MinireviewHeterochromatic flicker photometry
Section snippets
Instrumentation
The heterochromatic flicker photometer used in our studies is typical and will be described in detail. It is shown schematically in Fig. 1. A single 150 W quartz-halogen lamp is the source for the two components of the visual field. The advantage of a single source is that variation in the light output due to voltage fluctuations, aging of the lamp, etc., will affect both components and, to some extent, will be self-canceling. Lenses, mirrors, and interference filters are used to form
Results
Data from a group of 17 novices are presented in Fig. 2 in the form of a comparison between MPOD in their left and right eyes. The graph illustrates the typical SDs referred to earlier, as well as the similar optical densities that are usually measured by HFP in a subject's left and right eyes [10]. Fig. 3 shows a series of measurements made over a ∼6 month period by a highly experienced subject whose SD never exceeded 0.02. The day-to-day variability clearly exceeds the SD, but it is not clear
Discussion
There are several advantages of HFP as a method for determining MPOD. The method has been validated by the HFP-generated absorbance spectrum of the macular pigment which matches very closely those of lutein/zeaxanthin mixtures in appropriate lipid environments. Through the use of a reference (extra-foveal) measurement as well as a reference wavelength (540 nm), the results are independent of absorption or scattering in the optic media. With appropriately designed instruments, MPOD data can be
Acknowledgements
This work was supported in part by NIH Grant GM 08205.
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