Measuring the Ocular Deviation

Question 1

Why should we measure ocular deviation (i.e. why should you bother to measure any tropia or phoria)?

Answer 1

—We need to measure in order to diagnose

—To ensure consistency between examiners

—To Find maximum deviation - in order to decide when to manage

—To Monitor progression – thus we can let px know about improvement/deterioration

—Relate size to fusion range to other clinical features (e.g.. so that if the px has other problems we can know whether it is the strabismus or other problem which is causing worsened diplopia)

—To calculate AC/A ratio

Question 2

How do you measure a patient’s ocular deviation?

Answer 2

—Measurements are taken at:

—At 1/3 metres

—6 meters

—At > 6 meters plus if increases in the distance

— (At all 8 positions of gaze- in the HES - but we aren’t required to do that daily)

—With and without refractive correction

—With and without head posture

Question 3

What are the three subjective methods of measuring ocular deviation?

What are the three objective methods of measuring ocular deviation?

Answer 3

Question 4

In an unreliable patient would you choose objective or subjective methods of measuring ocular deviation and why?

Answer 4

You would choose objective methods as if your patient is unreliable it is likely that their responses will be poor and so not a good basis of diagnosis.

Question 5

Which patients tend to be unreliable when measuring ocular deviation?

Answer 5

Young children ( definitely any below the age of four)

Children and adults with learning difficulties

Patients with communication difficulties e.g. those that have had a stroke and can’t communicate properly.

Question 6

•Which method for measuring ocular deviation is maximally dissociative (i.e. gives maximum angle)?

Answer 6

The Objective Prism Cover Test

Question 7

Why is it important to know which method of measuring ocular deviation is maximally dissociative (i.e. gives the maximum angle)?

Answer 7

It gives an idea of how bad the condition gets and therefore whether they would need treatments such as surgery or not.

Question 8

What is test is the gold standard for measuring ocular deviation?

Answer 8

The objective prism cover test

Question 9

What are disadvantages of the prism cover test?

Answer 9

It requires (a great deal of) patient cooperation thus unsuitable for those with learning difficulties or disabilities.

It is only as reliable as the clinician carrying out the test.

Question 10

What does the Prism Cover Test (PCT) measure?

Answer 10

PCT measures TOTAL deviation (manifest & latent deviation combined)

Question 11

What is the correct accommodative target for the prism cover test?

Answer 11

—The line above weakest eye e.g. RE: 6/18, LE: 6/12 thus we use 6/24

—But spot light if they can’t see 6/60 letter

Question 12

Before carrying out a PRISM cover test what would you have initially carried out?

Answer 12

A cover test should have been carried out.

Question 13

How do you carry out a Prism Cover Test (PCT)?

Answer 13

Question 14

In the Prism Cover test why do you put the prism in the direction that you do?

Answer 14

Look at notes for diagramatic answer.

But essentially by placing the prism in the direction opposite to the eye’s deviation you move the ‘false image’ to where the real one is.

Question 15

What are the steps to carrying out a prism cover test?

Question 16

When carrying out the prism cover test why do you do the alternating cover test SLOWLY (2)?

Answer 16

As it makes it easier to determine what’s happening as the clinician.

If your px has poor vision it gives them time to focus on the target.

Question 17

What are the advantages and disadvantages of the prism cover test?

Answer 17

(By angle we mean direction of the base)

Question 18

When is a Simultaneous Cover Test (SPCT) used and what does it measure?

Answer 18

It is used in manifest strabismus with a latent component.

The SPCT test measures ONLY manifest deviation.

Question 19

How do you carry out a Simultaneous (Prism) Cover test (SPCT)?

Answer 19

—Perform cover test to determine type & estimate angle of deviation

—Prism of estimated strength paled before deviated eye while occluder simultaneously covers fixing eye (cover/uncover cover test)

—Keep increasing strength until neutral movement achieved (to confirm)

Question 20

What are the three tests for estimating the angle of deviation via corneal reflections?

