Summary
cw-Nd: YAG laser radiation was effective in producing blood flow stasis within arteries
(35 – 40 μm in diameter) of pigmented rabbit mesentery (beam spot size: 80 μm; fluence
:2 × 104 J cm−2) and choroid (beam spot size : 200 μm; fluence: 6 × 102 J cm−2) However, the mechanism by which this was achieved differed in each case, and depended
upon the energy absorbing structures present in the irradiated tissue. In non-pigmented
tissue, such as the mesentaty, haemoglobin represents the primary absorption centre,
and the temperature attained within the vessel lumen (as inferred from morphological
changes) is sufficient to denature plasma proteins, in particular fibrinogen, which
consequently occlude the vessel lumen and arrest bleeding. In pigmented tissue, such
as the choroid, melanocyte granules represent the primary absorption centre, which
is thus shifted from the vessel lumen to the stroma. The temperature rise achieved
within the vessel lumen is consequently loweq as evidenced by the absence of plasma
protein denaturation. Blood flow stasis nonetheless occurs, but is triggered according
to the normal haemostatic mechanism.
