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2 Ophthalmic Lens

Material and Design

Ophthalmic lens materials means all materials used during manufacturing,
i.e. all materials entered into the composition of the basic ophthalmic lens.
The end result is the specific lens geometry with specific topographical
features, giving the lens its corrective function – what is referred to as lens
design or form. All the ophthalmic lenses currently available in the
ophthalmic industry are:
• Glass material
• Resin material

GLASS MATERIAL

When we consider raw glasses for spectacle lenses, we talk about a material
which has been given a specific composition, shape and size for meeting
its final application, i.e. refracting the rays of light and thereby improving
the eyesight. Raw glasses for spectacle lenses possess all the necessary
optical features but is not delivered in the form of a ready-to-use lenses. It
is, in fact, a molding blank requiring certain finishing operations.
From an optical point of view, a spectacle lens is a medium aimed at
directing light along a specific course and therefore, must possess specific
optical properties. They are designed for day-to-day use under all
conditions. This demands certain mechanical and chemical properties for
comfort, safety and long lasting usage. Lastly, it calls for special
manufacturing techniques which make allowance not only for the qualities
demanded by spectacle lenses but also for economical production.
The components used for glasses for spectacle lenses are vitrifiable
mixture which is put into the melting tank in the form of extremely pure
raw materials so as to obtain perfect quality glass. The basic components
such as silica and alumina are introduced in the respective forms of iron-
free sand and feldspar.
The alkaline oxides (sodium or potassium) are generally added in the
form of carbonates or nitrates. Lime and magnesia are sometimes replaced