The Zeaxanthin and Visual Function Study

Replicate measures of foveal 1 degree estimated central MPOD were evaluated with the Quantify® MPS 9000 macular pigment screener, a modified heterochromic flicker photometer (HFP). It employs alternating blue and green flickering LED's and fixation on a 1 degree target, so that a representative measurement at 0.5 degree off center from the fovea is calculated. The method has good repeatability (r = 0.97) and the data are comparable with an objective optical method based on retinal reflectometry (r = 0.78).

Replicate measures of foveal 1 degree estimated central MPOD were evaluated with the Quantify® MPS 9000 macular pigment screener, a modified heterochromic flicker photometer (HFP). It employs alternating blue and green flickering LED's and fixation on a 1 degree target, so that a representative measurement at 0.5 degree off center from the fovea is calculated. The method has good repeatability (r = 0.97) and the data are comparable with an objective optical method based on retinal reflectometry (r = 0.78).

Replicate measures of foveal 1 degree estimated central MPOD were evaluated with the Quantify® MPS 9000 macular pigment screener, a modified heterochromic flicker photometer (HFP). It employs alternating blue and green flickering light emitting diodes and fixation on a 1 degree target, so that a representative measurement at 0.5 degree off center from the fovea is calculated.

We determined the target deformation detection thresholds, or amplitude of the minimum detectable distortion of a 1 degree foveal circular target. The peak spatial frequency of RF (radial frequency) patterns was 5 cyc/deg; the radial modulation frequency was 8 cyc/360°; mean radii were 0.5°, 1°, 2.0°, or 2.5°; and stimulus contrast was 80%. The highest % modulation score possible is 0.13 while the easiest (lowest score) was 10% modulation.

Black and 10% contrast near reading visual acuity was assessed with a Colenbrander Mixed Contrast Reading Card with LogMAR letters (#4031, Precision Vision, LaSalle, Illinois). We determined single letter acuity on an ordinal VAS (Visual Acuity Scale). The largest letters were 0.05 LogMAR with a VAS = 35 while the most difficult smallest letters were LogMar 1.25 or VAS 105. The test card was held at 40 cm with best monocular refraction, and both low and high contrast letter acuity were assessed.

Photostress glare recovery test involves exposing an individual eye to intense light, or retinal bleach, for a set duration of time and measuring the time taken for visual acuity to recover to a predetermined level. Glare photo-stress recovery (in seconds) following 30 seconds of continuous retinal bleach, was assessed using 2 line supra-threshold low contrast randomly presented Landolt Cs using the KOWA AS14B Night Vision Tester (KOWA Optimed, Tokyo, Japan).

Distance photopic contrast sensitivity function (CSF) at 5 spatial frequencies (1.5, 3, 6, 12 & 20 cc/deg) was determined with the Functional Vision Analyzer® (Stereo Optical Co, Inc, Chicago, IL). Contrast sensitivity readings are shown as a curve. Visual acuity is plotted along the horizontal axis and contrast sensitivity along the vertical axis. Among the normally sighted people, both visual acuity and contrast sensitivity have a wide range of variation.Low population CSF is 0-200 units; normal population CSF is 200-300 units and suprathreshold CSF is 300+ units.

The ChromaTest© is a computerized psychophysical test of protan and tritan color thresholds against age-corrected data. The computer finds the endpoint of the test by a Modified Binary Search method; if response is correct, on the next presentation the color difference between letter and background is halved. If response is incorrect, the color -contrast is doubled. Incorrect responses prolong the test, but do not influence the final threshold. This method of determining thresholds leads to finite steps which reach a plateau at the color contrast sensitivity threshold.

Scotomas within the central 20 degree central macula visual field sensitivity was assessed at 5 contrast levels (20, 40, 60, 80, and full contrast). A yellow wavelength stimulus avoided confounding by the lens. Subjects outlined the boundaries of their scotoma(s) on an area-integrating and recording touch flat- screen RGB monitor displaying a central fixation point and movable horizontal/vertical raster lines. The computer calculated summed area of the scotoma(s) with arbitrary scaling from 6000 (dense scotoma) to 0 relative units (absence of scotoma).