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J.M. Stringham, D.M. Snodderly, K. Fuld, A.J. Wenzel; The Effect of Macular Pigment on Photophobia Threshold: Central vs. Peripheral Viewing . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1292.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: 1) To examine differences between photophobia (PP) action spectra derived for central and peripheral viewing conditions. 2) To identify mechanism(s) responsible for any differences. Methods: A Maxwellian–view optical system was employed. Two subjects were used for this experiment. Prior to testing, subjects were dark–adapted to a mesopic–level, maintained by a dimly lit, 16° background field of 0.1 cd/m2. The method of ascending limits was used to determine the minimum radiance of 8° (diam), 5–sec flashes of monochromatic lights required to elicit a criterion squinting response, measured by electromyography. This was done with central fixation and at 11° retinal eccentricity. Results: For both subjects, large but consistent differences in sensitivity were found between central and peripheral viewing conditions. For the peripheral condition, the action spectrum showed a monotonic decrease with increases in wavelength. Above approximately 480 nm, subjects required more energy to reach PP threshold than for the central condition; below 480 nm, the reverse was true. The action spectrum for the central condition, rather than being monotonic, displayed a prominent "notch" with a minimum at 460 nm, which corresponds to the wavelength of peak absorption for macular pigment (MP). The difference spectrum for central and peripheral viewing conditions roughly approximates the MP absorption spectrum. Conclusions: The action spectrum for PP, when unfiltered by MP, decreases with increases in wavelength. This suggests a behavioral mechanism for protection of the retina, as shorter wavelengths are potentially more damaging to biological tissue. For central viewing, which involves filtering by MP, more short–wavelength light is tolerated before PP threshold is reached.
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