Does blue-violet filtering in contact lenses improve contrast sensitivity?

Abstract

PurposeThe work is aimed at (i) comparing photopic contrast sensitivity (CS) of healthy subjects in an indoor environment with either blue-violet filtering (BVF) or clear contact lenses (CLs) and (ii) investigating a possible dependence of the CS variation on the subjects' intrinsic CS, measured with clear CLs. MethodsOptical transmittance of BVF and clear CLs was measured by a spectrophotometer. Photopic CS was measured monocularly on forty-one subjects (nineteen in the age range 20–36 years and twenty-two in the age range 44–66 years) by a digital optotype system at spatial frequencies from 1.5 to 18 cpd, wearing either clear or BVF CLs. The results are indicated as CSclear and CSBVF, respectively. ResultsTransmittance curves in the visible range of the two CLs are very similar, despite an absorption band in the BVF CL spectrum with the minimum of transmittance at 428 ± 4 nm equal to about 79%. For both CSclear and CSBVF, no significant CS difference was found between younger and older adults. The difference [log(CSBVF) − log(CSclear)] showed a decreasing trend and changed sign from positive to negative as a function of log(CSclear) with correlation Spearman’s Rho coefficients ranging from 0.80 to 0.88 (p < 0.01 at all spatial frequencies). ConclusionIn the choice of a BVF CL, practitioners should take into consideration that it can influence photopic CS, improving it for subjects who have a relatively low CS with clear CLs, and worsening it for subjects who have a relatively high CS with clear CLs. BVF can affect positively the CS by reducing intraocular scattering. However, it can also cause a reduction in light intensity, which contributes to the formation of the retinal image. The positive or negative influence of BVF CLs compared to clear ones on CS is attributed to a balance among these effects.