Measuring the Ocular Deviation Flashcards
Why should we measure ocular deviation (i.e. why should you bother to measure any tropia or phoria)?
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
How do you measure a patient’s ocular deviation?
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
What are the three subjective methods of measuring ocular deviation?
What are the three objective methods of measuring ocular deviation?
In an unreliable patient would you choose objective or subjective methods of measuring ocular deviation and why?
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.
Which patients tend to be unreliable when measuring ocular deviation?
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.
•Which method for measuring ocular deviation is maximally dissociative (i.e. gives maximum angle)?
The Objective Prism Cover Test
Why is it important to know which method of measuring ocular deviation is maximally dissociative (i.e. gives the maximum angle)?
It gives an idea of how bad the condition gets and therefore whether they would need treatments such as surgery or not.
What is test is the gold standard for measuring ocular deviation?
The objective prism cover test
What are disadvantages of the prism cover test?
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.
What does the Prism Cover Test (PCT) measure?
PCT measures TOTAL deviation (manifest & latent deviation combined)
What is the correct accommodative target for the prism cover test?
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
Before carrying out a PRISM cover test what would you have initially carried out?
A cover test should have been carried out.
How do you carry out a Prism Cover Test (PCT)?
In the Prism Cover test why do you put the prism in the direction that you do?
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.
What are the steps to carrying out a prism cover test?
When carrying out the prism cover test why do you do the alternating cover test SLOWLY (2)?
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.
What are the advantages and disadvantages of the prism cover test?
(By angle we mean direction of the base)
When is a Simultaneous Cover Test (SPCT) used and what does it measure?
It is used in manifest strabismus with a latent component.
The SPCT test measures ONLY manifest deviation.
How do you carry out a Simultaneous (Prism) Cover test (SPCT)?
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)
What are the three tests for estimating the angle of deviation via corneal reflections?
Bruckner
Hirschberg test
Krimsky test
What is the Bruckner test for estimating the angle of deviation via corneal reflections?
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.
How do you carry out the Hirschberg Test and what are you looking for?
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
How do you carry out a Krimsky test and when do you carry it out?
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)
How do you carry out a prism reflection test and when is it carried out?
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.
What are the advantages and disadvantages of using corneal reflection to measure ocular deviation?
How do you carry out a Subjective Prism Cover Test?
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
How do you carry out a Maddox rod test?
–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
What are the advantages and disadvantages of the Maddox Rod test?
What test can be used to test for cyclo-deviations?
The Maddox double rod test
How do we carry out the Maddox Double rod test and what are we looking for?
How do you carry out the Maddox Wing Test?
Torsion indicated if red horizontal arrow not parallel with the white horizontal grading scale
Patient asked to adjust arrow themselves until it is parallel
What are the advantages and disadvantages of the Maddox Wing test?
True or false- positive lenses stimulate accommodation.
FALSE - it’s minus lenses that stimulate accommodation (and therefore convergence)
When would spectacles not impact ocular deviation?
For Pxs that don’t experience accommodation i.e. our presbyopes.
How can correction affect ocular deviation?
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)
6/60
This isn’t the prism cover test it’s the prism fusion range test where the target for everybody is 6/60.
Maddox Double Rod
