Page 14 - Clinical Manual of Small Animal Endosurgery

2 Clinical Manual of Small Animal Endosurgery

instruments) are used for many different diagnostic and therapeutic
procedures.

The rigid endoscope

Rigid endoscopes (also referred to as telescopes) are hollow tubes able
to direct light into a body area or cavity by way of a fibre-optic bundle
and to return the image via a series of lenses. In conventional telescopes,
a central glass lens chain is embedded in an air medium, whereas most
recent telescopes use the Hopkins rod lens technology (Fig. 1.1), in which
the glass lenses have been replaced with glass rods, and air acts as a
negative lens. This system transmits more light, produces better magni-
fication and allows a better field of view in terms of both depth of focus
and the width of the angle of view.
Telescopes are available in a wide range of diameters, ranging from
1.2 to 10 mm. Larger scopes provide more light transmission, superior
image resolution and a larger field of view. Smaller scopes need to be
positioned close to the target area to transmit a clear view, but as they
are used for procedures in smaller areas such as joints or nasal cavities
this is rarely a problem. Larger-diameter endoscopes are preferred for
procedures involving a larger animal, and to obtain panoramic views of
large body cavities.
As no single size of telescope is suitable for all procedures in all
patients, endoscopes are purchased according to the procedures most
commonly performed. A 5 mm telescope is usually adequate for lapar-
oscopy and thoracoscopy in most small animal patients, whereas for
other purposes such as arthroscopy, cystoscopy and rhinoscopy a 2.7 mm
telescope (or smaller) is preferable. Smaller telescopes (4 mm or less) are
very fragile, and consequently a protective sheath is recommended to
avoid damage. The outer sheath (Fig. 1.2) usually has also attachments
for influx and efflux of fluids, and sometimes an instrument channel for
a small flexible biopsy instrument. This determines an increase in the
overall diameter of approximately 1–1.5 mm (for instance a 2.7 mm
telescope with its associated sheath approaches 4–4.5 mm in width),
which has to be considered in scope choice.

Hopkins rod lens telescope

Fig. 1.1 Line drawing of the internal structure of a Hopkins (rod lens)
telescope. The arrangement of rod lenses improves light transmission and
offers a wider field of view compared to a conventional telescope.