Retinal nerve fiber layer retardation measurements using a polarization-sensitive fundus camera.

To measure the retardation distribution of the optic retinal nerve fiber layer (RNFL) from a single image, we have developed a new polarization analysis system that is able to detect the Stokes vector using a fundus camera. The polarization analysis system is constructed with a CCD area image sensor, a linear polarizing plate, a microphase plate array, and a circularly polarized light illumination unit. In this system, the Stokes vector expressing the whole state of polarization is detected, and the influence of the background scattering in the retina and of the retardation caused by the cornea are numerically eliminated. The measurement method is based on the hypothesis that the retardation process of the eye optics can be quantified by a numerical equation that consists of a retardation matrix of all the polarization components. We show the method and the measurement results for normal eyes. Our results indicate that the present method may provide a useful means for the evaluation of retardation distribution of the RNFL.

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.

Analysis of choriocapillaris flow patterns by continuous laser-targeted angiography in monkeys.

PURPOSE: To investigate choriocapillaris flow patterns and its segmental distribution in monkeys by continuous laser-targeted angiography (LTA). METHODS: A slit lamp was modified to incorporate two kinds of lasers (argon and diode). Carboxyfluorescein (CF) was encapsulated in heat-sensitive liposomes and injected intravenously. Encapsulated CF was released locally by applying a continuous heat beam provided by the diode laser (810 nm). Video angiograms were generated with excitation illumination provided by the argon laser (488 and 514 nm), to observe selective images of the choriocapillaris. RESULTS: Continuous application of the diode laser disclosed three distinct phases (filling, plateau, and draining) of fluorescent images of the choriocapillaris. In the plateau phase, a cluster of lobules fed by a common arteriole was uniformly illuminated. This defined area did not change in size while a continuous diode laser was applied to the same spot. Only in posterior regions did the angiograms demonstrate that during the filling and draining phases each lobule was filled from a central spot and drained along a peripheral ring, showing honeycomb flow patterns. In peripheral regions, large choroidal vessels as well as choriocapillaris were observed. CONCLUSIONS: Continuous LTA demonstrated clusters of lobules fed by a common arteriole, and each cluster was found to be functionally independent. There were regional differences in choriocapillaris flow patterns, which suggests that the choriocapillaris provides a more highly efficient system of outflow in posterior regions than in peripheral regions. This modified LTA method appears to be useful in analyzing choroidal circulation in vivo.