1.1 Enhanced Orthoptic Assessment Flashcards
Describe the Lees Screen
Two opalescent glass screens
Bisected by a two-sided plane mirror
Each screen has a tangent grid intersected by dots at 15 and 30 degree intervals.
At what angle does each square of the Lees screen subtend?
5 degrees
How is the patient examined on the Lees screen?
Two pointers required.
Patient places pointer with ring around the indicated ‘dot’.
Limitations of the Lees screen
Gross limitation of ocular motility may prevent patient from fixing on the dots. If both eyes are equally affected, Lees has limited value.
Suppression
Does not measure torsion
What is the distance that the Hess Chart is used at?
50cm
Eye under the RED see’s which light?
RED=RED
GREEN=GREEN
Which eye is the fixing eye?
Whichever is under the red goggle
What are the requirements for the Hess?
Foveal fixation
Normal retinal correspondence
Sufficient vision (locate fix’n spots)
Not red/green colour blind
What are the uses of Hess?
Identified affected muscle
Degree of paresis
Extent of development of muscle sequelae
Differentiates between neuro V mechanical and new onset V longstanding
Measurement of deviation
Assesses changes over time
If we apply the uses of Hess, overall why do we use it?
Aid diagnosis in recently acquired incomitant deviations
Good graphical representation of repression, variability, recovery and stability
Can aid determination of most appropriate surgery
Neurogenic V Mechanical
Neuro
- Largest deviation in direction of affected muscle
- Vertical anomalies slope towards normal in opposite positions of gaze
- Development of full muscle sequelae
- Shifted and misplaced appearance
Mechanical
- ‘flattened’ appearance
- Largest deviation in opposite to affected muscle
- Limitation evident in opposing positions of gaze (ie reversal of deviation)
- Looks ‘compressed’
Longstanding V Acquired
Longstanding
- Becomes more concomitant
- Alphabet pattern more likely
Acquired
- More obvious
Interpreting Hess - what does a smaller field indicate and what else do we need to look at?
Smaller field = affected eye
We would then need to look at the deviation in PP and look for the biggest deviation from the normal
What is the main thing to look for in the outer field?
Examine for small under/over actions which may not be evident on the inner field
What does a narrow field, restricted in the opposing direction of movement denote?
A mechanical restriction of OM
What does even sized fields denote?
Either symmetrical limitation of movement in both eyes OR a non-paralytic strabismus
What are the limitations of Hess?
- Only measures 30 degrees from PP and primary defects may be missed
- Cannot measure torsion (unless linear adaption is used)
- Presence of pre-existing deviation with abnormal BSV
What is Herrings law of equal innervation?
Yoked muscles receive the same amount of innervation at the same time
What is Sherrington’s Law of reciprocal innervation?
Any increase in innervation to an agonist muscle must also include a simultaneous decrease in innervation to the antagonist muscle
What is the first of Parks 3 step test?
1 - Identify and measure the deviation in PP to identify 4/8 muscles affected
What is the second of Parks 3 step test?
Assess/measure the vertical deviation on R and L gaze. Identify the position of gaze in which the vertical deviation increases (2/4 muscles identified)
What is the final step of Parks 3 step test?
BHTT @ 3m. Assess/measure vertical deviation with head tilt R and L. Identify in which the vertical deviation increases - affected muscle identified.
What is the field of BSV useful for?
Blow out fractures, Browns syndrome, Graves orbitopathy
Describe what would be expected in a normal field of BSV
Heart shaped, 45-50 degrees from primary. Relatively circular except inferiorly (obscured by nose)
When would it be appropriate to assess the field of BSV?
- Patients complaining of diplopia
- Surgical planning
- compare pre and post op
How can field of BSV be assessed?
- Aimark perimeter
- Octopus
- Goldmann perimeter
What needs to be considered during interpretation and why?
- Position: Area of BSV will be opposite to limitation of eye movements. Position of area of BSV is more important than the size of the area.
- Size: The greater the limitation of OM, the smaller the area of BSV. High fusional amplitudes will result in larger areas of BSV.
- Shape: Narrow fields with diplopia above and below may indicate mechanical restrictions rather than neurogenic palsies.
What are the different ways of measuring torsion?
Synoptophore
Maddox Rod
Double Maddox Rod
Maddox Wing
Adaptation of Lees screen
Awayo cyclo test
Torsionometer
Bagolini Glasses
Objective - fundus photography
