Evaluation of a novel instrument for simultaneous measurement of macular pigment and lens optical density, and lens equivalent age

Abstract

Purpose: To evaluate a novel heterochromatic flicker photometer (HFP), MAPCATsf™, for precise measurement of, and comparison between, macular pigment optical density (MPOD), lens optical density (LOD) and lens equivalent age (LEA).

Methods: The MAPCATsf is a LED-based HFP providing centrally fixated, 1.5° and 14° diameter stimuli alternating between blue (455 nm) and green (515 nm). With the 1.5° stimulus, subjects adjust the blue LED intensity to produce a flicker null. With the 14° stimulus, they adjust the blue LED intensity to eliminate flicker around the periphery. Typically 5 blue LED intensity settings for each stimulus, as well as the fixed, green LED intensity, are recorded by a photodiode detector. A microprocessor computes the subject's LOD-corrected MPOD, LOD (at 425 nm) and LEA, the latter two based on a model proposed by Sagawa et al. [J. Opt. Soc. Am. A 18, 2659 (2001)]. Fifty five naïve and mostly younger subjects (av. 37 yr) in Miami, FL were tested twice to evaluate test-retest repeatability of the instrument. An additional group of 131 mostly older subjects (av. 68 yr) in San Diego, CA were tested once.

Results: A Bland-Altman plot of the test-retest MPOD data provided an average difference between the 2 consecutive measurements of 1.94 ×10^-3, and limits of agreement (± 1.96 SD) of ± 0.079. Corresponding results for LOD and LEA were -0.012 ± 0.090 and -0.5 ± 6.7 yr respectively. For the younger Miami group, MPOD increased with LEA at an average rate of 0.0063 yr^-1 (R² = 0.21, p < 0.001) whereas for the older San Diego group, it decreased at an average rate of 0.0035 yr^-1 (R² = 0.275, p < 0.0001). Similar results were obtained when comparing MPOD with LOD.

Conclusions: The test-retest results for the MAPCATsf were superior to those reported for other instruments for MPOD measurement. Among the older subjects, it is possible that higher carotenoid consumption in the diet leads to a higher MPOD, as well as a lower LEA resulting from a higher carotenoid content in the lens. Among the younger subjects, the positive correlation between MPOD and LEA may simply reflect an improving diet with age (LEA being an approximate surrogate for biological age).

Keywords: 587 macular pigment • 444 carotenoids/carotenoid binding proteins • 413 aging