Evidence weak for blue light-filtering IOLs
A standard IOL now absorbs wavelengths up to 420 nm. Blue light-filtering IOLs block wavelengths between 400 and 500 nm. They are subdivided into blue-blockers, which absorb visible light in the 450-500 nm range and violet-blockers, that absorb visible light in the 410-440 nm range.
Li and colleagues could not find any studies on violet-blocking IOLs. They found 21 studies reporting on outcomes following implantation of blue-light-filtering IOLs. The studies involved a total of 8,914 patients and 12,919 study eyes undergoing cataract surgery.
The researchers classified 7 of these as individual cohort studies or low-quality randomized controlled trials. There were no systematic reviews of cohort studies or individual randomized-controlled trials with narrow confidence intervals.
Of these 7 best studies, only one found better vision with blue-light-filtering IOLs than UV-only filtering IOLs. In this study, researchers randomly selected 30 eyes for implantation with UV-only light filtering IOLs and 30 for implantation with blue-light filtering IOLs. There were no differences in visual acuity or colour vision up to 6 months after surgery, but the blue-light filtered eyes scored better in contrast sensitivity at select frequencies.
This study did not measure or report contrast sensitivity preoperatively in either group, so Li et. al. reasoned the finding may simply reflect better preoperative contrast sensitivity in the eyes scheduled to be implanted with the blue-light-filtering IOL.
In another study, patients implanted with standard IOLs that block UV light only wore either clip-on blue light-filtering spectacles of clip-on UV-only filtering spectacles. The researchers found that the blue-light filtering spectacles increased the patient’s ability to tolerate glare and enhanced their recovery following photostress under conditions of intense light. It is hard to determine how well the results of this experiment applies to actual blue light-filtering IOLs, Li and colleagues noted.
On the other hand, a comparison of another IOL (AcrySof Natural IOL, Alcon), which filters blue light, to single-piece IOLs (single-piece AcrySof IOL, Alcon), which filter only UV light, showed no difference between them in visual acuity, contrast sensitivity, or colour perception among the 93 patients implanted with one or the other.
Likewise, researchers implanted each of 30 patients with UV-only filtering lenses (AcrySof SA60AT lenses, Alcon) in one eye and blue light-filtering lenses (AcrySof SN60WF, Alcon) in the other eye. Two years later they found no differences in visual acuity, colour vision, contrast sensitivity, macular thickness, or macular volume.
Some researchers have tested the influence of blue-light filtering IOLs on night vision, which depends on blue light. In one study, 22 patients with bilateral pseudophakia and early age-related macular degeneration were less able to sort blue socks from navy socks while wearing blue light-filtering spectacles than without the spectacles in dim conditions.