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OV2018 binocular vision > Accommodation and convergence > Flashcards

Accommodation and convergence Flashcards

1
Q

What is the definition of convergence ?

A

simultaneous rotation of the eye inwards

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2
Q

What are the 2 methods you can use ti measure near point of convergence ?

A

Pen to nose
An inaccurate technique
Provides an estimate of the n.p.c.

RAF rule
Dot provides a fixation point
Single high contrast line helps recognition of diplopia
Use cm scale for measurement

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3
Q

What method do we use in the UK to measure near point of convergence ?

A

RAF rule

  • line with a dot in it, bring it closer and closer to the px and ask when that line turns into 2 - get diplopia
  • then will read off the cm scale
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4
Q

Will the px be asked to wear their correction or not ?

A
  • rule of thumb is : if they are a high hyperopia, presbyope , moderate to high myopes should all wear glasses.
  • If px required to wear spectacles to see clear at near then ask them to put them on.
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5
Q

How do you measure using RAF rule ?

A

line with dot

  • hold RAF rule in a slightly depressed angle.
  • then going to bring the target closer and closer till they can see double
  • you will move it very slowly at about 1-2cm per second and record where double occurs
  • once double occurs then you can pull it back and ask when it turns into single
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6
Q

What would you do if px may have convergence and fatigue?

A

would repeat the RAF rule 3 times as the first time could be normal but then 2nd and 3rd may be reduced

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7
Q

What is normal near point convergence ?

A

-if you are pre-presbyopic - expect to get a normal near value of 10cm or less

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8
Q

what can you get your convergence down to if you are a pre-presbyope ?

A

-get down to 5cm before your convergence breaks and recovery is at 7cm
(happens when using the budgie stick or pen torch and not the Raf rule - anything 10cm or below is normal)

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9
Q

What is normal near point value for presbyope px ?

A

15cm

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10
Q

What are the 2 ways to test convergence ?

A

objectively

subjectively

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11
Q

Why do we test objectively the most ?

A
  • for children
  • because if you ask a child to tell when it goes double - they will think that’s the correct answer and will tell you double
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12
Q

How do we test subjectively ?

A

-ask the px when the line goes double- reports diplopia

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13
Q

How do we test objectively ?

A

-watch where the point where one eye or both eyes diverges and then note the distance where that occurs and ask when they may be able to report diplopia

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14
Q

How do you write down the results for when testing objectively ?

A

e.g

RAF conv with Rx : binocular 10/15/20cms RE diverged with diplopia

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15
Q

What is the definition of accommodation ?

A

Is the ability to change the convexity of the crystalline lens in order to obtain a clear image of a near object

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16
Q

What are the 3 assessments of accommodation ?

A
  1. Accommodative amplitude or range
    - Near point- with RAF rule
    - use Minus lenses also
  2. Accommodative facility
    - measure using Flipper lenses
  3. Accommodative lag or lead
    - using Dynamic retinoscopy
    1. Monocular Estimation Method
    2. Nott Method
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17
Q

How do you measure the near amplitude or range ?

A

-using RAF rule
- the target for reading- ask px to read the smallest sentence they can read - e.g N5 so they would use that as target
-Test monocularly and binocularly
-Ensure FULL distance Rx is worn
Maximum +ve or least -ve

  • Find nearest point of clear vision
  • measure in cm and convert to dioptres
  • use dioptric scale
  • bring it closer and closer to the px and ask the px tor report when the lines get blurred.

-Target
N5 or smallest visible print or target

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18
Q

What do we have to ensure when doing any accommodation test ?

A
  • make sure the px is wearing the full distance rx
  • this is because if px was hyperbole and wasn’t wearing correction - they would accommodate to see so would have to make sure they are fully corrected before testing for accommodation.
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19
Q

What is the technique for measuring near point amplitude using RAF rule ?

A

-push up target until patient reports target blur
-Pull back until patient reports target as clear
-repeat push up / pull back
if difference < 1D record mean
if difference > 1 D record range

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20
Q

What happens to px amplitude when presbyopic ?

