It’s time to call a spade a spade: rigid contact lens nomenclature

Rigid contact lenses are available in many forms.  In a previous blog that was published about 5 years ago, I wrote about how the classification of rigid lenses was usually based on differences in lens diameter such that corneal lenses were considered to have a diameter of about 7.0 to 12.0 mm, corneal-scleral lenses a diameter of 12.0 to 15.0 mm, mini-scleral lenses a diameter of 15.0 to 18.0 mm and scleral lenses a diameter of 18.0 to 25.0 mm.  Unfortunately, over the past few years it became obvious that defining the various types of rigid lenses by lens diameter ranges was problematic because more than one of the above terms could be used to describe a lens of given diameter, depending on the corneal diameter of the patient.

 

Earlier this year, I was one of the authors of an editorial published in the esteemed Australian journal Clinical and Experimental Optometry.  The title of the paper was the same as the title of this blog and my fellow authors were world renowned contact lens experts Professor Nathan Efron and Associate Professor Stephen Vincent (both from the School of Optometry and Vision Science at the Queensland University of Technology).  The motivation for writing the paper was that Nathan, Stephen and I believed that the terminology used to describe contact lenses – especially rigid contact lenses – had become confusing for two reasons.

 

First, a range of supposedly synonymous terms, abbreviations and acronyms used to describe contact lenses – such as ‘hard lens’, ‘rigid lens’, ‘flexible lens’, ‘rigid gas permeable lens’, ‘RGP lens’ and ‘gas permeable lens’ –had emerged.  In our paper Nathan, Stephen and I state that it is ‘time to call a spade a spade’ and recognize that the three main contact lens types available today should simply just be referred to as soft, rigid and ‘hybrid’ lenses (with hybrid lenses having a rigid central portion and a soft skirt).  Secondly, in regard to the classification of rigid contact lenses, we agree with the recent recommendation by both our North American and UK colleagues that a new ‘tissue bearing-based’ set of definitions would be more appropriate, whereby rigid lenses of different sizes are classified based on whether the lens bears upon the cornea, the scleral (and overlying conjunctiva), or both.  Hence rigid corneal lenses are lenses that only bear on the cornea; rigid corneoscleral lenses bear on both the cornea and sclera (conjunctiva); and rigid scleral lenses bear primarily on the scleral (conjunctiva).