Medical and surgical instruments and apparatus, in particular surgical instruments and apparatus for eye surgery; optoelectronic apparatus and devices for eye examinations and ophthalmic devices, in particular slit lamps, ultrasonic apparatus, pachymeters and biometers, ophthalmological lasers, optotype projectors, phorometers, retinal lasers and ophthalmoscopes; artificial eyes, in particular intra-ocular artificial implants, intra-ocular lenses for surgical implantation