Page 1162 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Eyes 1137

VetBooks.ir 11.21 11.22

Fig. 11.21 Cell collection for culture and sensitivity.
A sterile culturette can be used to swab the cornea for 11.23
microbes. Care should be taken to avoid inadvertent
contamination from the eyelids, and samples are
ideally collected prior to use of topical anaesthetics in
order to maximise yield.

Corneal/conjunctival cytology
Samples for cytology may be collected following the
application of a topical anaesthetic. A Dacron swab,
cytobrush, stainless steel spatula (e.g. Kimura spat-
ula) or the blunt end of a scalpel may be used to collect Figs. 11.22, 11.23 Retrograde flushing of the
scrapings for cytological evaluation. Fungal organ- nasolacrimal system. (11.22) The distal opening is on
isms have an affinity for Descemet’s membrane and the floor of the nasal vestibule. After administration of
the deeper layers of the corneal stroma; therefore, an anaesthetic gel over the distal duct, the opening can
when collecting material for evaluation of corneal be cannulated with a variety of catheters, such as the
ulcers or abscesses, deep scrapings from the centre of 5-Fr feeding tube shown (11.23).
the lesion as well as from the periphery are required.
These samples are placed on microscope slides and
Gram or Wright–Giemsa stains are routinely used or lower punctum may be cannulated with a small
to evaluate the types of cells and organisms present. urinary catheter, or an intravenous catheter with the
More specialised stains such as periodic acid–Schiff stylet removed, and flushed with 20–30 ml of physio-
(PAS) stain and Gomori’s methenamine silver stain logical saline in an anterograde fashion (Fig. 11.24).
may be used when fungal infection is suspected. The addition of a small amount of fluorescein dye
will facilitate identification of the fluid as it exits the
Nasolacrimal system cannulation and lavage nasal or lacrimal punctum. Any debris flushed from
If an obstruction or abnormality in the nasolacrimal the NLS should be collected for cytology as well as
system (NLS) is suspected, a nasolacrimal flush may for culture and sensitivity testing.
be performed. The NLS is normally easily cath-
eterised and flushed in a retrograde manner with Anterior and posterior chamber paracentesis
20–60 ml of physiological saline, using a soft 5- or Anterior chamber paracentesis (aqueocentesis) and
6-Fr feeding tube, tom-cat catheter or polyethylene posterior chamber paracentesis (vitreocentesis) are
tubing (Figs. 11.22, 11.23). Alternatively, the upper very rarely indicated but may be performed in the