1.1 Enhanced Orthoptic Assessment Flashcards
Describe a Lees Screen
Two opalescent glass screens, bisected by a two-sided plane mirror
What are Lees screen measurements
Inner field - 15 degrees
Outer field - 30 degrees
Each square - 5 degrees
What are the limitations of Lees screen
OM may prevent the patient fixing on some dots if there is a gross limitation.
Suppression will stop the test from working.
There is no measurement of torsion.
What is the testing difference for a Hess Chart
50cm
How do hess red/green goggles work when red light is being controlled by examiner
Eyes are dissociated by goggles
Eye under red goggle sees red light - acts as fixing eye.
What are requirements for a hess chart examination
Foveal fixation
Normal retinal correspondence
Sufficient vision in either eye - to locate fixation spots
Patient should not have red/green colour blindness.
Positives of Hess Chart
Excellent of aiding diagnosis in recently acquired incomitant deviations.
Good graphical representation of repression, variability, recovery and stability.
Can aid determination of most appropriate surgery.
What are the uses of a Hess Chart
Determine which muscle is affected
The degree of paresis
Extent of muscle sequelae development
Differentiates between new onset V longstanding and mechanical V neurogenic
Assesses measurement of deviation
Assesses change over time
What are key signs of a neurogenic Hess Chart
Largest deviation in direction of affected muscle
Vertical anomalies slope towards the normal in opposite positions of gaze
Development of full muscle sequelae
Shifted and misplaced appearance
What are key signs of a mechanical Hess Chart
‘Flattened’ appearance
Largest deviation in opposite to affected muscle
Limitation evident in opposing positions of gaze (eg reversal of deviation)
Looks ‘compressed’
Differential diagnosis - Longstanding V Acquired
Longstanding becomes more concomitant
Recently acquired defect is more obvious
Alphabet pattern more likely in longstanding deviations.
When interpreting Hess charts, how do you tell which eye is affected?
The chart with the smallest field is the affected eye (look at the deviation in PP).
On the same chart look for the biggest deviation from the normal.
Equal sized fields denotes to either symmetrical limitation of movement in both eyes or non-paralytic strab.
What are the limitations of a Hess Chart
Only measures 30 degrees from PP and subtle defects may be missed
Cannot measure torsion unless linear adaptation is used
Presence of pre-existing deviation with abnormal BSV
What is Herrings Law
The law of equal innervation. Yoked muscles receive the same amount of innervation at the same time.
What is Sherringtons Law
The law of reciprocal innervation. Any increase in innervation to an antagonist muscle must also include a simultaneous decrease in muscle innervation to the antagonist muscle.
