CD lens cleaners are usually just a regular disc with tiny brushes glued to the readable side of the disc. The brushes then wipe dust from the optical lens while the disc is spinning. In theory, this clears away dust, dirt and other grime, which may build up over time, from the drive's laser lens, resulting in cleaner reading of discs.

On the Other: They Might Not Help and Could Even Harm a Drive

In reality, it seems that the use of lens cleaners may not be as vital to the maintenance of CD drives as commonly perceived. While lens cleaners may be effective in removing minor dust, there is no guarantee that they won't just move that dust around. Really nasty grime, like greasy buildup from tobacco residue or grease, will likely prove too difficult for a lens cleaner to remove. What's more, no industry standard exists for lens cleaners, so a cleaner may do nothing and could even scratch a drive's lens.

Bottom Line

CD lens cleaners may help with minor dust or dirt problems, but a superior quality disc that times the cleaning process (usually no more than 15 seconds) and has higher quality cleaning bristles is still recommended. Still, since there is no standard for lens cleaners, there is always a risk that the disc may do no good at all, or worse, it could damage a drive.

Source:

repairfaq.org: CD Lens Cleaning Discs

SearchEnterpriseDesktop.com: CD/DVD Cleaning Discs May Do More Harm Than Good

tnt-audio.com: Allsop CD Laser Lens Cleaner