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Posterior Segment
the total number of foveal cones is also normal.
3
Thus, a Conclusion
combination of shortened outer segments with, in cases of large Probing the unique property of the directionality of the cone
drusen, cone disarray is the probable cause of the decline in photoreceptors increases our insight into their integrity in the
directionality in early AMD. Malfunctioning of the underlying retinal various stages of retinal diseases. In AMD, directionality is reduced
pigment epithelium is probably the basis for this. at an early stage, pointing to malfunction of the outer segments.
The additional feature of spectral analysis of the reflected light
Macular Pigment adds information about what happens to ocular absorbers in retinal
As a fringe benefit of this study on directionality, spectral analysis disease. The amount of macular pigment seems rather robust. n
showed that in early AMD the amount of macular pigment was not
different from normal. Earlier findings demonstrated that there is
Dirk van Norren recently retired as a (part-time)
no age effect either. These are interesting findings in light of the
Professor in Ophthalmic Physics in the Department of
messages from industry suggesting that taking supplements Ophthalmology at University Medical Centre Utrecht. A
containing lutein or zeaxanthin is helpful in preventing eye disease.
few years earlier he retired from his main occupation:
Director of the TNO Human Factors Institute in
Indeed, lutein and zeaxanthin are the constituents of macular
Soesterberg in The Netherlands; prior to this position he
pigment, and ingestion generally increases their optical density in was Director of the National Aerospace Medical Center
the retina.
4
However, in this study at least there proved to be no
in Soesterberg in The Netherlands.
relationship between the amount of macular pigment and the
Martijn Kanis is an intern in ophthalmology at University
prevalence of early AMD. That macular pigment was low in late AMD
Medical Centre Utrecht, where he recently completed
seems not very surprising. The foveal cones are heavily damaged his PhD research. He defended his thesis in September
and thus the number of binding sites of macular pigment is
2008. Before that he studied medicine at Antwerp
University, Belgium.
probably reduced. Much is still unknown about the function of
macular pigment. Whether a high optical density of macular
pigment helps to prevent AMD or other eye diseases is one of the
unanswered questions.
1. Kanis MJ, et al., Foveal cone-photoreceptor integrity in nondirectional spectral reflection from the human fovea, 37:1236–49.
aging macular disorder, Invest Ophthalmol Vis Sci, 2008;49: J Biomed Optics, 2008;13:024010. 4. Van de Kraats J, et al., Lutein and zeaxanthin measured
2077–89. 3. Curcio CA, et al., Photoreceptor loss in age related separately in the living human retina, Invest Ophthalmol Vis
2. Van de Kraats J, van Norren D, Directional and macular degeneration, Invest Ophthalmol Vis Sci, 1996; Sci, 2008;49(12):5568–73.
Editor’s Recommendations
Directional and Nondirectional Spectral Reflection pathway. The mean density of the macular pigment of a
from the Human Fovea subgroup (53 subjects, 19–75 years of age) correlated
van de Kraats J, van Norren D, J Biomed Opt, 2008;13(2):024010.
significantly with independent data from reflectance and
A model of the directional and non-directional reflection autoflourescence images obtained by scanning laser
spectrum of the human fovea is developed, incorporating ophthalmoscope (SLO) and data from flicker photometry. n
reflectors, absorbers and a wavelength-dependent optical
Stiles-Crawford effect (OSCE). Optical Density of the Aging Human Ocular Media in the
Visible and the UV
Data from 102 healthy subjects between 18 and 75 years of age
van de Kraats J, van Norren D, J Opt Soc Am A Opt Image Sci Vis, 2007;24(7):1842–57.
obtained with the fundus reflection analyser (FRA), an imaging The authors analysed the literature on the absorption in the
spectrograph that measures the directional reflection profile of young and aging human eye media. Five templates were derived
the human fovea in the pupil plane from 400 to 950nm, were to provide an adequate description of the spectra from 300 to
analysed. Subgroups of young (<40 years of age) and old (>50 700nm for the lens, cornea, aqueous and vitreous.
years of age) observers were defined. The mean results of the
young group defined a template for directionality versus Two templates were found in all media. They stand for Rayleigh
wavelength. For the whole group, mean reflection at 550nm scatter and the absorbance of tryptophan. Three additional
from the cones was 2.12%, from the retinal pigment epithelium templates for the lens represent absorbance in kynurenine
0.56% and from the choroid 7.92%. Lens density, cone disc derivatives, such as 3-hydroxykynurenine glucoside (3HKG), and
reflection and blood layer thickness showed significant trends absorbance in two substances found at older age. Except for
versus age. Rayleigh scatter, all templates have a Gaussian shape.
The model for the first time simultaneously describes the Ageing-trend functions were derived that show a linear slope on
spectra of the directional and non-directional reflection of the an age-squared scale. The result can be used to correct for
human fovea. Rayleigh scatter losses of the media and in pre- media losses in visual perception tasks, in fundus reflectometry
retinal layers were assumed to be zero in the non-directional and in studies on light damage. n
70 EUROPEAN OPHTHALMIC REVIEW