In the last 10 years or so, the optical profession has seen a colossal transformation in spectacle lens dispensing and in the vast variety of lenses that are commercially available. Some of us will remember when there was no need to question the V-value of an ophthalmic lens material since we really had little or no choice in what we were dispensing. Today, the practitioner has an immense selection of lenses and materials to choose from. It is therefore vital that the practitioner is clear about the optical and mechanical properties of available materials. Choice consequently means awareness, understanding and responsibility. As professionals we have a duty to advise our patients of the advantages and disadvantages of products. The choice of lens material is often one of the first factors to be considered when dispensing a new prescription. To do this effectively the practitioner must have a clear understanding of the properties of ophthalmic lens materials and be able to communicate these facts to the patient. High-refractive-index materials are of course used with the aim of improving the cosmetic appeal of spectacle lenses, particularly in the correction of myopia. The optical performance of the lenses must not however be forgotten. A change in the refractive index does affect the off-axis performance of a lens and, in general, lenses of the same form are not interchangeable when the refractive index is varied.