Revised British spectacle lens standards

The latest editions of BS EN ISO 10322, Ophthalmic optics – Semi-finished spectacle lens blanks – Part 1: specifications for single-vision and multifocal lens blanks and –Part 2: specifications for progressive-power and degressive-power lens blanks have just been published. They will be of interest to prescription houses and practices with their own surfacing laboratory.

With the increase in free-form surfacing, progressive-power lenses are now mostly produced using single-vision semi-finished lens blanks. Hence lens blanks (the abbreviation used throughout the standards) are now classified by the form of the finished surface, not the intended use.

The reference method for measuring surface curvature and hence power is now by reflectometry and not measurement of the sag for single-vision and multifocal lenses or calculation from vertex power for progressive-power lens blanks. Both standards now have orientation requirements for polarizing lens blanks. For single-vision lens blanks, the marking is usually along the intended horizontal orientation. Some manufacturers confusingly mark along the vertical, for the sensible reason that such marks, often notches in the edge of the blank, will not encroach on the usable area of the lens since the vertical boxed lens size is always less than the horizontal size. Such vertical marking is to be clearly identified as such.