Eyeworld

Understanding how the light spectrum functions is necessary to understand how vision works in older patients A s a neuroscientist but a vision scientist as well, un- derstanding vision and how the brain perceives images is the basis for my research. It is common to regard vision strictly in terms of glasses, or refractive errors. Yet for the vast majority of human history, refractive conditions like astigmatism and myopia were very rare. The eye evolved to deal with the challenges posed by the natural envi- ronment such as bright light and seeing at a distance through veiling haze. This is why so many species have developed in- ternal ocular filters to aid vision under ecological conditions. Given the prepon- Clinical update on blue light filtering and aspheric technologies 2 derance of blue light in our atmosphere (via Rayleigh scat- ter), those filters are inevitably blue-ab- sorbing and appear yellow in color. In humans, this filtering is done by the yellow macular pigments (chromophores accumulated from the dietary intake of green leafy vegetables) and the natural yellowing that occurs with the crystalline lens. 1 What the pigments do Vision researchers have intensively studied the effect of the macular pigments on daily vision. It has been doc- umented that these pigments improve visual function by reducing the deleterious effects of intense light. 2 The pigments reduce disability and the discomfort caused by bright light that is largely driven by the blue portion of the visible spectrum. By absorbing very intense light, they reduce the amount of time it takes to recover from short intense light exposures (photostress recovery). They may also aide object detection by improving chromatic contrast (accentuating a colored border by absorbing one side more than the other). By similar mechanisms of strategic filter- ing, they improve visual range (how far one can see). This is done by absorbing the biggest limiter of distance vision, Blue light filtration: What is the evidence today? continued on page 3 by Billy Hammond, PhD which is veiling due to blue haze. When Alcon (Fort Worth, Texas) de- veloped its AcrySof IQ lens, it created an IOL that mimics the spectral absorbance characteristics of the other major yellow chromophore in the human eye, the natural crystalline lens. This was originally done to reduce actinic damage sometimes referred to as the "blue light hazard." Light is, of course, necessary for life and optimal function— for instance, to synthesize vitamin D. However, some vision scientists also believe light has the potential of damaging biologic tissue. 3 Light can convert oxygen to a more reactive form that can, in turn, peroxidize fats (a big problem for fatty tissues like the retina, which are exposed to a lot of light and oxygen). 4 It's believed the energy in light is inversely related to wavelength so shorter wavelengths are more damaging than longer wavelengths; for example, ul- traviolet light is a lot more damaging than infrared. 5 Real world applications Although protection from actinic light may be a strong advantage of blue- absorbing filters, it is likely that natural chromophores like the macular pigments have effects that manifest early in life while an individual is still fecund. Less is better Photostress recovery time

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