The lens has an aspherical surface having a zone for far vision, a zone for near vision, and between these two zones, a zone for intermediate vision, with a meridian curve along which the curvature of the surface varies progressively and which is inclined from top to bottom towards the nose side of the...http://www.google.com.au/patents/US5270745?utm_source=gb-gplus-sharePatent US5270745 - Progressive multifocal ophthalmic lens
