An endoscope is an instrument which consists of a tube of fibre optic fibres contained in a waterproof membrane. A light source is connected to the endoscope and transmits light down the fibres and back to an eye piece, allowing the operator to look at the region adjacent to the end of the endoscope. An endoscope can be used to look at remote body systems.
Flexible endoscopes are commonly used to assess the function of the larynx and pharynx, to investigate nose bleeds and nasal discharges and to diagnose a variety of lower airway conditions. They can also be directed into the stomach to look for gastric ulcers, gastroscopy.
The flexible endoscope is placed up the nostril of the horse and navigated through the nasal passages to the point of interest. Most horses find the initial placement of the endoscope uncomfortable and may cough, but usually settle once the nasal passages are past, some will require sedation. The endoscope can be attached to a television monitor to allow the area under investigation to be easily visualised. If a lower respiratory problem is suspected samples may be taken trans-endoscopically. In some cases the larynx and pharynx may look normal at rest, but a problem at exercise may be suspected. These horses can be referred for dynamic endoscopy, when a flexible endoscope is attached to the horse's bridle and the horse is ridden. Video recordings are made to enable assessment of laryngeal function at exercise.
Rigid endoscopes work under the same principle, but are introduced into the body via incisions made by a surgeon. They can be used to investigate joints and tendon sheaths, arthroscopy or the abdomen, laprascopy. The horse to be examined will be placed under general anaesthetic or in some cases under very heaving standing sedation. The rigid endoscope can also be used to guide instruments, introduced via separate incisions to perform 'keyhole' surgery.