Question & Answer Forum
Is there "a best" softlens to use for piggybacking the Rose K lens over?
In general, Silicon Hydrogel lenses outperform standard soft hydrogel lenses because of their high rate of oxygen permeability. This becomes very important when you are placing 2 lenses on the eye, as each lens contributes to some degree, as an oxygen barrier to the cornea. Maximum comfort and wearing time is usually maximised by choosing the highest oxygen permeable material for both the rigid and soft lens. The soft lens must also be steep and soft enough to wrap around the cone otherwise it can cause abrasions to the cone apex and discomfort. My current materials of choice are Boston X02 and Menicon Z for the Rose K lens and Acuvue Oasys for the disposable soft lens. In some cases where the cone is very steep causing the soft lens to fit poorly, I will use custom made soft lenses such as Custom Optix 02.
Is there a best soft lens to use for piggybacking?
As all eyes are different there is no single lens design which will suit everyone. Because in this lens system the rigid lens is placed over the soft lens, this "sandwich" of two lenses can result in a barrier to oxygen reaching the cornea, resulting in corneal anoxia which can lead to problems including discomfort and reduced wearing time. Therefore it is imperative for the fitter to use high oxygen permeable lens materials for both rigid Rose K2 lens and the soft disposable lens. Paul Rose's current preference is Boston XO2 and Menicon Z for the Rose K2 lens and a soft silicon hydrogel disposable lens for the carrier. A disposable silicon hydrogel soft lens should always be tried in the first instance because of their very high oxygen transmission. However it is important that this lens has a low stiffness modality so it can drape over the cone. Some silicon hydrogel materials are too stiff and can cause an abrasion to the cornea at the cone apex. It is also important that the soft lens fit is optimal and moves on the eye to enhance tear exchange under the lens. If optimum fit cannot be obtained with a conventional disposable lens, then a custom lens such as Air Optics custom can be ordered. It is absolutely imperative that the Rose K2 lens moves independantly of the soft lens. If the two lenses bind together and move as one, this will result in significantly reduced wearing time. In many cases trialling several different silicon hydrogel soft lenses is the only way to find out which design will give the best result.
I find night driving very difficult. Can anything be done to help this?
The majority of keratoconus patients report difficulty driving at night, because of glare and flare particularly from oncoming cars headlights and many try and avoid night driving if they have an option, particularly those patients that have advanced keratoconus. This problem is very difficult for the fitter to overcome completely, however in some cases, going to a larger lens diameter (Rose K2 IC) which has a larger optic zone (seeing area), or changing to a lens design such as Rose K2 which has abberation optics incorporated, or fitting the lens flatter than normal can improve the patients night vision. These problems are produced by either the lens or the cornea as the light passes through these media to the back of the eye (retina), whereby a single focal point onto the retina is not produced, so that you have mutliple focal points which cause ghosting, flare and glare. Because the pupil of the eye gets bigger at night, it is essential (if possible) to make sure that the lens has a large enough optic area so that the patient is not looking through the edge or outside of the optic zone of the lens, as this will always cause poorer vision.