A possible strategy for implanting blue‐blocking intraocular lenses

Abstract

Editor, Age-related macular degeneration (AMD) is said to be associated with sunlight exposure. This is supported by some epidemiological studies but not others. Epidemiological studies have also shown AMD progression following cataract surgery (Cuthbertson et al. 2009). Lipofuscin is considered a biomarker for cellular ageing and oxidative damage with one fluorophore A2E found in the retinal pigment epithelium (RPE) with peak sensitivity of short wavelength. It is thought to be an important mediator of AMD progression generating reactive oxygen species on photoexcitation and being phototoxic to RPE cells in culture (Algvere et al. 2006). Short wavelength light is absorbed by the ageing crystalline lens and this protective effect is lost following cataract surgery, likely resulting in cellular damage as a result (Algvere et al. 2006). Experimental studies showing the protective nature of a yellow intraocular lens (IOL) against radiation damage between 400 and 500 nm and the peak blue-light hazard of wavelengths at 435–440 nm (ICNIRP 1997) support this hypothesis (Cuthbertson et al. 2009). However the data is experimental and with conflicting evidence from epidemiological studies, the role of sunlight exposure in AMD remains inconclusive. In the 1980s, patients undergoing phacoemulsification surgery were given protection against radiation of wavelengths below 400 nm with clear UVR-blocking IOLs but not the blue-light hazard. Considering the experimental (Ham et al. 1976) and the epidemiological evidence that blue light induces damage in the retina, it is rational to implant a yellow IOL following phacoemulsification surgery, in patients at risk of AMD. However, early theoretical reports suggest yellow IOLs may have an effect on scotopic vision, reducing visual performance and contrast sensitivity when compared to a clear IOL due to blue light absorption. On the other hand, filtering out blue light improves the contrast on the retina in the sense that Rayleigh scattering in the vitreous is inversely proportional to the forth power of the wavelength. With foveal scotopic vision decreasing with age, the loss of blue light in the image caused by yellow IOLs may have an impact on night activities such as walking down stairs. Theoretical comparison between yellow IOLs and a middle aged crystalline lens indicated that the loss of blue light in the image may cause reduced scotopic sensitivity but this may not be clinically significant for scotopic vision and clinical trials with blue blocking IOLs have demonstrated no impact on contrast sensitivity (Cuthbertson et al. 2009). Blue light is said to have a role in the regulation of circadian rhythms which could affect sleep and lead to depression, although it is unclear how clinically relevant this is. Therefore, using clear IOLs with UV filters is also recommended over yellow IOLs further complicating the choice in IOL selection. Ideally, an IOL should have no effect on scotopic sensitivity and circadian rhythm with maximal protective effective against short wavelength phototoxicity. However, each of these scenarios has different peak wavelengths and therefore IOL selection will be a balance of these functions. Thus, clinical trials were not able to demonstrate a negative impact of blue blocking IOLs (Cuthbertson et al. 2009). However, if concern exists one option is to implant a clear IOL in one eye and a yellow IOL in the fellow eye. In a patient with bilateral asymmetrical AMD, we recommend that consideration should be given to implanting the yellow IOL in the eye with less severe disease to minimize AMD progression. The literature reports that most patients do not notice a problem with colour vision having a clear IOL in one eye and a yellow one in the other (Marshall et al. 2005; Algvere et al. 2006). There is only one case report of a patient who required explantation of the yellow IOL due to colour perception problems (Shah & Miller 2005). We anticipate this strategy will help minimize AMD progression and while preserving scotopic vision for patients undergoing cataract surgery if scotopic vision is an issue.