While there are conflicting schools of thought on the role of blue light filtration vis-a-vis Intra Ocular Lens, proponents of blue light filtration may look towards the role of blue light filtration towards improving Macula Pigment Optical Density (MPOD).
To this school of thought, one of the most important benefits of filtering short wavelength blue light is to protect the macula pigment and thereby increase the Macula Pigment Optical Density (MPOD). Unfortunately, though the macula pigment plays a crucial role in protecting human vision, yet this is one of the least talked subject.
Strangely, macula pigment and its importance was not a discovery of recent times, but dates back to the works of Max Schultz in the 19th century, who theorized that the yellow spot absorbed blue light. Many decades later, G Wald, during the 40s of the last century hypothesized that the macula pigment was consisting of specific caratenoids. Later in the 1980s, Bone et al, Ham et al, and various other studies concluded that the macula pigment consist of Lutien and Zeaxanthin, and has a definite role to play in human vision.
What is Macula Pigment ?
Human macula pigment consists of lutein and zeaxanthin. They reach their greatest concentration in the fovea and diminish as you move further away from the fovea to the peripheral retina. However, though the caratenoids are concentrated in this region, lutein and zeaxanthin are found in the whole of the retina.
What specific benefits are attributed to Macular Pigment ?
Extensive research starting with G Wald to modern day studies have indicated multifaceted beneficial role of the macula pigment. The absorbance power of macular pigment of the blue light peaks at the 460 nm of wavelength of light, and therefore reduces the sensitivity of the macula region to short wavelength of light by acting as a pre retinal filter. The fovea has the greatest visual acuity of all retinal regions because of its close cone receptor cells spacing. This however makes the fovea vulnerable to any form of image degradation that may result from higher order aberrations, one of which is chromatic aberration. In 1866, Schultze first indicated that the image degrading effect of chromatic aberration may be mitigated by the filtering properties of macula pigment by preventing the short wavelength blue light reaching the cone cells. This was later corroborated by G Wald. In short, macula pigment helps the eye to minimize the effect of chromatic aberration, thus reducing its effect on human vision.
Other Benefits -
The macula picgment also has antioxidant properties. The generation of reactive oxygen species can occur as the byproduct of cellular metabolism or as the result of photo chemical reactions. These are free radicals, which are partially reduced oxygen species containing one or more unpaired electrons. These molecules are highly reactive which can result in cell death. The retina may be particularly susceptible to damage by free radicals. The macula pigment may act to protect the retina by acting as a free radical scavenger and reducing the effect of photochemical damage.
Glare is a common phenomenon among many old age patients suffering from retinal problems. Studies like the Beaver Dam have indicated the close relation between lower macula optical density levels and glare phenomemon.
What is the role of blue light filtration and macula pigment ?
If macula pigment is so important for healthy vision , then it may be important to protect the macula pigment and help have a healthy macula pigment optical density (MPOD). In a study by John M. Nolan , published in the Investigative Ophthalmology; Science Journal in 2009 the role of blue light filtering IOL in augmenting MPOD levels was proved. The MPOD levels were measured by hetero chromatic flicker photometry. The basic science behind this technique is to ask the patient to observe a light stimulus that altered between a wavelength band that absorbed the macula pigment and one that was not. The patients were asked to adjust the radiance of the wavelength band absorbed by macula pigment to minimize their perception of flicker . This gives an idea of the macula pigment of the patient. Several commercial devices are also now available that measure macula pigment optical density levels.
The proponents of blue light filtering IOLs often link the benefits of blue light filtration to retinal health in the form of arresting programmed cell death of the retinal pigment epithelium. While that line of argument is often talked about, less light is shed on the connection between blue light filtration and healthy levels of macula pigment optical density, post cataract surgery.