Within the optical field, there are several specialties. An opthamologist and optometrist are the highest grade of eye technician, doing surgery, removing cataracts, certified to use the excimer laser to cure nearsightedness, etc.
One step below that is the optician, the eye technicians who takes eye tests and fits you for glasses and contact lenses among other things.
Optometrists diagnose, manage, and treat basic conditions and diseases of the human eye. Their practice consists of eye examinations, diagnosis of problems, and the prescription of corrective lenses.
Dispensing opticians fill the prescription that is written by an optometrist. They design, measure, fit and help select frames for their patients.
An ophthalmologist is a physician who diagnoses and treats eye diseases.
For the brain to interpret the information transmitted along the optic nerve, to blend the two separate images into a single image and to be able to judge distances correctly, the two eyes must work together.