Cases for finals #7 – Examination

Speech – normal

HMF – normal

Cranial nerves

  • VA left – Perception of Light (PoL) only
  • VA right – 6/5
  • left pupil dilated
  • rest normal

Limbs – normal

Do the findings support optic neuritis? In a word, YES.

What bedside test might be useful?

The swinging torch test, used to show a Marcus Gunn pupil or, as it is more commonly called, “Relative Afferent Pupillary Defect” (RAPD), is what we are after here.

Console yourself with the fact that nobody really has an clear idea of what Marcus Gunn did as a test, and if that is what we do now – just trust me that, when the optic nerve on one side is damaged, and you swing a light from one eye to the other, illuminating the bad eye will lead to paradoxical dilatation on both sides (normally, they stay constricted).

Image result for relative afferent pupillary defect

Don’t believe me, watch this:

The answer to the question, “what makes the symptoms worse” is TEMPERATURE. This is otherwise known as Uhthoff’s phenomenon. High temperature makes many symptoms in this condition worse.

And here he is, in all his glory.

Image result for Uhthoff's phenomenon
Wilhelm Uhthoff describes transient worsening of vision in patients with optic neuritis after exercise in 1890.

In this scenario, patients will typically describe pain at the back of the eye, particularly when moving it, coupled with a reduction in visual acuity.  Usually, there is a distortion of central vision which, when severe, leads to significant problems with reading and colour vision.  The visual disturbance starts off quite subtly, at least to begin with, and gradually becomes more severe as the days pass.

Fundoscopy may reveal a swollen optic nerve head (papillitis), although in many cases the optic nerve looks normal (retrobulbar neuritis = the patient sees nothing and the doctor sees nothing).  After recovery from optic neuritis, the optic nerve head can look rather pale.  We refer to this as “optic atrophy”.

Image result for optic neuritis

Image result for optic atrophy vs normal

You will no doubt have realised that we are talking about Multiple Sclerosis (MS) here.

For more information go to the MS page, or the MS lecture.

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