Why does the torch the optician uses make a clicking noise?
Answer:
The torch is part of an instrument called an ophthalmoscope (sometimes called a fundoscope).
The ophthalmoscope has two parts; the light to illuminate the inside of the eye and lenses to focus the image for the optician.
The clicking you can hear is the optician changing the lens so that they can see the inside of your eye at a different magnification.