Answer 20

—Bruckner

—Hirschberg test

—Krimsky test

Question 21

What is the Bruckner test for estimating the angle of deviation via corneal reflections?

Answer 21

It is a red reflex examination for neonatal, infant, and children.

It is more of a screening test. (Use ophthalmoscope at 0)

If red reflex is slightly less bright than the other you want to go ahead and check if it’s due to prescription and once that’s been sorted you can look for strabismus.

Question 22

How do you carry out the Hirschberg Test and what are you looking for?

Answer 22

—Patient fixes on pen torch at 33 cm

—Corneal reflections noted in fixing eye and compared with the other eye

—Displacement (of the corneal reflection is) estimated. The rue of thumb here is 1mm displacement = 20-22Δ deviation approximately

Question 23

How do you carry out a Krimsky test and when do you carry it out?

Answer 23

—Patient fixes on light at 33cm

—Used when you have manifest deviation and fairly poor vision in one eye

—Corneal reflection noted in both eyes

—Estimated prism placed in front of fixing eye

—Base opposite to deviation

—Strength increased until the corneal reflexes in deviated eye equal to the position in fixing eye initially

—Can be used with prism before deviating eye (prism reflection test)

Question 24

How do you carry out a prism reflection test and when is it carried out?

Answer 24

Used when you have manifest deviation and fairly good vision in both eyes

Essentially you are placing the prism in front of the deviated eye. You then increase the prism strength until the corneal reflection in the deviated eye is approximately equal to where the cornel reflection is in the fixing eye.

Question 25

What are the advantages and disadvantages of using corneal reflection to measure ocular deviation?

Answer 25

Question 26

How do you carry out a Subjective Prism Cover Test?

Answer 26

—Head straight- with the target same size as before

—

—Carry out Cover Test

—Place prism of estimated strength before:

—Strabismic eye in manifest deviation

—Either eye if latent

—The base direction is opposite to deviation e.g. with RSOT Base Out is placed in front of RE

—Carry out an alternating cover test

—Ask the patient if they notice image moving from:

-Side to side or Up to down

—Find prism strength to neutralise movement of images as cover is moved from one eye to the other

[If image moves with the ocluder its exo if it moves opposite to the occluder its eso)

—Make deviation reverse then record prism before reversal

—Useful in small symptom producing vertical deviation

Question 27

How do you carry out a Maddox rod test?

Answer 27

–High powered cylinders blur spot of light into streak at 90 degrees to the direction of grooves (px sees 90 degrees to filter placed infront of their eyes)

—Other eye views spot light

—Traditionally red but sometimes clear or blue

Question 28

What are the advantages and disadvantages of the Maddox Rod test?

Answer 28

Question 29

What test can be used to test for cyclo-deviations?

Answer 29

The Maddox double rod test

Question 30

How do we carry out the Maddox Double rod test and what are we looking for?

Answer 30

Question 31

How do you carry out the Maddox Wing Test?

Answer 31

—Torsion indicated if red horizontal arrow not parallel with the white horizontal grading scale

—Patient asked to adjust arrow themselves until it is parallel

Question 32

What are the advantages and disadvantages of the Maddox Wing test?

Answer 32

Question 33

True or false- positive lenses stimulate accommodation.

Answer 33

FALSE - it’s minus lenses that stimulate accommodation (and therefore convergence)

Question 34

When would spectacles not impact ocular deviation?

Answer 34

For Pxs that don’t experience accommodation i.e. our presbyopes.

Question 35

How can correction affect ocular deviation?

Answer 35

Because lenses affect accommodation e.g.

Minus lenses stimulate accommodation and therefore convergence.

Thus if someone is exo-deviated and wears minus lenses you wouldn’t get the full measure of their ocular deviation (you would have underdiagnosed)

Question 36

Answer 36

6/60

This isn’t the prism cover test it’s the prism fusion range test where the target for everybody is 6/60.

Question 37

Answer 37

Maddox Double Rod