Common Hess Charts in OSE 
and Final MRCOphth
The following Hess charts are the most commonly encountered in the examination. 
Neurogenic causes
  • Third nerve palsy
  • Fourth nerve palsy
  • Sixth nerve palsy
Mechanical causes
  • Obital floor fracture
  • Duane's syndrome
  • Brown's syndrome
  • Thyroid eye disease
s s s s
The following steps are useful in interpreting a Hess chart:

1. Which is the abnormal field? The chart with the small field is the abnormal one.

2. Is the field compressed? If compressed, consider mechanical causes

3. Which muscle is underacting? The greatest negative or inward displacement 
     represents the primary underaction

4. Which muscle is overacting? The muscle with positive or outward displacement 
     indicates an overaction.
Click on the following pictures to test your understanding of Hess chart.
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