A

low amplitude of accommodation

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21
Q

What do we recommend in presbyopic px with less than 2D ?

A
  • as their accommodation is low - include a binocular near addition of +2.00 infront of both eyes and subtract this at the very end from their final near amplitude
  • if you were to get 5D then you would subtract 2D = 3Dioptres
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22
Q

What does amplitude of accommodation vary with ?

A

age

  • the older you get the lower it gets
  • the normal values are on the RAF rule table for specific ages
23
Q

How to write down the amplitude of accommodation results ?

A

-first what test you are doing

E.G RAF or AoA Binocular with Rx: 10 D x3 or Monoc with Rx RE:8D x 3 and LE 8D x 3

24
Q

How can you measure near amplitude of accommodation using minus lenses ?

A
  • Full refractive correction
  • hold Target near card at 40cm
  • One eye occluded
  • slowly put Negative lenses are placed in front of eye
  • Increased in 0.25Ds steps
  • can take px 10sec to accommodate in to these lenses hence would take long
  • Encourage patient to make the print clear
  • End point when letters can not be cleared and the print is blurred
  • Repeat for other eye and binocularly
25
Q

What is accommodative facility ?

A

Change in accomodative effort with change in accommodative demand

e. g if px look in distance they need to relax accommodation then the px looks at near then need to accomodate
- so its speed of change in different accommodative states that we are assessing with this test
- rapid refutation from near to distance viewing

26
Q

How do we test for accomdaitve facility ?

A

-MAKE SURE THEY ARE WEARING THEIR FULL DSISTANCE CORRECTION
using flipper lenses-
-one side of the lens is plus and the other is minus
-common one to use + and - 2 D flipper
-ask px to. look at smallest size print
-record the size of print
-then put up flipper lenses and ask when the print becomes clear as soon as the print is clear
-then flip towards the other side of lens and keep flipping until the px sees clear again
-record per min of clear plus and minus

27
Q

What is the normal results cycle for accomdative facility for a young adult or child ?

A

approx 10 cycles of both + and - 2D per minute

28
Q

What do we record for accomdative facility flipper test ?

A
  • Whether wearing Rx
  • Strength +/- flippers
  • No. of cycles /minute
  • Size of print
29
Q

What are some disadvantages of these subjective assessment for accommodation ?

A

-An unreliable endpoint
Particularly children
-Large difference between stimulus and response accommodation
-depth of field
-small pupils, increased depth of field
-Changing subjective criteria

30
Q

What are the objective techniques based by ?

A

their :
Accommodative lag

  1. Stimulus accommodation
    Distance of fixation target in D Sphere
  2. Response accommodation
    Objective assessment of accommodation- is there a lag ?
31
Q

What is the technique used for objective techniques ?

A

Dynamic retinoscopy

32
Q

What are the 2 methods of dynamic retinoscopy ?

A

Nott method

MEM- monocular estimation method

33
Q

How to do MEM in measuring accommodation ?

A

-wear distance rx
hold retinoscope at 40cm
-clip on a card with either pictures or words/letters
-ask px to look at target
-carry out retinoscope -use medium light situations
-say to px to look at picture and carry out retinoscope
- see whether they have an accomodative lag or lead.
-do only 2 swipes as the px can start to relax into the lenses - and then take away the lenses

34
Q

What happens if px accommodates perfectly in the MEM test ?

A

in retinoscope you will see a neutral / reversal reflex

35
Q

What happens if px does not accommodate sufficiently in the MEM test ?

A

the rays of light will fall behind the eye and will Get a with movement (accomdative lag)
-then neutralise this with + lenses

36
Q

What happens if px over accommodates in the MEM test?

A

rays of light fall infront of retina giving against movement (accomdative lead)
-neutralise with negative lenses

37
Q

How to do the nott method in dynamic retinoscopy ?

A
  • you have a ruler with a stimulus on a picture with a px looking at
  • put stimulus at 1/3m to begin with
  • put ret at the same distance
38
Q

What happens if px accommodates perfectly in Nott method ?

A

will see a neutral movement

39
Q

What happens if px has an accomodative lag in the Nott method ?

