around 0

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15
Q

How to you record AoA?

A

AoA RAF: Binoc with rx 10D x3

Monoc, RE 8D, LE 8D x3

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16
Q

What is another way of measuring AoA?

A

Minus lenses

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17
Q

How do you use minus lenses to measure AoA?

A

Px wears full refractive correction, one eye occluded, hold near chart at 40cm, keep adding minus lenses in 0.25 steps

Encourage px to make print clear and stop when can no longer be cleared

Repeat with other eye and binocularly

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18
Q

When are minus lenses used as a method to measure AoA

A

In research as it’s too time consuming in practise

19
Q

What is Accommodative facility?

A

The ability to change accommodation with demand i.e how quickly you can stimulate and relax accommodation

20
Q

Give a real life example of change in accommodation

A

In a lecture hall looking at the board then looking at your notes infront of you

21
Q

How do you measure accommodative facility?

A

Flipper lenses

22
Q

How do you use flipper lenses to measure accommodative facility?

A

Give patient near chart , must wear full rx and put on 1 minute timer

Hold plus side flippers infront and say can you tell me when the print becomes clear then flip to minus and say again can you tell me when it’s clear

23
Q

What do you record in accommodative facility?

A

Number of cycles per minute

24
Q

What counts as 1 cycle?

A

The plus and minus 1 flip of each is one cycle

25
Q

What dioptre flipper do you start with and what happens if px can’t do it?

A

Start with +2.00 flippers then reduce strength if px can’t do it

26
Q

What is the normal values for accommodative facility for a normal young adult or child?

A

9/11 cycle per minute with +2.00 flippers

27
Q

What do you record for accommodation facility result?

A

(full rx worn, size of print, cycles per minute, flipper size used

28
Q

Is AoA and accommodative facility objective or subjective ways to assess accommodation?

A

Subjective

29
Q

What are the disadvantages of subjective assessment of accommodation?

A

Unreliable

30
Q

What is an objective way to assess accommodation?

A

Measuring accommodative lag or lead using dynamic ret

31
Q

What is accommodative lag?

A

Under-accomdating

32
Q

What is accommodative lead?

A

accommodating

33
Q

What are the two methods of dynamic ret?

A

MEM

Nott

34
Q

Describe how you would use MEM method to measure lag or lead?

A

Wear full distance rx, target same distance as ret at 40cm (attachment card that comes with retinosocpes)

A with movement indicates lag

An against indicates lead

Neutralise the movement you see

35
Q

How do you know if their accommodation is perfect and accommodating exactly to the demand so no lag or lead?

A

Neutral reflex

36
Q

What does AC/A mean?

A

Amount of accommodative convergence per dioptre of accomdation

37
Q

Describe AC/A in more simpler terms

A

It’s how much your eyes converge when you accommodation by 1 diopters

38
Q

Does AC/A ratio change with age?

A

No, the AC/A ratio we develop when we were young stays until presbyopia

39
Q

What is a normal AC/A ratio?

A

3:1 to 5:1

40
Q

If patient has 12 dioptres of exophoria, what lenses and power do you give so eyes pull in?

A

-3 as minus stimulates accom so eyes will pull in

41
Q

What are the 3 different ways to measure AC/A ratio?

A

Heterophoria method

Gradient method

Fixation disparity method

42
Q

Describe the Heterophoria method

A

Wear distance rx, measure hetrophoria or tropia and distance and near, measure the PD

Use this formula
AC/A= PD in cm+(AngleN- AngleD) /(Accommodative demand)

For eso use a + sign and for exo a minus sign

43
Q

What is the accommodative demand?

A

It depends on where you hold the targer so if it’s head at 1/3m(33cm) then the demand is 3 dioptres

If it’s held at 50cm then the demand in 2 dioptres

Binocular vision- my one (11 decks)

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