PROGRESS IN LENS DESIGN

Advances in the design of contact lenses are reducing the need for corneal grafts in keratoconus patients, according to Ebru Toker MD, Marmara University Medical School, Istanbul, Turkey.
“The contact lens management of keratoconus is challenging and it demands greater expertise compared to standard contact lens fitting. But we are lucky to have many designs and materials for our patients, and with the appropriate selection and application of these lenses, we can restore vision in most of these patients without the need for surgery,” Dr Toker told the 19th ESCRS Winter Meeting in Istanbul.
Rigid gas permeable lenses provide excellent vision to patients with mild forms of keratoconus. They rest on the cornea and are fitted in alignment with the cornea. Because of their rigidity they provide optimal centration and mask corneal irregularities. However, as the cone advances, a conventional rigid gas-permeable lens will become unstable with frequent dislodgement, resulting in epithelial disruption and progressive scarring of the cornea.
But there remain several contact lens options for even the more advanced cases. For example, there are specialty RGP contact lenses with complex designs that can be selected based to the shape and the position of the cone. 
In addition, for patients in whom rigid gas-permeable lenses cause discomfort there are now custom piggyback lens systems, consisting of a soft lens with a circular recessed depression in the centre within which is fitted the rigid lens. 
There are also new soft lens designs with a thick central optical zone that mimic the behaviour of a rigid lens and can therefore mask some mild to moderate corneal irregular astigmatism.

BONDED
For patients with advanced keratoconus or in cases where the other lenses don’t work, there are also hybrid lenses consisting of a rigid RGP centre with apical clearance that is covalently bonded with a hydrogel skirt that extends from the limbus out to the sclera. 
Finally, for really hard-to-fit eyes, there are the new scleral lenses. With diameters ranging from 15mm to 24mm, the lenses are supported exclusively by the sclera and completely avoid the cornea and the limbus. They are therefore much more comfortable than a rigid corneal lens. 
Dr Toker cited a retrospective study showing that, in eyes with stage 4 keratoconus, those implanted with the new lenses had significantly better visual acuity than those who underwent keratoplasty.
“It seems that these new scleral lenses with sophisticated designs will reduce the need for keratoplasty for advanced keratoconus,” she added.

Ebru Toker: dretoker@gmail.com