Accommodation and Convergence Flashcards
What is the definition of convergence?
Simultaneous rotation of the eyes inwards
How may we measure the near point of convergence?
[This differs by country].
Pen to nose:
- Basically move pen towards the Px’s nose until you see their pupils moving in to converge
- An inaccurate technique
- Provides an estimate of the n.p.c.
RAF rule:
- Dot provides a fixation point (the line with the dot on it picture)
- Single high contrast line helps recognition of diplopia (i.e you ask when that line splits into two)
- Use cm scale for measurement
When trying to test for near point convergence do we get Pxs to wear their correction?
Blurring of the target is not relevant (as convergence isn’t the same as accommodation – but at the same time if the target becomes so blurred that the patient cannot actually see it – they can’t do the test) Thus rule of thumb is:
- high hypermetropes should be wearing glasses
- presbyopes should be wearing glasses
- Moderate to high myopes should wear spectacles
-But Bear in mind for myopes:
- Base in prisms due to –ve lens edge will assist convergence
- Lens edge and frame contours may obscure target
[Essentially if your px requires correction to see near they should keep it on durring the test]
Why do we do the RAF rule test three times?
To make sure we can determine if any results are due to convergence fatigue ( which would mean the result is worse- basically your eyes get tired).
How do you conduct the push up and back test using an RAF rule?
Push target towards patient using RAF rule
At a rate of roughly 1-2cm/second
Record break point (when they experience diplopia- two lines)
Bring target away from patient
watch for fusion (i.e. target going back to normal)
Record recovery point
Repeat x 3
What is normal near point convergence for a pre-presbyope?
10cm or less with ease
What is a normal near point value for a presbyopic patient on an RAF rule?
Around 15 cm or less with ease
How can you test convergence subjectively and objectively?
Test subjectively- i.e uses patient response:
When patient reports diplopia
Stress to the patient that you aren’t interested in when the line blurs rather when the line becomes double.
Test objectively- uses clinician (normally done on children)
Watch the patients eyes for convergence to break
Note the eye which diverges first
Note the distance and whether they were able to maintain convergence
Note whether diplopia was noticed
What is the definition of convergence?
The ability to change the convexity of the crystalline lens in order to obtain a clear image of a near object
What is the definition of Accommodation?
The ability to change the convexity of the crystalline lens in order to obtain a clear image of a near object
What are the ways in which we can measure accommodation?
1.Measuring Accommodative amplitude or range:
This can be done via Finding Near point using an RAF rule
Or by Using Minus lenses (significantly long method)
2.Measuring Accommodative facility
This can be measured via Flipper lenses
3.Measuring Accommodative lag or lead
Via Dynamic retinoscopy- there are two methods of carrying out dynamic ret:
- Monocular Estimation Method
- Nott Method
What’s the method for finding the near point of accommodation using an RAF rule?
Test monocularly and binocularly
Ensure FULL distance Rx is worn:
-Maximum +ve or least -ve
Find nearest point of clear vision (here we are focussed on when image becomes blurred)
- measure in cm and convert to dioptres (if scale not given)
- use dioptric scale
Target for the test is:
N5 or smallest visible print or target
Technique:
- 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
Select smallest visible line of text:
-printed text is a more demanding target than single letter presentation
For Difficult patients (e.g. presbyopes):
If Amplitude of the px is below 2.00 DS (at 50 cm) i.e. your presbyopic patients:
Start them off with a binocular near add
e.g. +2.00 DS
Then do the test and find their near point and subtract the add you gave them at the start from the final result final result
What does amplitude of accommodation (AoA) vary with?
Age
(The older you get the lower AoA gets).
How can you work out what a normal AoA for a particular aged px is?
Look at the RAF rule it notes what is normal and for what ages.
How do you record results from an AoA test?
State which test you used:
State whether you are carrying it out Binocularly or Monocularly:
State whether you are carrying out with correction or not
State how many repeats you did
State Units:
e.g. ‘AoA RAF:
Binoc With Rx: 10.00D x3
Monoc With Rx: RE 8.00D x3 , LE 8D x 3’
How do you carry out a test for near amplitude of accommodation using minus lenses?
Ensure px is wearing full refractive correction
Place Target near card at 40cm
Occlude One eye
Place Negative lenses in front of eye
Which increased in 0.25Ds steps
Encourage patient to make the print clear
The End point is when letters can not be made clear
Repeat for other eye and binocularly