Tuesday, July 15, 2008

The Optician and Active Prisms

Usually, Optician Schools are not able to train opticians in setting active prisms. It requires a very specialised know-how and understanding. This kind of glasses must respect oculomotricity rules to be effective. Opticians are usually trained to set passive prisms. The shape of the frame and the method for centering lenses must follow specific rules. The optician is part of the therapeutical team and he/she must be integrated as a working element. Otherwise, the entire work is at risk. Since we are providing the brain with new information, this information must be highly precise. Multifocal lenses represent a hard task for opticians. Setting the prescribed prisms in the correct place, respecting oculomotrocity rules and choosing the correct frame requires deep knowledge and special training.

Usual optical lenses only have one main task. It consists of putting a focused image on the retina. Active prisms have a different main task. It is to inform the brain. The technical parameters to be respected are different even from passive prisms.

This kind of active prisms needs a frame with a minimum of deepness. For small children, the minimum is 29 mm deep; for other people 30 mm deep; and for multifocals, no less than 32 mm.

The frame must be curved and tilted in order to respect the physiology of eye movements. Both temporal fields must be symmetrical, which means the centering rules must be different from the usual. The orbital asymmetry must be taken into consideration. This means new rules for frame adjustment.

In conclusion, only a specif training for opticians can guarantee good results. Standard opticians do not possess enough knowledge to prepare glasses with active prismes. They can do it, but the results will not be good because they will be missing the correct rules.

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