MAR 17, 2009
Researchers implanted 14 patients (14 eyes) with light adjustable lenses that would purposely result in hyperopic refractive errors up to +2.0 D. After surgery, they adjusted lens power with a digital light device.
More than 90 percent of patients were corrected to within 0.25 D of the intended refraction. Uncorrected visual acuity improved in 64 percent of patients while BCVA was maintained after "lock-in" in all patients. The uncorrected and best-corrected visual acuity was stable for all patients at final follow-up, up to six months. All eyes were stable within ± 0.25 D, with 13 eyes showing no change at one to six months follow-up.
The light adjustable lens contains photosensitive silicone molecules that enable postoperative, noninvasive adjustment of refractive power using ultraviolet (UV) light. The light adjustable IOL formulation is based upon the principles of photochemistry and diffusion. The application of the appropriate wavelength of light through a defined spatial irradiance profile onto the light adjustable lens polymerizes macromer in the exposed region producing a change in shape and associated predictable power change. By controlling the irradiation dose (i.e., beam intensity and duration) and spatial irradiance profile, the refractive power of the light adjustable lens is modified to add or subtract spherical power, eliminate astigmatic error, and correct higher-order aberrations. For example, to correct hyperopia, irradiation is preferentially applied to the center of the lens. This causes photopolymerization and subsequent diffusion of unpolymerized macromer into the irradiated zone. Subsequent swelling of the irradiated zone increases lens power to correct hyperopia. To control the amount of hyperopia corrected, the treatment duration is varied. One day after light adjustable lens adjustment, the entire lens is irradiated to polymerize the remaining photosensitive macromer and prevent additional change in lens power. This second irradiation procedure is referred to as "lock-in." In vitro studies have achieved a +3.5 D power change with secondary adjustments of light adjustable lenses.
The authors note that while this was a feasibility study and adjustments were performed in patients who had not had previous refractive surgery, they say it is likely that correction of hyperopia could also be performed in a similar fashion in patients who have had refractive surgery.
An important aspect of the light adjustable lens is the need to wear UV protective spectacles until lock-in is performed. This is because the photoreactive silicone macromer undergoes photopolymerization when exposed to UV light. The light adjustable lens has approximately one hour of built in UV protection in the absence of sunglasses, but after that there is a risk for photopolymerization and optical changes. Therefore, patients are instructed to wear the UV blocking sunglasses until lock-in is completed. After lock-in, no UV protection is necessary.