Mindblown: a blog about philosophy.

The original plastic corneal lens, approximately 11 mm. in diameter and fitted flatter than the optic cap of the cornea.  

A bifocal corneal lens, either one-piece or fused, having both a lower truncation and prism ballast.  

A corneal contact lens whose upper or lower portion (or both) has been removed, resulting in an upside-down or right side-up “D” shaped lens, or in the latter case in a ribbon-shaped lens.  

A corneal lens having an optical zone usually parallel to the optic cap of the cornea, a secondary curve a given number of millimeters (or diopters) flatter than the base curve, and a narrow peripheral.  

Zone demarking the boundary between any two zones on the back surface of a corneal lens (e.g., between the optical zone and the zone of the secondary curve).  

A preservative used in contact lens solutions. A mercury compound used to preserve pharmacological agents and vaccines. An organic mercurial antiseptic used topically and as a preservative in pharmaceutical preparations. Ethylmercury, a crystalline organic compound of mercury, finds application as an antifungal and antibacterial agent. It is present in minuscule quantities within certain vaccines.  

A back surface curve of a contact lens which is just peripheral to the secondary curve and is a certain number of millimeters (or diopters) flatter than the secondary curve.  

A contact lens-telescopic system consisting of a contact lens (ocular) having its negative power confined to a small (2.5 mm.-5.0 mm.) central portion and a .spectacle lens (objective) having its positive power confined to a 10 nun. central portion.