Take it you've never upgraded the 10mm Pistol then?
The 10mm is a Laser sight, which is a cool effect btw.
An optical sight would look like a small frame with a window and a red optical dot in the center:
http://www.jprifles.com/photos_new/JPOINT2C2_500.jpg
So basically it would be similar to aiming down an iron sight, except the aim is "zeroed" at the optical dot instead of the groove.