CE marked in April of 2006, the KS-3Ai has become the first preloaded aspheric silicone IOL to be approved in Europe for use in cataract surgery. Although the product has yet to gain approval in the US market, it is already available in Japan and will shortly be entering clinics in Europe.
So what is it that makes this lens so different? And how much of an improvement is this over existing models? To try and answer these questions, we have enlisted the help of one of our Japanese colleagues who has played a significant role in the development of the product. Here, Kimiya Shimizu, MD explains why he regards KS-3Ai as a significant advance in the field of cataract surgery.
A Japanese account
In my opinion, in order to perform cataract surgery and to ensure a good outcome, several prerequisites must be met; surgeons must be able to make a small, temporal corneal incision to reduce the incidence of iatrogenic induced astigmatism, phacoemulsification and aspiration (PEA) must be safe and efficient and one must have several foldable IOLs available so that each patient is catered for adequately.
Although we have recently witnessed an introduction of equipment that can be used through a 2.2 mm sclerocorneal incision with co-axial surgery, I do feel that uptake of this equipment will be fairly slow, simply because many may find the new technique associated with use of the equipment a little difficult to master.
KS-3Ai is the first aspheric foldable IOL to be introduced to the Japanese market. The injector is a further development of the KS-1 and KS-3 series that have been available on the international market through STAAR Surgical for more than three years. The IOL is already loaded in the disposable injector and provides a sterile pathway directly to the eye, resulting in a consistent, controlled and safe delivery. The plunger pushing the IOL forward in the injector serves as a positioning instrument for the trailing haptic into the capsular bag and no additional manipulator is necessary for introduction into the eye.
A review of the literature
Various clinical studies have been conducted on this aspheric IOL comparing it with conventional spherical IOLs. I would cite Contrast Sensitivity of Eyes with Aspheric IOL under Lower Illuminance reported by Miyata, Oshika, et al. as the most significant of these studies. In this study, KS-3Ai was implanted in one eye and KS-3 (CanonSTAAR, Japan) with 6 mm spherical IOL as a control in the fellow eye of 40 patients (14 male and 26 female; mean age 69.8 ± 5.0 years) who had no more than 1D of corneal astigmatism and did not have any ophthalmic disorders other than cataract.
The most significant observation made in this study was in those eyes implanted with aspheric IOLs. These eyes showed significantly less spherical-like aberration and all higher order aberration in wavefront aberrations (all refractive components) compared with eyes implanted with spherical IOLs at six months postoperatively.
Furthermore, when the contrast sensitivity was compared under normal bright illuminance (around 200 lux) and under lower illuminance of supposed twilight (around 50 lux), eyes implanted with KS-3Ai aspheric IOL showed significantly better results at spatial frequencies of 3, 6 and 12 cyl/deg under 50 lux, even though there was no significant differences under bright illuminance. This is very interesting as the results strongly suggest the possibility of greater improvements in visual function in twilight as a result of the aspheric IOL correcting spherical aberration compared with those eyes implanted with conventional spherical IOLs.