The authors report the result of a retrospective registry-based cohort study of 11028 cataract surgeries (11028 patients) performed over a 11-year period of time (2007-2018) in a single Finnish center. The authors compared the onset and the progression of glaucoma during the follow-up in two parallel groups of intraocular lenses (IOL), the first group received a blue-light filtering IOL (SN60WF, Alcon inc.) (n = 5188 eyes, 47%) and the second group received a non-blue-light filtering IOL (ZA9003 or ZCB00, Johnson & Johnson inc.) (n = 5840 eyes, 53%). During the follow-up, 316 eyes developed glaucoma and 662 eyes were already followed for glaucoma. A cox regression survival analysis was performed and showed after adjustment for age and gender, a 22.2% lower risk of glaucoma onset for the blue-light filtering IOL group (Hazard ratio (HR): 0.778 95% Confidence Interval (CI):0.621- 0.975, P = 0.029), whilst eyes with a diagnosis of glaucoma had a 38.4% lower risk to have a glaucoma procedure during the follow-up again in the blue-light filtering IOL group (HR: 0.616,95%CI:0.406-0.935, P = 0.023). Interestingly, the magnitude of differences between the two groups gradually increased during the follow-up.
Due to its short wavelength, blue-light is not absorbed by the cornea and is supposed to be harmful on the retina pigment epithelium and could be associated with the onset of age-related macular disease. Some experimental studies suggested that blue-light could also be harmful on retinal ganglion cells. Indeed, due to their non-myelinated characteristics, retinal ganglion cell axons have a large mitochondrial activity to enable the transmission of nerve impulses. Some studies showed that short wavelength light (400-460 nm) could be absorbed by the mitochondrial chromophores and could thus impair mitochondrial function.
While the study is likely well-powered with a large sample size and a long duration of follow-up in the two groups, its retrospective design could be associated with a significant risk of attrition bias that could limit the generalisability of the authors' findings. Noteworthy, despite intraocular pressure is known to be the main risk factor for glaucoma onset and progression, the authors did not include this parameter in the multivariate analysis. Thus, a potentially significant confounding factor was not taken into account in the survival analysis that could bias the estimate of the exposure of retinal ganglion cells to short wavelength light.
In conclusion, while cataract surgery is a common procedure, the influence of blue-light on the onset and progression of glaucoma would need to be further analyzed in a prospective randomized clinical trial to enable strong recommendation for IOL implantation.