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What is the best way to troubleshoot an ophthalmic handheld device that is not working?  Common examples are a direct ophthalmoscope, a muscle light, a retinoscope, or a glare tester.  The light is not working.  What is the first thing you do to get it working again?

A. Replace the bulb with a new one. 
B. Replace the battery with a new one.
C. Put it back in the charger for another few hours.
D. None of the above.

I would argue that the correct answer is none of the above, for the following reasons:

A. The bulb is typically one of the most difficult parts to replace in these instruments, so I prefer to start with the battery.

B. A new battery may not be charged, thus providing you with no help in your troubleshooting.

C. Putting it back in the charger is generally a waste of time.

I find that the fastest way to troubleshoot a battery powered handheld device is to find an identical instrument that is working.  This way you know that you have a working bulb and you have a working battery.  Switch the batteries between the two instruments.  You want to switch both batteries because this will tell you if you have a bad bulb and a bad battery, which sometime happens.  If the non-working instrument does not light with the good battery, you know that there is a problem with the bulb.  If the working instrument does not light with the switched battery, you know that the battery is also dead.  Remember that a dead battery does not necessarily mean that the battery is bad, it may just need to be charged.  If you have many exam rooms, it is possible that you have an instrument stand with a non-working charger.  When charging a dead battery, it is best to use a stand alone charging unit that you know works.