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E. DeHoog, J. Schwiegerling; Position of White Light Best Focus in the Human Eye. Invest. Ophthalmol. Vis. Sci. 2007;48(13):993.
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To determine the wavelength that corresponds to the position of "white" light best focus for optical design purposes.
A Badal optometer was used to present two sources to a series of subjects. One source had a monochromatic output, while the other source was a halogen white light source. The monochromatic source was varied from 15 different wavelengths across the visible spectrum, ranging from 420 nm to 700 nm. The subjects first moved the white source into focus and then shifted the monochromatic source, so that it was in focus simultaneously with the white light source. The adjustments were repeated for the 15 test wavelengths. A total of 20 subjects were tested.
Due to longitudinal chromatic aberration within the eye, the different monochromatic sources appear at different object vergences relative to the white light source. These vergences correlate well with the previous clinical measures of ocular chromatic aberration, with all measurements with +/-0.2 diopters of the theoretical dispersion curve of the eye. This technique locates the position of the best-focus for white light in terms of a monochromatic equivalent wavelength. In general, the white light best focus occurs at a monochromatic equivalent wavelength between 590-610 nm.
In designing ophthalmic optics, a design wavelength of 555 nm is often used since it is the peak of the photopic response. However, these results suggest that a more appropriate desgin wavelength would be closer to 600 nm if the optics are to be used under polychromatic conditions.
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