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The following tips are designed to help trainees or inexperienced neurologists to reach the right answer in a time-efficient manner. The tools required are easily carried. The list is personal and idiosyncratic; other experienced neurologists may feel they can improve on it. Some tips are very simple and most trainees will know them already, but experience shows that not all do.
Expert clinicians use the examination to test hypotheses and solve problems: for this to work you need to ‘think on your feet’ and adapt the examination to the circumstances. This includes confirming abnormalities in detail when a screening test is positive. Likewise, any unexpected abnormality on examination must be confirmed, with its relevance being determined in the context of the history and the overall clinical presentation.
COLOUR DESATURATION IS A SIMPLE SCREENING TEST FOR OLD OPTIC NEURITIS
Hold up a red object such as the top of a hatpin and cover each of the patient’s eyes in turn. Ask whether the colour seems washed out or dulled in one eye compared with the other.
Clearly, this detects asymmetrical colour desaturation. Its advantages are that it is quick and reasonably sensitive. It can be included in the examination with minimal loss of time even when the chance of a positive response is quite low. Naturally, a positive response or a history suggesting that optic neuropathy is likely should provoke a more detailed assessment for evidence of optic neuritis.
Other signs of old optic neuritis include the following:
Pale optic discs (subtle changes may be difficult for the inexperienced).
Impaired colour vision when tested formally with Ishihara charts (more time-consuming).
Afferent pupillary defect (quick, effective and well known, but subtle changes may be difficult to see).
Subtle central or paracentral field defects (not easy to detect at the bedside by ordinary methods). Testing visual fields with a laser pointer can be helpful. …
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