Accommodation and Convergence

Question 1

What is the definition of convergence?

Answer 1

Simultaneous rotation of the eyes inwards

Question 2

How may we measure the near point of convergence?

Answer 2

[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

Question 3

When trying to test for near point convergence do we get Pxs to wear their correction?

Answer 3

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]

Question 4

Why do we do the RAF rule test three times?

Answer 4

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).

Question 5

How do you conduct the push up and back test using an RAF rule?

Answer 5

—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

Question 6

What is normal near point convergence for a pre-presbyope?

Answer 6

10cm or less with ease

Question 7

What is a normal near point value for a presbyopic patient on an RAF rule?

Answer 7

Around 15 cm or less with ease

Question 8

How can you test convergence subjectively and objectively?

Answer 8

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

Question 9

What is the definition of convergence?

Answer 9

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

Question 10

What is the definition of Accommodation?

Answer 10

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

Question 11

What are the ways in which we can measure accommodation?

Answer 11

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

Question 12

What’s the method for finding the near point of accommodation using an RAF rule?

Answer 12

—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

Question 13

What does amplitude of accommodation (AoA) vary with?

Answer 13

Age

(The older you get the lower AoA gets).

Question 14

How can you work out what a normal AoA for a particular aged px is?

Answer 14

Look at the RAF rule it notes what is normal and for what ages.

Question 15

How do you record results from an AoA test?

Answer 15

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’

Question 16

How do you carry out a test for near amplitude of accommodation using minus lenses?

Answer 16

—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

Question 17

Why is the minus test for determining amplitude of accomodation not used in high street practice?

Answer 17

It takes a significantly long amount of time - it can take a px a good ten seconds to make the target clear before moving onto the next lens

Question 18

What is accommodative facility?

Answer 18

Basically the ability of the eye to change accommodative states i.e. go from relaxing accommodation to stimulating it.

Question 19

What are we testing for when looking at accommodative facility?

Answer 19

Essentially the speed of change in accommodation and Rapid refixation from near to distance viewing

Question 20

How do we test accommodative facility using flipper lenses?

Answer 20

Px is wearing full Rx to start with and you note the lowest line they can read.

You then use flippers (make sure you are aware of the power of the fippers - these come in many different powers).

Put a minute timer on and now place the flipper infront of the eyes.

As soon as the patient says the line is clear again flip to the other side of the lenses (i.e if they were using the positive side of the flipper use the negative side now).

As soon as the patient says the line is clear again flip to the other side again.

What you want to be recording is how many cycles ( flips from one lens to the other) the px can do in a minute.

Question 21

When recording results of accommodative facility using flipper lenses what must we record?

Answer 21

—Whether Px is wearing Rx

—Strength +/- flippers

—No. of cycles /minute

—Size of print

Question 22

When testing accommodative facility in a child/young adult what is a normal number of cycles per minute?

Answer 22

At +2.00, 9 – 11 cycles / minute

Question 23

What is the disadvantage of using subjective methods to test for accommodation?

Answer 23

—An unreliable endpoint is given by Pxs such as children or those with learning difficulties.

—Large difference between stimulus and response accommodation – basically in real life even though a target may take 3D of accommodation, humans are lazy and will only accommodate 2.5D.

• depth of field
• small pupils, increased depth of field

—Subjective criteria – some patients will tell you when the target just blurs whilst others will tell you when it blurs so much they can’t read the target so wording becomes really important.

Question 24

How do you carry out Monocular Estimation Method (MEM) dynamic retinoscopy?

Answer 24

—Px Wears distance Rx

—Target at same distance as ret.; normally 40cm (target is hooked around the ret)

—Patient fixates on detailed target

—Neutralisation occurs when back focal plane of eye conjugate with back focal plane of retinoscope - i.e. when you see reversal from the ret.

—You get a max of two swipes - anymore and the eye will begin to relax and not give a proper reading (remember humans are lazy)

• If you see a with movement from the ret – Accommodative Lag is occuring
• If you see an Against movement from the Ret– Accommodative lead is occuring.

