Richard Bone

Richard Bone

Professor Richard Bone received his B.Sc. in Mechanical Engineering from the University of Bristol, UK in 1965. He spent a brief period at the University of Reading, UK as a research assistant under Robert Ditchburn where he first developed an interest in macular pigment. In 1967, he moved to the University of the West Indies (UWI) in Jamaica and completed his Ph.D. in biophysics working under the direction of John Sparrock. He remained at UWI. as a faculty member until 1980 when he joined the Department of Physics at Florida International University where he is currently a Professor. He published his first paper on the topic of the macular pigment in 1971 and has continued to work and publish in this field throughout the intervening years. His important contributions, in collaboration with Professor John Landrum, include the first definitive identification of the macular pigment, the distribution of its components, lutein, zeaxanthin, and meso-zeaxanthin, in the retina, the first study on the effects of lutein supplementation on macular pigment optical density (MPOD), and the first comparison of macular pigment in healthy and AMD eyes. His most recent contribution has been the development of a subject-friendly heterochromatic flicker photometer for simultaneous MPOD and lens density measurement.

Coloured Filters in the Eye 2006: Macular Pigment Optical Density Determined by Reflectometry and Flicker: Is Flicker the Gold Standard?

Heterochromatic flicker photometry (HFP) is often regarded as setting the standard with which other methods of determining macular pigment optical density (MPOD) should be compared. We have developed a reflectometry method employing a retinal camera modified with multi-bandpass filters that provides the reflectance of the retina at a number of specific wavelengths. Based on a simple model of sequential absorbers (MP, cone and rod photopigments, and melanin), image analysis software is employed to derive the optical density distribution of the MP. We have tested the procedure on a group of 15 subjects in the age range 18 to 24, whose MPOD was also determined by HFP. We found a less than perfect correlation (R2 = 0.65, P < .001) between MPODs obtained by the two methods that led us to re-examine one of the basic assumptions of HFP. It is assumed that photoreceptor relative spectral sensitivity is the same for the foveal and parafoveal locations where measurements are made. Preliminary data indicate that this may not be a valid assumption. We modified the flicker photometer to determine the complete MPOD spectrum from 410 to 680 nm. The spectrum should be essentially flat with an OD of zero above ~ 540 nm, yet we found for the 3 subjects tested an apparent OD increasing with wavelength from zero at ~ 560 nm and, in one of the subjects, reaching a value of ~ 0.3 at 680 nm. This suggests that the LWS/MWS cone ratio may be significantly lower, at least in some subjects, in the fovea than in the parafovea. The result would be a decreased sensitivity to longer wavelengths in the fovea, equivalent to the effects of an absorbing pigment. It is possible that, from these measurements, we could determine the LWS/MWS cone ratio in the fovea relative to the parafovea and make appropriate corrections to the MPOD spectrum.

 

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