How much blue light should an IOL transmit?

Abstract

Older, and even some modern, intraocular lenses (IOLs) transmit potentially hazardous ultraviolet radiation (UVR) to the retina. In addition, IOLs transmit more blue and green light to the retina for scotopic vision than the crystalline lenses they replace, light that is also potentially hazardous. The severity of UVR-blue type phototoxicity increases with decreasing wavelength, unlike the action spectrum of blue-green type retinal phototoxicity and the luminous efficiency of scotopic vision which both peak in the blue-green part of the optical spectrum around 500 nm. Theoretically, UVR+blue absorbing IOLs provide better retinal protection but worse scotopic sensitivity than UVR-only absorbing IOLs, but further study is needed to test this analysis. UVR is potentially hazardous and not useful for vision, so it is prudent to protect the retina from it with chromophores in IOLs. Determining authoritatively how much blue light an optimal IOL should block requires definitive studies to determine (1) the action spectrum of the retinal phototoxicity potentially involved in human retinal ageing, and (2) the amount of shorter wavelength blue light required for older adults to perform essential activities in dimly lit environments.

Figure 1

A_λ and B_λ describe how UVR-blue type phototoxicity varies with wavelength in an aphakic and a phakic eye, respectively. V’_λ and V_λ are the relative spectral luminous scotopic and photopic efficiencies, respectively, of the standard CIE observer. They characterise how scotopic and photopic visual sensitivity vary with wavelength in a normal phakic eye.

Figure 2

The percentage spectral transmittance of crystalline and intraocular lenses listed in Table 1. Spectral transmittance data on 20D UVR-only absorbing IOL 1 (Alcon AcrySof MA60BM) and 2 (Pharmacia & Upjohn 720A) 20D lenses are from Lin, et al. UVR+blue absorbing IOL data (Alcon AcrySof Natural 20D lens) are from Mr Raphael Chan, Alcon Surgical Division, Forth Worth, TX, USA. The 53 and 75 year old crystalline lens transmittance data are from Boettner and Wolter.