Measuring Angle of Deviation Flashcards
What do we need to note when measuring angle of deviation?
1) Deviation of visual axes
2) Signs of possible oculomotor defect
3) AHP
4) Craniofacial abnormality
5) Abnormal eyelid shape and position
What is the Hirschberg’s test?
Corneal reflections are nasal, giving positive angle kappa of 3 degrees in an emmetropic eye. In small angle strabismus it’ll appear normal but off-centre pupil is approximately 15 degrees, off-centre iris is approx 30 degrees and off-centre on sclera is approx 45 degrees.
How do you do the Hirschberg’s test method?
Penlight at 33cm, observe corneal reflections, compare reflections. A 1mm displacement is approximately 7-12 degrees deviation.
When would you use the Hirschberg’s test?
To measure the angle of deviation in young children, those with poor co-operation, low VA, if unable to fixate and in a manifest deviation
What are the drawbacks of the Hirschberg’s test?
It’s not accurate, it cannot measure small deviations and is not for latent deviations. As it’s using a light it is a non-accommodative target and only used at near. It doesn’t involve dissociation so is not showing total deviation.
What is the prism reflection test/Krimsky? and what is the method?
A way to measure angle of deviation. It is done with and without glasses (if necessary) with a penlight at 33cm, observe the corneal reflections and then place a prism over the fixing eye (bar or loose, base in opposite direction to the deviation or apex in the same direction of the deviation) and increase the prism until the reflections appear symmetrical.
The eye behind the prims will move to maintain fixation and, due to Hering’s law, the squinting eye will make a conjugate movement.
When should you use Krimsky/Prism Reflection Test?
When the individual has low VA, is a young child, has poor co-operation, is unable to take up fixation and for manifest deviations
What are the limitations to the Krimsky/Prism Reflection Test?
It’s not accurate and is difficult to measure small deviations, it’s not for latent deviations and is non-accommodative target only (light), at near only and doesn’t involve dissociation
How many dioptres will 1 prism dioptre shift an image at a distance of 1 meter?
1cm
How many degrees is in 1 prism dioptre?
0.57 degrees
How many prism dioptres is in 1 degree?
1.75 prism dioptres
What’s the method for a prism cover test?
Used to measure the size of a deviation.
1) Fixate at 33cm either c/glasses or s/glasses
2) Alternate cover test completed to assess the approximate size and note the preferred eye in manifest deviations. If it’s concomitant then PCT can begin with either eye.
3) Introduce the appropriate prism in front of the deviating eye
4) Perform an alternate cover test adjusting the prism strength until no movement of the eye is under the prism when the other eye is covered
5) Once neutralised you go past this point until the reversal movement is seen (e.g. cause an exo in an eso deviation) to confirm the maximum angle
6) Reduce again to ensure no movement is seen
7) Record in PD
Why must you be slow and give patients time to fixate during the prism cover test?
Must prevent fusion through continued use of ACT
In amblyopic patients how do you place prisms during the prism cover test?
High powered prisms can reduce clarity of vision, hard for amblyopic patients to fixate so can place the prisms in front of the better eye or can split for large angles (but can lead to some inaccuracy - do not do for if correcting both horizontal and vertical deviations)
What are the pros of the prism cover test?
It’s performed in free space, the comparison can be done for different distances, can be done in >2yo and can be done in both latent or manifest deviations
What are the cons of the prism cover test?
Have to be co-operative, need to take central fixation and thus have reasonable VA, must be co-operative, have to prevent fusion and if doing prisms over both eyes then they must convert the results
What is the simultaneous prism cover test?
The total deviation in manifest and latent deviations are seen in some cases of microtropia or larger deviations with abnormal gross BSV
How do you complete the simultaneous prism cover test?
Patient fixes at 33cm, the prism is placed over the deviating eye and the occluder over the fixing eye but are introduced at the same time (simultaneously)
Aim to neutralise the movement of squinting as the fixing eye is covered
What are the pros of the simultaneous prism cover test?
Can view the manifest deviation with latent deviation, it’s performed in free space, the comparison can be done for different distances, can be done in >2yo
What are the cons of the simultaneous prism cover test?
Co-op patient required and they have to take up fixation
What are the tests used to measure deviations?
Hirschbergs
Krimsky / Prism Reflection Test
Prism Cover Test
Simultaneous PCT
Synoptophore
Maddox Rod
Double Maddox Rod
Torsionometer
Awaya Cyclo-Test
Lees Screen with linear Pointer
Ophthalmoscopy/Fundus Photography
Bagolini Striated Glass Test
What is the Maddox Rod?
A way of measuring deviations. Coloured plastic or glass containing series of high ridges made up of high strength cylindrical lenses that converts a spotlight into a coloured streak of light that’s perpendicular to the rod.
What is the method for using the Maddox Rod?
1) In a slightly darkened room with the spotlight at the required distance
2) The Maddox Rod is held with cylinder axes horizontal over the deviating/non-fixing eye
3) Ask which side the person sees the vertical red line
4) Prism is held in front of the rod and strength adjusted until the line passes through the light
5) Repeat on the fixing eye
6) Record prism strength
7) Repeat with rod held vertically for vertical deviations
May be a difference with torsion so need to ask the patient if the line is exactly vertical or not
What are the pros of the Maddox Rod?
- Small deviations measurable especially vertical that can be difficult to see on PCT
- Can detect torsion with co-operative
- Dissociation
- Near or distance
- c/gls or s/gls
What are the cons of the Maddox Rod?
