Digital image analysis of choroidal hypoperfusion in indocyanine green angiography using a choroid to disc gray-scale ratio.

Purpose: To investigate hypoperfusion of the choroidal circulation in the macula, the brightness of the diffuse fluorescence of indocyanine green (ICG) angiogram (IA) was measured and the ratio of brightness of the macula to that of the disc was used for comparison of choroidal perfusion between different angiograms.

Methods: Ten eyes of 10 young volunteers under 30 years of age (17-28 years old, average 24.7 years old), 10 eyes of 10 old volunteers over 60 years old (60-78 years old, average 66.7 years old) and 5 eyes of 5 patients with age-related macular degeneration (AMD) were examined by IA. The angiograms at 4 and 16 seconds after dye filling were used to measure the brightness of diffuse fluorescence at the macula and the disc on ICG angiograms with a 256-grade gray scale using the Topcon IMAGEnet computer system. The ratio (ch/d ratio) of the averaged brightness of the macula to that of the disc was calculated for each angiogram.

Results: The ch/d ratios of the angiograms 4 seconds after dye filling were 1.41 in the young volunteers, 1.23 in the old volunteers and 0.52 in the AMD patients. The ch/d ratios of the angiograms 16 seconds after dye filling were 0.92 in the young volunteers, 1.02 in the old volunteers and 0.80 in AMD. There were significant differences in the ch/d ratios among the 3 groups 4 seconds after dye filling (p=0.007, Kruskal-Wallis H test,) but there were no significant differences 16 seconds after dye filling (p=0.310).

Conclusion: The ch/d ratio is an adjunctive method for detecting choroidal hypoperfusion in IA, and may be helpful for objective evaluation of the choroidal circulation in chorioretinal diseases.