Patients that undergo cataract surgery often have to wear prescription glasses after the procedure to see properly but a new technology may eliminate this problem.
Based on technology developed by researchers from the University of California, San Francisco (UCSF) and Caltech, Calhoun Vision, Inc. is developing a photosensitive silicone intraocular lens. This lens can be adjusted – non-invasively, weeks after surgery – with a low-power source of light to eliminate refractive errors post implantation.
Currently, patients are said to experience refractive errors after cataract surgery because of unpredictable wound healing, inaccuracies in pre-operative measurements of ocular dimensions, or pre-existing corneal disorders such as astigmatism.
‘With this technology, we can make power adjustments after the lens is in place, wound healing has occurred, and the eye is stabilised,’ said Daniel Schwartz, MD, UCSF associate professor of ophthalmology, director of the UCSF retina division and a co-inventor of the Light Adjustable Lens (LAL).
‘As currently envisioned, the procedure will be relatively simple. The surgeon would implant the LAL using standard surgical techniques. When the eye has healed after two to four weeks, the patient returns to have the lens customised. By directing a cool, low intensity beam of light onto the lens, the surgeon would precisely adjust the lens power to the patient’s specific needs. The lens material is photosensitive and designed to respond in a predictable manner according to the duration and intensity of light delivered,’ said Schwartz.
Initial human trials are expected to begin in the summer of 2002. US clinical trials will follow only with FDA approval. It is anticipated that the lens will be available commercially in Europe in late 2003 and in the United States by 2006.
The in vivo fine-tuning is reportedly based on the interaction of light and photosensitive materials (macromers) that reside throughout the lens. If the implanted lens is under-powered, the physician directs the beam of light to the centre of the lens. This causes the macromers in the irradiated area to bind together to form a polymer.
The unreacted macromers in the non-irradiated area then move toward the centre to equalise their concentration throughout the lens. This physical movement of material is said to cause a swelling in the irradiated area – and an increase in lens power. The physician locks in the optimised LAL power by treating the entire lens with light, thereby consuming all remaining macromers.
For the opposite effect – a reduction in lens power – the physician would treat the periphery of the lens instead, driving unreacted macromers to that area.
The treatment of astigmatism, a commonly occurring irregularity of the cornea that causes blurred vision, could be accomplished in a similar fashion, by suitably orienting the light beam.
The researchers note that this technology may have application beyond correcting vision problems in post cataract surgery patients. The lens could potentially be used as an alternative to Laser-Assisted In Situ Keratomileusis (LASIK) surgery for severe myopia, said Schwartz.
He explained that LASIK surgery for severe myopia has resulted in complications including glare, halos and unpredictable refractive outcomes.
LALs may also be effective in treating farsightedness, which often cannot be treated optimally with LASIK surgery. The ability to implant and precisely adjust lens power post-operatively offers farsighted patients a wider range of correction and potentially more predictable outcomes than LASIK.