Abstract: Apparatus is provided for effecting medical or dental surgery, and to a related method. A subject body on which surgery is to be performed has a reference thereon or therein identified, such as a layer in the cornea, or a surface of a tooth. A handpiece contains a variable focus lens, and a fiberoptic bundle is connected axially to the proximal end of the handpiece to illuminate the site. The image of the site is passed to a control apparatus for adjusting the variable focus lens so as to provide for focussing of the treatment laser beam at a predetermined distance from the reference.A method of performing surgery comprising determining by focus condition measuring equipment the distance of a reference in a subject body, adjusting a variable focus lens by control signals proportional to the focus condition measured, and passing a laser beam through the variable focus lens in the adjusted position. to provide a focus spot of the laser beam at a predetermined distance from the reference.