20/07/2016
Author: Cari Pérez Vives, PhD, Medical Affairs, Alcon Management (Switzerland)
The Ultraviolet (UV) radiation belongs to the short wavelength range (100-400 nm), which is not visible for the human eye. Short-wave radiation (UV-C) is almost completely filtered out by the atmosphere and the ozone layer, reaching the earth just in small amounts. It is well known that the UV radiation is harmful for the human eye, which is exposed to high levels of radiation from light. The intensity of the sunlight which the eye is exposed depends on the wavelength of the light, latitude, altitude, season, time of the day and weather conditions.
Due to the filter properties of the cornea, aqueous humor, lens, and vitreous body, the retina in an adult eye with a natural lens appears to be protected against phototoxic UV light in the range 200-400 nm. The natural lens absorbs wavelength from 300 nm to 400 nm; this absorption of high energy radiation leads to the photo-oxidative processes in the lens, which leads to the formation of yellow-brown pigments, changing the transmission characteristics of the natural lens with aging. Nevertheless, after cataract surgery, the natural lens and therefore the protection of the retina against UV-B and above all UV-A light is removed, leaving the eye more sensitive to phototoxic damage.
Until the mid-80’s IOLs had no UV filter, which meant that the retina was exposed to UV-Light to an extent like never before in lifetime, following cataract surgery and IOL implantation. More UV light than ever before surgery was able to reach the retina. There are in-vitro, animal data and clinical studies reporting cell damage and death, and higher incidence of macular edema in those eyes implanted without UV-blocker IOLs. Nowadays, all IOLs in the market have UV filter, but not all of them filter the UV in the same way. It has been reported that IOLs should provide a complete UV protection; several studies recommend a maximum transmission of 10% at close at 400 nm, in order to ensure adequate UV protection following cataract surgery.
In this study the spectral transmission curves of 5 commercialized IOLs were measured in vitro, mainly focus on the UVA and UVB interval (290-380 nm). The transmission curves of the IOLs were obtained by using a Perkin-Elmer Lambda 800 UV/ VIS spectrometer. This apparatus can measure the spectrum from 200 nm onwards, which means that spectral transmission in UVA, UVB and part of UVC are accurately determined (precision is up to 1 nm). The air was taken as a reference to measure transmittance. Figure 1 shows the transmission curves of 5 different IOLs in the market. IOL 1 and 4 showed the better transmission outcomes, almost reaching 10% of transmission at 400 nm (396 and 398 nm, respectively). In contrast, IOL 3 showed the worst results having 10% of transmission at 360 nm. Due to study design challenges, clinical evidence for the effectiveness of IOL UV filter in reducing the incidence of retinal disorders has not been established yet. But, as UV light can damage retinal structures, a UV-blocker IOL with maximum transmission of 10% close to 400 nm should be implanted after cataract surgery in order to guarantee UV protection of the retina after the cataract operation.
Figure 1: Transmission curves of 5 different IOLs in the market.