Despite what the shop said, your optical mouse does need cleaning from time to time. If it isn’t cleaned, your mouse will get dust in its sensors in a way not dissimilar to how ball mice get dust stuck around their rollers. However, it’s not exactly the same, and when things go wrong, you’ll know it - if your cursor starts jumping around the screen at random, then there’s probably dust in your mouse.
(The next bit involves boring technical explanations of how optical mice work, so those with an allergy to science lessons are advised to skip to the how-to at the bottom of this post.)
Put simply, an optical mouse sends a beam of light down to the tracking surface, and then a sensor detects where the beam has been reflected. It then does some complicated stuff that you probably don’t care about to work out where the mouse is and how much it’s moved. It does this hundreds of times a second.
If there is something in the way of the beam (like a fleck of dust or other debris) then the beam will reflect off that, therefore making the sensor think the tracking surface is in a wildly different place. This can make the mouse cursor jump around the screen seemingly at random.
</boring stuff>
The upside is that optical mice are equally as easy (if not easier) to clean than ball mice. All you’ll need is a cotton bud that would normally be used to clean out your ears (preferably unused).
Now turn the mouse upside down. The light beam does illuminate the dust particles and debris so it shows up quite clearly.
To clean the mouse, simply use the cotton bud to brush away the debris on the underside of the mouse.
(sorry about the poor quality of this image)
Just brush it away gently (don’t poke the cotton bud too far into the mouse or you’ll break the sensor and have to pay for a new mouse - electronics shopkeepers’ joy, but a minor inconvenience to the mouse-owner).
