Date of Award

Fall 2004

Project Type

Dissertation

Program or Major

Psychology

Degree Name

Doctor of Philosophy

First Advisor

Ken Fuld

Abstract

Two carotenoids, lutein and zeaxanthin, accumulate in the central retina where they are collectively referred to as macular pigment (MP). By absorbing short-wavelength light, MP may attenuate photophobia (PP)---visual discomfort induced by normal light exposure---for targets composed of short-wavelength light. The aim of this study was twofold: first, to investigate a possible relationship between integrated macular pigment optical density (MPOD) and PP thresholds for short-wavelength targets relative to mid- to long-wavelength targets; and second, to measure changes in PP thresholds after increasing MP with lutein supplements.

MPOD was measured psychophysically at 20', 30', 60' and 120' eccentricity with a Macular MetricsRTM densitometer. Each subject's MPOD profile was fit with a Gaussian and Lorentzian function and the area under the curve was calculated to yield an integrated Gaussian MPOD (iGMPOD) or integrated Lorentzian MPOD (iLMPOD). PP thresholds for two foveal and two parafoveal, 8.2-degree targets were measured using a Maxwellian-view optical system. At both loci, a scaling technique was used to measure subjects' level of discomfort for a short-wavelength broadband (blue) light, which was strongly absorbed by MP, and a mid- to long-wavelength broadband (orange) light, which was not absorbed my MP. For both eccentricities, the log relative energy necessary to induce PP for the blue target was subtracted from the log relative energy necessary for the orange target. The foveal value was then subtracted from the parafoveal value to yield a PP ratio. PP ratios and iGMPOD and iLMPOD were calculated for ten subjects. Repeated measures were obtained for four of these subjects after six weeks and twelve weeks of consuming 60mg of lutein ester supplements per day.

PP ratios were positively correlated with iGMPOD (r = 0.830, p = 0.002) and iLMPOD (r = 0.775, p = 0.008). According to a subjects-by-trials design, both iGMPOD (F = 9.12, p = 0.015) and iLMPOD (F = 17.35, p = 0.003) significantly increased from baseline. Significant increases in integrated MPOD corresponded to significant increases in PP ratio (F = 10.41, p = 0.036).

The results suggest that MPOD may influence the amount of short-wavelength light necessary to elicit PP. Further, PP thresholds for short-wavelength lights can be increased by augmenting MPOD with lutein supplementation.

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