—Neutralise:

—Using appropriate spheres in one meridian only VERY BRIEFLY

[You are only testing one meridian]

Question 25

How do you carry out the NOTT method of dynamic retinoscopy?

Answer 25

Question 26

What is a normal lag value from NOTT dynamic retinoscopy?

Answer 26

Up to 0.75 dioptres

Question 27

What is the definition of the AC/A ratio?

Answer 27

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

Question 28

If a patient had an AC/A ration of 4:1 what does this mean?

Answer 28

Theoretically when that patient accomodated by 1 dioptre their eyes pull in by four.

Question 29

Theoretically if a patient had 12 dioptres of exotropia and we worked out that their AC/A ratio is 4:1 what prescription lenses would we give them?

Answer 29

So we know if they are exotropic we want to make their eyes converge.

Minus lenses cause convergence.

If their eyes are out by 12 dioptres and we know for every 1 dioptre of rx we give them that their eyes move by 4 we would want to give them 3.00D of rx in total.

Final Rx is -3.00DS.

Question 30

In positive and negative relative relative convergence what is constant and what do we manipulate/change?

Answer 30

—Accommodation is kept constant

—We change vergence demand

Question 31

In positive and negative relative accommodation what do we keep constant and what do we change?

Answer 31

—We keep a Constant vergence

—We Change accommodative demand

Question 32

What are the three methods for measuring the AC/A ratio?

Answer 32

—Heterophoria method

—Gradient method:

• Where we measure change in convergence response with change in accommodative demand
• in this method there is a fixed viewing distance

—Fixation disparity method:

—In this method we change accommodative demand with spheres

—And Measure the fixation disparity

Question 33

What is the Heterophoria method for calculating AC/A ratio?

Answer 33

—Px Wears distance Rx

—Difference in angle of deviation (phoria or tropia) on near and distance fixation is measured

• Thus you measure:
• Pd (cm)
• angle of deviation on distance fixation
• angle of deviation on near fixation

—Calculate AC/A:

The formula is :

pd + (AngleN – AngleD) / Accommative demand)

Accommodative demand is the distance at where you held the target converted into dioptres

—To know the signs –> Take eso or as +ve and exo as -ve

[This method makes no allowance for proximal convergence]

Question 34

Calculate the AC/A ratio from the heterophoria method if the px is Exophoric and has the following readings:

—Distance viewing: 2Δ XOP

—1/3rd m viewing: 8Δ XOP

—eso is +ve, exo is -ve

—pd 6.4 cm

Answer 34

Question 35

What is the normal range of the AC/A ratio?

Answer 35

3:1 to 5:1

Question 36

How does the gradient method for working out AC/A work and how do you carry it out?

Answer 36

In the AC/A gradient method you are varying the amount of accommodative demand.

This can be done at EITHER near or distance.

—To Calculate at Near:

-Compare Prism Cover Test (PCT) with + 3.00Ds binoc and without

—To Calculate at Distance:

-Compare Prism Cover Test (PCT) with -3.00Ds binoc and without

Question 37

What is the formula to calculate AC/A ratio from the gradient method?

Answer 37

Question 38

How would you calculate the AC/A ratio from the gradient method for the following px:

—Prism Cover Test (PCT) at near (0.33m):

—24^ base-out (ESO)

—3^ base-out (ESO) with + 3.00Ds

Answer 38

Question 39

When doing any calculations what sign does Eso have and what angle does Exo have?

Answer 39

Eso is always taken as a +ive

Exo is always -ive.

Question 40

Define Miosis

Answer 40

Miosis, or myosis, is excessive constriction of the pupil.

Question 41

When pupils converge do they miose or dilate?

Answer 41

They miose - i.e. when pupils look at things near you see them constrict.

Question 42

How can we see pupils responses to convergence?

Answer 42

[A near pupil response - is that it constricts when focussing at near]