Abstract
Purpose: :
Age-related macular degeneration (AMD) is the leading cause of blindness among individuals older than 65 years. Studies have investigated levels of macular pigment (MP) with heterochromic flicker photometry (HFP) which have suggested an increased risk of development of AMD is associated with having reduced MP. There are two compact commercially available HFP instruments in the USA. Our aim was to determine the inter- and intra-instrument measurement variability in a representative clinical population.
Methods: :
Twenty eight patients with and without signs of early AMD over the age of 50 were recruited from the Illinois Eye Institute patient base. Macular pigment optical density (MPOD) measurements were taken using the MacuScope and QuantifEye. Data were collected by a single operator in a single session for each patient. Two measurements were taken on each instrument. If the difference was greater than 0.04 between the two measurements on a single instrument, a third measurement was taken. Paired and unpaired student’s t-tests were done to compare the statistical significance of the results from both instruments. Additionally, a Bland-Altman plot was done for an additional comparison.
Results: :
Twenty three subjects were capable of providing valid data on both instruments; the results are based on 46 data points. The overall mean MPOD for the cohort was 0.341±0.149 for the MacuScope and 0.317±0.191 for the QuantifEye. There was no significant difference between the mean MPOD readings of the two instruments. The mean standard deviation (SD) of each subject’s MPOD readings was 0.107 for the MacuScope and 0.058 for the QuantifEye. There is a significant difference between the two instruments (p<0.0006) when considering individual subject variability.
Conclusions: :
If MPOD is being monitored clinically to assess risk of AMD with the possibility of causing altered treatment regimens, the need for reliable data measurements is imperative. Based on this limited study, both instruments appear to demonstrate reliability based on the means and differences between the means. However, when critically looking at each subject’s data points, there is significant variability between the instruments. Thus, the clinician must take this into account if using MPOD as an indicator for AMD risk and/or clinical care.
Keywords: age-related macular degeneration • macular pigment • clinical (human) or epidemiologic studies: systems/equipment/techniques