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R. Canovas, C. Morini, P. Garcia, R. Rosen; Macular Pigment Density Measurements Using Autofluorescence Technique and Heterochromatic Flicker Photometry . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3808.
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© ARVO (1962-2015); The Authors (2016-present)
Macular Pigment(MP) is believed to have a protective role in the development and progression of Age–related maculopathy(ARM). The goal of our study is to determine wheter the macular pigment density values obtained from modified HRA autofluorescence (HRA) are comparable to that found using the Heterochromatic Flicker Photometry (HFP)technique.
Ten normal age matched subjects had both eyes tested three times with both the HFP and HRA machines. The heterochromatic flicker photometry is a psycophysical way of measuring the spectral sensivity and the MP density of the human eye. The system utilizes blue and green diodes to create targets of varying sizes presented against a blue background. Subjects use a hand control to suppress perceptible flicker of the target. A computer translates the value of this response to produce a filtration density value which correlates to MP density at a specific parameter. This measurement is repeated four times for each target. These values are averaged to give the mean blue light flicker frequency at which the flicker rate of the target is most suppressed for the subject. The blue light frequency is proportional to the amount of MP present.
The modified HRA determines MP density by calculating a MP density Map (MPDM) and comparing foveal and parafoveal autofluorescence at 488nm and 514nm. The MPDM is created by digital substraction of the log autofluorescence images.
The measurements were done in four circle diameters (around 0.25, 0.5, 1.0 and 1.75 degrees) centered on the fovea in both machines.
We recruited 10 normal 29 years old subjects (6 women, 4 men) for the study. Best corrected visual acuity was 20/20 in all of them. Mean MPD for the right eye(OD) in HFP was 0.565±0.14 and HRA was 0.3561± 0.06 (P value 0.0004), for the left(OS) 0.555± 0.09 in HFP and 0.307± 0.06 in HRA ( P value 0.0001)at 0.25 degree. The correlation values in average between HFP and HRA for the were 0.84 OD and 0.75 OS at 0.25 degree.
The results showed highest correlation between the HFP and HRA at 0.25 degrees, probably due to variable distribution of MP away from the central peak
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