BLOG: Should we prescribe blue-filtering IOLs?

I recently came across an interesting study by Nagai and colleagues looking at implantation of blue-filtering IOLs and the development of age-related macular degeneration changes as measured by fundus autofluorescence.

The study included 52 eyes implanted with a blue-filtering IOL and 79 eyes implanted with a clear (UV blocking) IOL. Outcome was measured based on the International Fundus Autofluorescence Classification Group (Bindewald et al.) Findings were recorded at baseline and 2 years post-op.

The authors found that: “Abnormal fundus autofluorescence (FAF) did not develop or increase in the yellow-tinted IOL group; however, progressive abnormal FAF developed or increased in 12 eyes (15.2%) in the colorless IOL group (P = .0016). New drusen, geographic atrophy and choroidal neovascularization were observed mainly in the colorless IOL group. The incidence of AMD was statistically significantly higher in the colorless IOL group (P = .042).”

The authors concluded: “Two years after cataract surgery, significant differences were seen in the progression of abnormal FAF between the 2 groups. The incidence of AMD was lower in eyes with a yellow-tinted IOL.”

It is hypothesized that cumulative blue light exposure in genetically susceptible individuals is a precursor to the development of AMD. FAF is mainly derived as a result of lipofuscin accumulation in the retinal pigment epithelium (RPE). Lipofuscin is formed by light (including blue light) striking the retina, causing photoreceptor outer segments to be shed and phagocytized by the RPE. Based on one’s genetics, lipofuscin accumulation in the RPE is a precursor to drusen or pigment alterations leading to AMD. In addition, lipofuscin contains the chromophore A2E that is particularly sensitive to blue light exposure, inducing oxidative damage within the RPE cells to mitochondria and DNA.

So, a damaging pattern emerges: blue light leads to accumulation of lipofuscin, which over time leads to the formation of drusen and other RPE alterations. As the lipofuscin contains A2E, which is particularly sensitive to blue light, further cellular damage takes place as the eye is exposed to blue light.

So, according to the results of this study, our patients undergoing cataract surgery should receive a blue filtering IOL, right? Well, maybe...

While the aging human lens is a natural blue light filter, eventually cataracts set in, and removal of the lens becomes necessary. We then need to make a choice for the patient regarding IOL selection: a clear or a blue-filtering IOL. Looking at the results of this study it would seem to be a no-brainer that we should recommend our patients receive a blue-filtering IOL. However, what this study and others like it fail to take into account is the other blue light filter in the eye, the macular pigment.

The macular pigment is made up of the carotenoids lutein, zeaxanthin and mesozeaxanthin. It is located prereceptorally, filtering blue light before it strikes the photoreceptors or RPE (for a review, see my previous blog, “The Cocktail Napkin Talk”). The amount of macular pigment varies widely by individual. However, studies by the Macular Pigment Research Group in Waterford, Ireland, show that supplementing with all three macular carotenoids builds macular pigment levels more efficiently than those that do not.

So, as a precursor to cataract surgery, why not place our patients on a proper carotenoid supplement? Think of macular pigment like sunscreen: You can’t have too much; build it maximally.

Another consideration is that of scotopic vision. There are approximately 90 million rods and 4.5 million cone photoreceptors in the human retina. However, the fovea is devoid of rods, as they are more concentrated in the peripheral retina, peaking at approximately 20 degrees of eccentricity from the fovea. However, rods, which mediate scotopic vision, are most sensitive to blue light. Aging has little effect on the number of foveal cone photoreceptors, but parafoveal rod photoreceptors diminish by 30% (Curcio et al.).

Practicing in a retirement area, a common complaint I hear is that “I need more light,” whether that be for reading in a dim restaurant or driving at night. Do I really want my co-managing surgeon to take out a lens that is blocking light and insert another that blocks the light needed most for vision in dim situations?

This study demonstrates yet another reason as to why it is important to discuss ocular nutrition and, in particular, carotenoid supplementation with our patients. This should be done before the age of cataracts. Maintaining a healthy level of macular pigment throughout one’s lifetime stands to prevent photo-oxidative retinal damage before and after the time of cataract surgery. And of course there are now options for blue-filtering spectacle lenses that we can prescribe to be worn postoperatively in photopic environments, just as we can prescribe non-blue-filtering lenses for use in scotopic environments. Let’s keep the future bright for our patients.

References:

Bindewald A, et al. Invest Ophthalmol Vis Sci. 2005;46:3309-3314.

Curcio CA, et al. Invest Ophthalmol Vis Sci. 1993;34:3278-3296.

Nagai H, et al. J Cataract Refract Surg. 2015;41(9):1855-1859. doi: 10.1016/j.jcrs.2015.01.017.