Graefe’s Arch Clin Exp Ophthalmol(2006) 244: 1562–1564 GUEST EDITORIAL

DOI 10.1007/s00417-006-0336-0

Sebastian Wolf

Received: 6 March 2006Accepted: 12 March 2006Published online: 27 April 2006# Springer-Verlag 2006

Macular pigment measurements: which methodshould we use?

Macular pigment (MP) was investi-gated as early as 1866, when MaxSchultze concluded that there is afunctional connection between the“yellow spot” in the retina and theabsorption of blue light. He stated thatMP may provide protection againstthe hazard of short-wavelength visiblelight. MP consists of the two hydroxy-carotenoids lutein (L) and zeaxanthin(Z) and is of is of alimentary origin.Human MP is detectable in the wholeretina, but the highest concentrationsare found in the fovea [17]. As manyantioxidative properties are attributedto the MP, it has been investigated inrespect to its role in the pathophysio-logy of age-related macular degenera-tion (ARMD). The properties of MPinclude a high capacity to absorb short-wavelength blue light [19]. The peakof the MP absorbance spectrum is at460 nm and works as a broad-bandfilter for the macula. Two advantagesare achieved: (1) the macula’s opticalaccuracy is improved [11, 16] and (2)the damaging photooxidative influ-ence on the neurosensory retina isreduced. In the photoreceptor outersegments, the antioxidant effect ofL and Z is the essential mechanism[1, 22]. The antioxidant propertiesenable the carotenoids to neutralizefree radicals.

The optical and antioxidant proper-ties of MP, its possible relation to thepathophysiology of ARMD, and thepossibility to modify macular pigmentoptical density (MPOD) by nutritional

supplementation have resulted in agrowing interest in research on MP.This is reflected by a growing numberof papers on MP during recent years.

MPOD can be measured by psy-chophysical and optical means. Theseinclude heterochromatic flickerphotometry [12, 24] and minimummotion photometry [23], Ramanspectrometry [8, 9, 14], imagingreflectometry [3, 13], reflectometry[4, 27], and autofluorescence spectro-photometry [12] and imaging [6, 23,26]. This large number of differentmethods may explain the inconsisten-cies between papers on MPOD inpatients with various stages of ARMD[1, 2, 5, 7, 10, 15, 16, 18, 19, 21, 24].The current issue presents a paper inwhich Trieschmann et al. [25] presentMPOD measurements using autofluo-rescence images. They compare amethod [27] based on pioneering workfrom Delori et al. [12] using autofluo-rescence images obtained at twowavelengths (488 nm and 514 nm) bymeans of a method presented by thesame group previously [23, 26] usingautofluorescence images obtained atone wavelength (488 nm). Theydescribe in great detail the theory ofMPOD measurements using autofluo-rescence imaging, repeating previouswork [12]. In their manuscript theyconclude that the one-wavelengthmethod is adequate for visualizing theMP but not for determining MPOD,whereas the two-wavelength methodallows for accurate determination of

S. Wolf (*)Klinik und Poliklinik fürAugenheilkunde, Inselspital,Universität Bern,3010 Bern, Schweize-mail: sebastian.wolf@insel.ch

MPOD. These conclusions are mainlybased on the theoretical considerationspresented in the methods section.However, the actual measurementspresented in the paper do not permitthese conclusions. There is noevidence that one method is better thanthe other, since no comparison with anindependent measure of MPOD basedon a more established technique suchas psychophysics is presented in themanuscript. However, recently acomparison between the two-wave-length method using autofluorescenceimaging (AF) and the heterochromaticflicker photometry (HFP) technique

has been published [20]. In this paperno correlation between the two meth-ods was presented. However, the largedifference in the coefficient of varia-tion for repeated measurement be-tween the two methods (16.6% forHFP vs 3.3% for AF) suggests that thetwo-wavelength AF method is moreprecise than the HFP method fordetermination of MPOD [20].

Recent work suggests that the dis-tribution of MP could be moreimportant than central MPOD [6, 18,23]. Therefore, future studies on MPshould use a method allowing mea-surement not only of MPOD in the

foveal center but also of MP distribu-tion. Since the determination of MPdistribution with psychophysicalmethods is difficult and very timeconsuming, MPOD measurement byimaging methods appears to be moresuitable for clinical studies. The the-oretical considerations presented inthe paper by Trieschmann et al. [25]suggest that we should abandon theone-wavelength AF method and useonly the two-wavelength method forfuture studies.

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