Some manufacture lenses for other optical instruments, such as telescopes and binoculars. Prescription lenses are curved in such a way that light is correctly focused onto the retina of the patient's eye, improving vision. Ophthalmic laboratory technicians cut, grind, edge, and finish lenses according to specifications provided by dispensing opticians, optometrists, or ophthalmologists, and then assemble the lenses with frames to produce finished glasses. Ophthalmic laboratory technicians should not be confused with workers in other vision care occupations. Ophthalmologists and optometrists are eye doctors who examine eyes, diagnose and treat vision problems, and prescribe corrective lenses.
Ophthalmologists also perform eye surgery.
Dispensing opticians, who may also do work described here, help patients select frames and lenses, and adjust finished eyeglasses. Ophthalmic laboratory technicians read prescription specifications, then select standard glass or plastic lens blanks and mark them to indicate where the curves specified on the prescription should be ground. They place the lens into the lens grinder, set the dials for the prescribed curvature, and start the machine. After a minute or so, the lens is ready to be finished by a process in which a machine rotates the lens against a fine abrasive to grind the lens and smooth out rough edges. The lens is then placed in a polishing machine, with an even finer abrasive, to polish the lens to a smooth, bright finish.