Light adjustable lenses provide tailor-made refraction

March 1, 2009

Pablo Artal discusses the use of light-adjustable lenses to increase the predictability of postop refractive outcomes.

Key Points

It is the combination of residual defocus and astigmatism that accounts for retinal image degradation and reduced quality of vision following IOL implantation in the majority of patients. Naturally, residual refractive errors can be corrected with spectacles, contact lenses or laser refractive surgery; it would, however, be preferable and more elegant to offer an advanced approach to cataract surgery that produces near perfect refraction in a single procedure.

Light adjustable IOLs: a quick introduction

The lenses have four main components: a silicone matrix polymer, a photoreactive macromer, a photoinitiator, and a UV absorbent layer at the back of the lens. Irradiation of the lens through a defined spatial profile polymerizes the macromer in the exposed region: the subsequent diffusion of un-reacted macromer to re-establish equilibrium throughout the lens produces a change in the shape of the lens and therefore a modification of the IOL power. For example, if the lens power needs to be increased, the central part is irradiated to cause the macromer in that area to polymerize. Then time is allowed for free macromer to diffuse down the resulting concentration gradient. The central zone bulges, the radius of curvature decreases, and the focal length decreases. Irradiating on the periphery causes macromer to leave the central zone, producing a flattening of the lens and increasing its focal length. Once the desired refraction (shape) is reached, the entire lens may be irradiated to polymerize all the macromer, making the state of the lens permanent. After this, the LAL may be exposed to UV light (for example, sunlight) and will remain unaltered.

Once the desired refraction is achieved, two additional photo-locking treatments need to be performed, to insure that the LAL is fixed and remains stable. From this point, the LAL behaves entirely as a conventional IOL. The irradiation of the LAL is performed using a custom digital light delivery device that is easy for trained ophthalmologists to operate, and the procedure is quick and comfortable for patients.