Rigid contact lenses – the new terminology
Rigid contact lenses are available in many forms. In the past, the classification of rigid lenses was based on differences in total diameter, although the terminology was variable. I tended to favour the classification system whereby corneal lenses had a diameter of 7.0 to 12.0 mm, corneo-scleral lenses had a diameter of 12.0 to 15.0 mm, mini-scleral lenses had a diameter of 15.0 to 18.0 mm and scleral lenses had a diameter of 18.0 to 25.0 mm. In addition – as outlined in an earlier blog – the term ‘rigid lenses’ now refers to all lenses made from rigid gas-permeable materials; the term ‘rigid gas permeable lens’ is no longer necessary and hence should not be used.
With the dramatic increase in the usage of the larger diameter rigid lenses – especially what we presently refer to as the mini-scleral lenses – the Scleral Lens Education Society has moved away from a diameter-based classification for rigid lenses. They now define the type of rigid lens based on where it is bearing (or resting) on the eye. Hence, corneal lenses only show bearing on the cornea, rigid lenses resting partly on the cornea and partly on the sclera are known as corneo-scleral lenses, and scleral lenses only show bearing on the sclera.
Note that the new terminology to define scleral lenses removes the distinction between ‘mini-scleral’ and ‘scleral’ lenses. All scleral lenses, regardless of size, are fitted to completely vault over the entire cornea (including the limbus) and land on the conjunctiva overlying the sclera, thus there is no need for distinction and the terminology can be simplified to ‘scleral lenses’ for all sizes. The term scleral is appropriate on the basis of naming the lens by where it distributes its weight or bears on the ocular surface.