Estimation of the melatonin suppression index through clear and yellow-tinted intraocular lenses.

PURPOSE: To estimate the melatonin suppression index (MSI), which may reflect the nonvisual photoreception function, through commercially available foldable, clear and yellow-tinted intraocular lenses (IOLs). METHODS: The MSIs for 13 IOL models (6 clear IOLs, 7 yellow-tinted IOLs) with three lens powers were calculated based on previously reported data about the melatonin suppression spectrum, spectral intensity of a 20-W white fluorescent lamp and spectral transmission of IOLs in wavelengths from 300 to 800 nm. The models tested were the SA60AT and SN60AT (Alcon Japan); the VA-60BBR, YA-60BBR, and NM-1 (Hoya); the AU6K and AN6K (Kowa); the N4-18B and N4-18YG (Nidek); the X-60 and NX-60 (Santen); and the KS-3Ai and KS-AiN (Staar Japan). RESULTS: The MSIs of the clear IOLs ranged from 1.12 to 1.18 mW cm(-2) sr(-1) and those of the yellow-tinted IOLs from 0.74 to 1.01 mW cm(-2) sr(-1). All yellow-tinted IOLs had significantly lower MSIs (P < 0.0001-0.0021) than the clear IOLs; the %MSI cutoff values for yellow-tinted IOLs compared to the clear IOLs were 11.4-36.2 %. The MSIs of the six clear IOLs did not differ based on lens powers (P = 0.2159-0.6144). Except for one IOL model, all yellow-tinted IOLs had a lower MSI with higher lens powers compared to those with lower lens powers (P < 0.0001-0.0055). Compared to phakic eyes (MSI, 1.03 mW cm(-2) sr(-1)), the MSIs of the clear IOLs were higher (%MSI cutoff, -14.6 to -8.4 %), whereas those of the yellow-tinted IOLs were lower (2.6-28.1 %). Compared to aphakic eyes (MSI, 1.21 mW cm(-2) sr(-1)), the MSIs of the clear (2.1-7.4 %) and yellow-tinted (16.7-38.6 %) IOLs were lower. CONCLUSIONS: Yellow-tinted IOLs absorb more circadian rhythm-associated light than clear IOLs. The difference in the lens power is significantly related to the MSI value in some yellow-tinted IOLs. To correlate the current data with the clinical relevance of these findings, the percent loss of the MSI leading to a circadian rhythm disorder needs to be clarified.