Peripheral Light Focusing (PLF)
Peripheral light is difficult to block with the average pair of sunglasses and, surprisingly, it can actually be just as hazardous to eyes as direct sunlight.a–d
Scientists have shown that the corneal dome, acting as a side-on lens, refracts and intensifies peripheral light into concentrated areas of light inside the anterior segment, especially affecting the nasal lens and nasal limbus. This effect, called peripheral light focusing (PLF), has been implicated in the pathogenesis of pterygium and cataract.e–g
Corneal optics focus and intensify rays entering from the temporal periphery onto the nasal lens and nasal limbus.
Measuring PLF in the laboratoryd
Researchers set out to show that secondary images form on the anterior segment of the eye as a result of peripheral light focusing. Light-ray tracing was applied to an anatomically based human eye model with a gradient index crystalline lens. The scientists founds that significant focusing of light was directed to the nasal limbus and the crystalline lens. The concentration levels measured suggest a mechanism for lens phototoxicity. View article
Measuring Ocular PLF in the sunlightc
An anatomically correct eye model was equipped with UVA and UVB sensors at the nasal limbus and was exposed to sunlight in three outdoor environments: urban, mountain and beach. The intensity of UVA radiation at the nasal limbus was the same in all three environments with or without sunglasses, suggesting that the particular sunglasses used in the study (aviator-style) offered no protection from peripheral UVR.
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c Kwok LS, Kuznetsov VA, Ho A, Coroneo MT. Prevention of the adverse photic effects of peripheral light-focusing using UV-blocking contact lenses,. Invest Ophthalmol Vis Sci. 2003;44(4):1501–7.
d Kwok LS, Daszynski DC, Kuznetsov VA, Pham T, Ho A, Coroneo MT. Peripheral light focusing as a potential mechanism for phakic dysphotopsia and lens phototoxicity. Ophthalmic Physiol Opt. 2004;24(2):119–29.
e Coroneo MT, Di Girolamo N, Wakefield D. The pathogenesis of pterygia. Curr Opin Ophthalmol. 1999;10(4):282–8.
f Kwok LS, Coroneo MT. A model for pterygium formation. Cornea. 1994;13(3):219–24.
g Kwok LS, Coroneo MT. Temporal and spatial growth patterns in the normal and cataractous human lens. Exp Eye Res. 2000;71(3):317–22.