Fig. 8.51 Light transmission spectrum of a 20 diopter AcrySof Natural IOL compared to a 30 year old and 40-year-old human crystalline lens and a 20 diopter colorless UV-blocking IOL [36]

increased blue hues seen by patients who have received colorless UV blocking IOLs [37]. Hoya introduced blue light filtering IOLs in Japan in 1991 (three-piece PMMA Model HOYA UVCY) and in 1994 (singlepiece PMMA Model HOYA UVCY-1P). The blue light filtering characteristics of the HOYA and the AcrySof Natural differ only slightly. Clinical studies of these blue light filtering IOLs have been carried out in Japan. One study found that pseudophakic color vision with a yellow-tinted IOL approximated the vision of 20-year- old control subjects in the blue light range [38]. Another study found some improvement in photopic and mesopic contrast sensitivity, as well as a decrease in the effects of central glare on contrast sensitivity, in pseudophakic eyes with a tinted IOL vs. a standard lens with UV-blocker only [39].

Recently, Bausch and Lomb introduced the SoftPort AO lens which is designed to block purple light. UV and purple light are considered more toxic than blue light, and it is felt by some that blocking UV and purple light should be sufficient.

Although blue light is known to be less toxic, it has clearly been shown to have deleterious effects and so blocking only purple wavelengths may put the retina at risk.

Summary

Removing the cataractous or noncataractous human lens, removes the eye’s natural blue light filter and exposes the retina to higher levels of blue light, than ever before. IOLs are now available that can filter out much of that blue wavelength light similar to the

normal noncataractous human lens. Purple wavelength blocking IOLs may still leave the retina exposed to blue light.

8.3.4.4Quality of Vision with Blue Light Filtering IOLs

A multi-centered, randomized prospective FDA evaluation of the AcrySof® Natural IOL was carried out before the lens gained approval for use in the USA. Three hundred patients were randomized to bilateral implantation of the AcrySof® Natural IOL or the clear AcrySof Single-Piece IOL. All the patients were screened to ascertain normal preoperative color vision beforebeingdeemedeligibleforthestudy.Postoperative parameters measured, included visual acuity, photopic and mesopic contrast sensitivity, and color perception using the Farnsworth D-15 test. Results demonstrated no difference between the AcrySof® Natural IOL and the clear AcrySof® IOL in any of these parameters. More substantial color perception testing, using the Farnsworth-Munsel 100 Hue Test has also demonstrated that there is no difference in color perception between the AcrySof Natural IOL and the clear AcrySof IOL [40].

Although the contrast sensitivity tests performed under mesopic conditions in the FDA trials demonstrated that the AcrySof® Natural IOL does not negatively affect mesopic vision, some have raised concerns about mesopic and scotopic vision in patients with blue light filtering IOLs, since blue light is imperative for night vision. Mesopic vision begins at approximately 0.001 cd/m2 and extends up to 5 cd/m2 for a 3° diameter centrally fixated target [41]. The upper range could extend up to 15 cd/m2 for a 25° diameter target; however, 3 cd/m2 is the most often cited upper limit for mesopic vision. One can liken this to the low-light conditions on a cloudless night with a full moon. Scotopic refers to light levels below the mesopic range, which can be likened to a moonless, starry night.

Certainly, if all the blue light were blocked, one might expect some decrease in scotopic vision. However, neither the HOYA nor the AcrySof® Natural IOL blocks all blue light. It is well recognized that the most important wavelengths for scotopic vision are at and around 507 nm [42]. The AcrySof® Natural IOL allows transmission of approximately 85% of light at