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

Purpose: The 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.

Methods: Optical 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 CS_clear and CS_BVF, respectively.

Results: Transmittance 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 CS_clear and CS_BVF, no significant CS difference was found between younger and older adults. The difference [log(CS_BVF) - log(CS_clear)] showed a decreasing trend and changed sign from positive to negative as a function of log(CS_clear) with correlation Spearman's Rho coefficients ranging from 0.80 to 0.88 (p < 0.01 at all spatial frequencies).

Conclusion: In 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.