All you need is a Q-TIP with some 90% isopropyl alcohol.
Basically the light diode that is used for reading CD's DVD's should look like a little glass "eye". Usually found near the middle of the tray if it indeed is a tray (where the DVD goes). It is usually mounted a moving platform (with usually a ribbon) to read the CD/DVD.
Check this out:
http/37prime.com/bluray_03.jpg
That may be a blu ray/DVD diode combo - but hers should look very similar, albeit, with only 1 eye.
Now make sure the computer is off when doing this and make sure the DVD tray is ejected (also take out the battery on the laptop). You will need much care for this part as to not break anything.
When cleaning the diode - make sure the Q TIP is not moist. It should be slightly damp - and not dripping. All you have to do is wipe the diode gently (and kind of make a turning motion - one way only over the glass eye diode).
Depending on if shes a smoker or not - you may see brown grime on the QTIP. promptly throw away qtip.