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Introduction
The effects of estrogen on human physiology are pervasive, involving systems and organs not directly concerned with reproduction and sexual behavior (Gruber et al., 2002; Nilsson & Gustafsson 2002). Estrogen has been shown to exert multiple effects on neural function and the brain even outside the hypothalmic/pituitary axis of the female menstrual cycle (McEwen, 2002). Estrogen receptors are found within the brains of both sexes (Zhang et al., 2002), and, indeed, estrogen receptors have been reported to be present in the retinas of men and women (Munaut et al, 2001). However, the role of estrogen receptors for vision remains unknown. By measuring visual sensitivity across the human menstrual cycle for a range of background light levels for several visual mechanisms, the present study sought to lay the groundwork for subsequent studies concerning the roles of retinal estrogen receptors specifically. A more immediate aim was to provide an increased understanding of the menstrual cycle itself, which involves the rise and fall of a number of sex steroid hormones and gonadotropins, most notably estrogen, progesterone, follicle stimulating hormone (FSH), and lutenizing hormone (LH) (Speroff et al., 1999).
There have been many studies of visual changes related to the menstrual cycle [see review by Guttridge (1994)]. However, almost all of these studies, with a few exceptions (e.g.Yilmaz et al., 1998) predate the first reports of retinal estrogen receptors (Kobayashi et al., 1998; Ogueta et al., 1999), and many of the menstrual-cycle studies were concerned mainly with changes in subjects' arousal or attention levels (Guttridge, 1994). There has been relatively little emphasis on changes that are likely to be retinally based, and there appear to be no studies evaluating the effects of the menstrual cycle on the adaptation properties of distinct photopic visual mechanisms. The present study was conducted to address these omissions. Young healthy women were tested psychophysically 5 days per week across successive menstrual cycles.
The design of the present study took into account the results of a clinical study in which administration of the selective-estrogen-receptor-modulator tamoxifen was shown to affect visual thresholds mediated via short-wavelength-sensitive (SWS) cones (Eisner et al., 2004). For that study, there was evidence that tamoxifen affected the adaptation properties of SWS cone pathways. The subjects were middle-aged women who used...