The fitting of keratoconus has steadily evolved since the 1950’s and in particular during the last 15 years.
MICRO CORNEAL DESIGN AND PIGGY BACK APPROACH:
During the decades of the 50’s, 60’s and 70’s, the primary design used was micro corneal contact lenses. They ranged between approximately 8 to 9.7 mm in diameter and were fit with the intention to have a mild central touch and then landing on the cornea at the outer edge. It was called a three point touch. One of the primary downsides of this approach was the central bearing of the contact lens which would over time, lead to progressive central corneal scarring. This was mitigated by the introduction of the ‘piggy back’ method. In this case, a thin soft contact lens with little or no prescription was applied to the eye first and then the micro corneal lens was put on top of the soft lens.
This went a long way to reduce the formation of scarring and on a symptomatic level; it appreciably reduced contact lens awareness and the occurrence of dust and grit getting between the lens and the cornea.
SOFT CONTACT LENS DESIGNS:
There are several soft lens designs specifically manufactured for keratoconus. These are only suitable for mild to mild plus cases of keratoconus and present less than optimal visual acuity in most cases. Despite these short comings, they do have a place in my practice.
During the late 80’s and well into present day fitting, a new design was developed which combined the soft and rigid lens, giving birth to the ‘hybrid’ design. It is literally a 2 part lens with a rigid centre fused to a soft skirt. The design is still very much in use today and is constantly evolving. Unfortunately, this design still presents corneal bearing albeit peripheral to the central corneal cap.
SCLERAL LENS DESIGN:
Although this design was in use during the 50’s and 60’s, the method of manufacture was all but entirely made by hand beginning with a plaster cast made of the external adnexa (cornea and surrounding scleral tissue). My father and eldest brother (Fred and John Sanger respectively) utilized this method in many cases.
During the 1980’s, these lenses were being made with lathes to approximate the corneal topography. Unfortunately, there were many drawbacks to this method and the equipment for manufacture had many limitations. As the decades went by, computer assisted lathing dramatically altered scleral design and manufacture.
Today, the designs and control of the end product is all but limitless and has resulted in spectacular results and predictability.
Scleral contact lenses are fit without any corneal touch, leaving a saline filled vault of approximately 200 microns between the back of the lens and the cornea. The lens is fit to land on the sclera only.
This method has resulted in an extremely comfortable lens, exceptional visual acuity and without corneal insult. It is without a doubt (in almost all cases) the best method to utilize.