Binocular Vision Competency 8.7

Competency 8.7: The ability to manage a patient presenting with an incomitant deviation

An incomitant deviation is caused by an imbalance of the extraocular muscles and as such, varies in size according to gaze position.  Such deviations can be considered as falling into three categories, in order of occurrence:

  • Neurogenic – caused by an interruption to the nerve supply between the brainstem control centres and the extraocular muscles
  • Mechanical – caused by a physical restriction to the movement of the eye within the orbit
  • Myogenic – caused by a defect of the muscle itself, either a change to the structure or function of the muscle tissue or to the synaptic terminal of the incoming nerve.

Another important differentiation is that between a recent onset and long-standing deviation as the management is often very different for either type.  For example, a sudden onset neurogenic palsy will require prompt medical investigation whereas a congenital mechanical restriction may require no intervention at all.  Consideration should also be given to the short-term management of patients prior to onward referral, for example those who present with diplopia with a very recent onset deviation and are not suitable for prisms.

In order to differentiate between the different types of incomitant deviation, careful assessment of ocular motility is required, with particular attention given to the presence and extent of muscle sequelae.

Best Form Evidence

For this competency you should be able to produce at least one Patient Record of a patient with an incomitant deviation.  Additional evidence will come from Questioning and Case Scenarios or Role Play.

The examiner will expect to see:

  • Thorough case history, with particular consideration given to the onset and duration of symptoms, differentiating between a recent onset and longstanding deviation
  • Accurate recording of ocular deviation and ocular motility in all positions of gaze
  • Appropriate management strategy, including optical or non-optical management for symptomatic deviations and onward referral if required
  • Proper advice given with regard to driving with diplopia, if appropriate
  • Failure to identify recent onset acquired deviation
  • Inappropriate referral, in particular failure to refer recent onset deviations for investigation
  • Inappropriate use of prisms in highly incomitant deviations
  • Nerve pathways and muscle innervation laws
  • Actions of extraocular muscles in isolation and in synergistic/antagonistic pairs
  • Common aetiologies of each type of deviation
  • Proper detection of incomitant deviation with appropriate management strategy dependent on type and onset
  • Referral of new or worsening incomitant deviation for medical investigation

Unacceptable Evidence

  • Failure to identify recent onset acquired deviation
  • Inappropriate referral, in particular failure to refer recent onset deviations for investigation
  • Inappropriate use of prisms in highly incomitant deviations

What to study

  • Nerve pathways and muscle innervation laws
  • Actions of extraocular muscles in isolation and in synergistic/antagonistic pairs
  • Common aetiologies of each type of deviation

Pass/Fail criteria

  • Proper detection of incomitant deviation with appropriate management strategy dependent on type and onset
  • Referral of new or worsening incomitant deviation for medical investigation

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