A

will see a with movement

  • not accommodating sufficiently
  • will need to pull your retinoscope further backwards until you see a neutral movement and will record along the ruler at what distance that occurred ..
  • keep stimulus at same distance
40
Q

What happens if px has an accomodative lead in the Nott method ?

A
  • will see an against movement
  • over accomodating
  • need pull the ret further forward the ruler until you get neutral movement and record-keep stimulus at same distance
41
Q

an EXAMPLE of nott method?

A

target held at 1/3m

  • the accommodative demand is 3D- we want the px to accommodate at this but unfortunately they could not
  • they had a lag with movement
  • and pulled ret further backwards- at 40cm found neutral movement
  • so 1/40= 0.025 - 2.5 D the px could accommodate at
  • therefore in this px the px had a lag of 0.50 D
42
Q

What is a normal lag result ?

A

between 0-0.75 Dioptres

43
Q

What is definition of AC/A. ratio ?

A

Amount of accommodative convergence per dioptre of accommodation (Δ / DS)

44
Q

What is an example of AC/A ratio measured on px ?

A

e. g px measured and has a AC/A to ratio of 4:1 - means every time the px accommodate by 1D the eye pulls in by 4
- also had carried out cover test- had exotropia- at 12 D
- what can we give px to control exotropia and how much minus lenses should give to control their exotropia?

45
Q

-what can we give px to control exotropia ?

A

-try to pull in eyes- give minus lenses- which stimulates accommodation and therefore convergence and help to move eyes in

46
Q

how much minus lenses should give to control their exotropia in the example ?

A

4:1 ratio

so give -3.00 D lens - as will control 12 D

47
Q

What does it mean the higher the AC/A ratio ?

A

the less lenses you need to give them in order to help control their deviation

48
Q

What do we need to know about +ve and –ve relative convergence?

A
  • Accommodation is constant

- Change vergence demand

49
Q

What do we need to know about +ve and –ve relative accommodation?

A
  • Constant vergence

- Change accommodative demand

50
Q

What are the 3 methods of measuring the AC/A ratio ?

A

1.Heterophoria method

2.Gradient method
Change in convergence response with change in accommodative demand
fixed viewing distance

3.Fixation disparity method
Change accommodative demand with spheres
Measure fixation disparity

51
Q

What is the heterophoria method ?

A

measure deviation at near and distance and need to measure their PD
-caluclatte AC/A ratio-
equation:
pd + (AngleN – AngleD) / Accomm demand)
-if px has eso deviation = put + sign infront of angle
-if px has exo deviation = put - sign infront of angle
-the accom demand is where you holdvyour target- if held at 1/3m at near the accommodative demand would be 3D and if you were told at 50cm the accomdative demand would 1/5= 2.00D
-Makes no allowance for proximal convergence
- PRISM Cover test at near angle.

52
Q

What is the normal ratio for AC/A?

A

3:1 TO 5:1

53
Q

What is the gradient method ?

A

-px wear distance correction
-varying amount of accomodative demand- in 2 ways
1st way- use near gradient method you are going to just vary amount of accomdative demand by putting up +3 to relax the accommodation at near
2nd way- if you are going to do the distance gradient method - you are going to make them accommodate and put up -3.00D and compare deviations with and without it.

Example
Prism Cover Test (PCT) at near (0.33m)
24^ base-out (ESO)- when accommodating 
3^ base-out (ESO) with + 3.00Ds 
- when not accommodating
-accomdative demand - is 3D
  • put in the equation : AC/A = PCT with accm – PCT without accm / Accm demand

AC/A = +24^ – +3/3
= 7:1
-high ratio

54
Q

What to do when observing the near pupil response when accommodating ?

A

-The patients face should be well illuminated
-Keep light on face constant during eye movement
-Isolate near reflex from light response
Use of UV lamp may assist visibility of pupil
Observe pupil response
Rapidly shift fixation
from a distant to near target
Or vice versa
Use detailed target for near and distance
-when px looking into distance- pupils should dialate
-when px looking at near- pupils should constrict

OV2018 binocular vision (15 decks)

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