1.1 Enhanced Orthoptic Assessment

Question 1

Describe the Lees Screen

Answer 1

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.

Question 2

At what angle does each square of the Lees screen subtend?

Answer 2

5 degrees

Question 3

How is the patient examined on the Lees screen?

Answer 3

Two pointers required.
Patient places pointer with ring around the indicated ‘dot’.

Question 4

Limitations of the Lees screen

Answer 4

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

Question 5

What is the distance that the Hess Chart is used at?

Answer 5

50cm

Question 6

Eye under the RED see’s which light?

Answer 6

RED=RED
GREEN=GREEN

Question 7

Which eye is the fixing eye?

Answer 7

Whichever is under the red goggle

Question 8

What are the requirements for the Hess?

Answer 8

Foveal fixation
Normal retinal correspondence
Sufficient vision (locate fix’n spots)
Not red/green colour blind

Question 9

What are the uses of Hess?

Answer 9

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

Question 10

If we apply the uses of Hess, overall why do we use it?

Answer 10

Aid diagnosis in recently acquired incomitant deviations
Good graphical representation of repression, variability, recovery and stability
Can aid determination of most appropriate surgery

Question 11

Neurogenic V Mechanical

Answer 11

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’

Question 12

Longstanding V Acquired

Answer 12

Longstanding
- Becomes more concomitant
- Alphabet pattern more likely

Acquired
- More obvious

Question 13

Interpreting Hess - what does a smaller field indicate and what else do we need to look at?

Answer 13

Smaller field = affected eye
We would then need to look at the deviation in PP and look for the biggest deviation from the normal

Question 14

What is the main thing to look for in the outer field?

Answer 14

Examine for small under/over actions which may not be evident on the inner field

Question 15

What does a narrow field, restricted in the opposing direction of movement denote?

Answer 15

A mechanical restriction of OM

Question 16

What does even sized fields denote?

Answer 16

Either symmetrical limitation of movement in both eyes OR a non-paralytic strabismus

Question 17

What are the limitations of Hess?

Answer 17

• 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

Question 18

What is Herrings law of equal innervation?

Answer 18

Yoked muscles receive the same amount of innervation at the same time

Question 19

What is Sherrington’s Law of reciprocal innervation?

Answer 19

Any increase in innervation to an agonist muscle must also include a simultaneous decrease in innervation to the antagonist muscle

Question 20

What is the first of Parks 3 step test?

Answer 20

1 - Identify and measure the deviation in PP to identify 4/8 muscles affected

Question 21

What is the second of Parks 3 step test?

Answer 21

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)

Question 22

What is the final step of Parks 3 step test?

Answer 22

BHTT @ 3m. Assess/measure vertical deviation with head tilt R and L. Identify in which the vertical deviation increases - affected muscle identified.

Question 23

What is the field of BSV useful for?

Answer 23

Blow out fractures, Browns syndrome, Graves orbitopathy

Question 24

Describe what would be expected in a normal field of BSV

Answer 24

Heart shaped, 45-50 degrees from primary. Relatively circular except inferiorly (obscured by nose)

Question 25

When would it be appropriate to assess the field of BSV?

Answer 25

• Patients complaining of diplopia
• Surgical planning
  
  • compare pre and post op

Question 26

How can field of BSV be assessed?

Answer 26

• Aimark perimeter
• Octopus
• Goldmann perimeter

Question 27

What needs to be considered during interpretation and why?

Answer 27

• 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.

Question 28

What are the different ways of measuring torsion?

Answer 28

Synoptophore
Maddox Rod
Double Maddox Rod
Maddox Wing
Adaptation of Lees screen
Awayo cyclo test
Torsionometer
Bagolini Glasses
Objective - fundus photography