- Must have normal retinal correspondence
= Can’t measure small-angle horizontal strabismus in ARC - Can’t do larger deviations or accommodation (as it can’t be controlled)
If a patients right eye is covered and they see the vertical line to the left what projection is this?
Exo projection = heteronymous projection
In the horizontal plane during the Maddox Rod what does an exodeviation or esodeviation look like? What about for hyper and hypo?
In the horizontal plane testing, a homonymous diplopia indicates esodeviation, and heteronymous diplopia indicates exodeviation. In the vertical plane testing, the streak seen by the hyperdeviated eye appears lower than the light and vice versa for the hypodeviated eye
What is the Maddox Rod Tangent Scale?
It’s used in the far distance for the patient to read off the scale where they see the line
At what angle do the oblique muscles insert at?
51 degrees to the visual axis
What measurements can you use to measure cyclodeviations?
- Double Maddox Rod
- Synoptophore with Maddox Slides (white)
- Torsionometer
- Awaya Cyclo-Test
- Lees Screen with linear Pointer
- Ophthalmoscopy
How does the Double Maddox Rod work?
It’s a subjective measure of torsion. Has them over each eye so the individual sees 2 horizontal lines.
1) Fixate on a spotlight
2) Use vertical prism to separate the 2 lines using a 6PD base down prism if no vertical deviation is present
3) Person adjusts orientation in trial frame until the images are straight and parallel
4) Read degrees which is the amount of torsion
5) Ensure straight head (not AHP) as need to be exactly horizontal
6) Red before the right eye which is seen below the white light on the white
What must you be aware of with the Double Maddox Rod?
- Allow time for dissociation in latent strabismus
- 1/3m and 6m
- Measure in different positions of gaze
- Diagnostic positions
- Unsuccessful more than 10-12 degrees from the PP(?)
- Can’t use in deviations >20 degrees of vertical deviation
- Can recover from suppression by quickly covering and uncovering the fixing eye
What are the subjective measures of measuring an angle of deviation?
Synoptophore & Maddox Rod
How do we use the synoptophore for measuring deviations?
Must put the cross before the fixing eye (the cross and the bun). After measures of horizontal and vertical deviations the ‘bun’ should be rotated until it makes a hot-cross bun. Read off the torsion scale.
What are the benefits of using a synoptophore in measuring angle of deviation?
- 9 positions of gaze
- Up to 30 degrees from PP but usually 20 degrees
- Repeatable
- Good in larger horizontal or vertical
How is the Torsionometer used for measuring angle of deviation?
1) Rotate green line maximally
2) Move the green until it is parallel with the red
3) Explain that 1 line may look higher than the other
4) Reverse the plate and read from the scale in degrees
5) Larger incyclo. measured via reversing the goggles (red over right for excyclo)
Can measure different gaze positions but the plate must be perpendicular to the visual axes
Larger vertical deviations must be corrected first
How is the Awaya Cyclo-Test used for measuring deviations?
- It’s presented in book form with 13 pairs of half moons. The red half moon is upright on all figures.
- Red moon on the right and green moon on the left with a 10mm gap between them
- Each plate increases with 1 degree steps with a maximum of 12 degrees for the 12th pair
- Red goggles goes in front of the right eye
- Ask the patient if these are parallel on the first pair
- If the green is tilted clockwise this is an intorsion but if tilted anti-clockwise it’s an extorsion
- If there is an intorsion then reverse the glasses and repeat the procedure but if extorted continue with viewing the succeeding pair until, they look parallel
- If there isn’t a cyclodeviation then figure 0 half-moons will look straight
What is the bagolini striated glass test?
Vertical striations show 2 horizontal line images. Vertical prism to separate. This is closer to normal seeing but they may continue to suppress.
What is the Lees Screen with Linear Pointer?
Used to measure torsion. Has 2 opalescent glass screens at right angles and is bisected by a 2-sided plane mirror. The mirror reverses the image so intorted image is extorted by mirror in exocyclotorsion and they plot what the eye is doing. Patient and examiner have pointers.
What is ophthalmoscopy/fundus photography?
An objective measure of torsion. Fovea usually 0.3 disc diameters below horizontal line through centre of optic disc (but varies up to 0.25). Greater is abnormal and so a cyclodeviation.
What does an incyclo and exocyclo deviation look like in a fundus photo?
High fovea = incyclo
Low fovea = excyclo
What tests for measuring deviation are good for reduced VA?
Corneal Reflections, Prism Reflection Test and Synoptophore
What tests for measuring deviation are good for people with limited co-operation?
Corneal Reflections and Prism Reflection Test
What tests for measuring deviation require simultaneous perception?
Maddox Rod, Maddox Wing, Lees Screen and Synoptophore (sometimes)
What tests for measuring deviations can be done with the 9-positions?
Maddox Rod, Prism Cover Test, Synoptophore and Lees Screen
How do you record the different tests of measuring deviations?
Write down examples of each
If the RE has the maddox rod and the line is seen downwards, what deviation is this? What base do we use to correct?
Hyper - Base Down
If the RE has the maddox rod and the line is seen upwards, what deviation is this? What base do we use to correct?
Hypo - Base Up
What are the different synoptophore slide sizes?
Foveal
Macular
Paramacular
Peripheral
What are the different synoptophore slide colours for?
Red = Simultaneous Perception
Green = Fusion
Yellow = Stereopsis
White = Maddox slides
Which way (from the patient’s perspective) would you move the arm of the synoptophore in an Eso deviation during Simultaneous Perception?
Move it forwards from the patient’s perspective
