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Michael G Quigley, Ian Powell, Walter Wittich; Light and age-related macular degeneration (AMD): retinal light dose or irradiance ( RI) varies inversely with axial length as does AMD risk. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4981.
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The role of light in the genesis and evolution of age-related macular degeneration (AMD) is controversial. Although a meta-analysis of studies attempting to link ambient sunlight exposure to AMD showed there to be a link, there remains some uncertainty ( Sui GY, BJO 2013). However ambient light exposure is only a proxy for (RI) because pupil size,hats,sunglasses,and immeasureable behaviour modifications such as gaze aversion and lid closing will alter the retinal light dose. Short axial length increases significantly AMD risk with each millimeter decrease in axial length being associated with a 29% increased risk of early AMD ( Pan CW et al.,Ophthalmology 2013). We calculate retinal light dose (RI) in a normal population from the Reykjavik Eye Study ( Olsen T et al., Acta Ophthalmo Scand 2007) and correlate it with axial length.
We created a simple one-surface schematic eye to calculate light flux through the pupil and resultant image size on the retina. Pupil size is known to be unaffected by refractive error ( Winn B et al., IOVS 1994). From this information, the retinal light dose (photon equivalents)/mm can be calculated. The calculations were then transposed to a two dimensional retina for photons/mm2 (RI).These results were then verified using the ray-tracing feature inside the optical-design software Opticsoft II ( Powell I, Appl Opt 1978).
Retinal irradiance is inversely proportional to axial length ( r=0.95). A 21mm axial length eye would always be receiving 17% more photons/mm2 compared to a 23mm axial length eye and 42% more compared to a 25mm axial length eye.
Retinal irradiance is inversely proportional to axial length and short axial length eyes would constantly be receiving a significantly higher light dose compared to long axial length eyes. AMD risk is also inversely proportional to axial length. The parsimonious explanation for this relationship is that light plays a role in the genesis and evolution of AMD as is theorized (Hollyfield JG, IOVS 2010).
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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