Improvement or Worsening of Human Contrast Sensitivity Due to Blue Light Attenuation at 450 nm

PURPOSE: The work was aimed at comparing contrast sensitivity performance in an indoor environment with two filters, which differ only in the presence of a band at 450±20 nm in the transmittance spectrum. PATIENTS AND METHODS: Thirty-nine subjects participated. The filters were the Standard (ST) and Professional (PRO) Drive lenses (Hoya, Japan), the latter showing the attenuation band at 450 nm. Photopic contrast sensitivity (CS) was measured at different spatial frequencies from 1.5 to 18 cpd through Functional Acuity Contrast Test with both lenses (LogCS(ST) and LogCS(PRO), respectively). The areas under the curves of LogCS(ST) and LogCS(PRO) as a function of the spatial frequency were also considered. RESULTS: In the range of the measured values of LogCS(ST) for the thirty-nine participants, at each spatial frequency and also for the areas, the difference Δ = LogCS(PRO) – LogCS(ST) was found to decrease and change sign from positive to negative as a function of LogCS(ST), thus allowing to deduce a threshold (LogCS(threshold)) for LogCS(ST) corresponding to Δ=0. Significant CS worsening was found with the PRO compared to the ST lens for the subjects showing LogCS(ST) > LogCS(threshold). Vice versa, CS improvement was found when LogCS(ST) < LogCS(threshold). CONCLUSION: In the choice of a blue-filtering lens, practitioners should take into consideration that the attenuation of light in the range 420–470 nm is expected to produce a CS worsening in subjects showing a relatively high initial CS (higher than a threshold CS). For these subjects, the general reduction of transmitted light intensity prevails on possible advantages. On the contrary, subjects showing a relatively low initial CS are expected to show a CS improvement because the attenuation of light in the range 420–470 nm is expected to reduce intraocular scattering and to mimic the effect as an optical filter of the human macular pigment, advantages which prevail on the reduction of the transmitted light intensity.