The effect of transmission bandwidth on the quality of ophthalmological still and video images

We have examined the minimum realtime transmission speed for video-angiogra phy with the Rodenstock scanning laser ophthalmoscope (SLO) with respect to spatial and contrast resolution. An SLO fluorescein video-angiography sequ ence was recorded using high-quality media and relayed to a remote site at transmission speeds ranging from T3 (4.5 Mbit/s) to 0.125T (197 kbit/s). Im ages were compared with each other subjectively by an ophthalmologist and o bjectively with image processing software. When compared qualitatively ther e was little difference between the T3 and T1 images. The T1 images scored well on clarity and contrast, while 0.5 T was satisfactory but inferior to T1. Transmission speeds below 0.5 T were inadequate. The digital analysis s howed a slight difference between T3 and T1. We calculated that there was u p to a 92% loss of resolution at 0.25T and up to a 98% loss at 0.125T. Base d on our quantitative and qualitative analysis, a T3 line provided the high est bandwidth and best resolution, as expected. However, 0.5 T gave satisfa ctory results for realtime consultations and appears to be the minimum spee d required for ophthalmic purposes, producing few motion artefacts and good resolution.