Page 15 - Clinical Manual of Small Animal Endosurgery

Rigid Endoscopy 3

Fig. 1.2 An operating sheath for a 2.7 mm cystoscope. It is equipped with
two Luer lock stopcocks for fluid infusion and drainage, and a working
channel. A pair of biopsy forceps are located in the channel.

30° angle
of view

2.7 mm
80° field diameter
of view

Fig. 1.3 Line drawing illustrating the effect of rotation on the field of
view of an angled scope.

Other important considerations in choosing a telescope are length and
angle of view. Wider endoscopes are usually longer than narrow ones,
with the 5 and 10 mm-diameter scopes typically having a working length
of 30 or 35 cm, whereas a 1.9 mm scope is only about 10 cm in length.
The most common length of the 2.7 mm scope is 18 cm. Due to the
increased length of the lever arm, longer telescopes can be difficult to
manoeuvre in limited spaces. If a sheath is required (e.g. for cystoscopy),
the length of the sheath must be matched to the scope.
The viewing angle of the telescope affects its orientation and visualisa-
tion of the operative field. The 0° or forward-viewing scope provides the
simplest orientation, as the visual field is in line with the true field.
However, this field of view is the most limited. An angled scope enables
the surgeon to widen the field of view simply by rotation of the longitu-
dinal axis, which allows better examination of relatively inaccessible
areas (Fig. 1.3). However, angled-view scopes are less intuitive to use,