A Ophthalmic Surgery

Some of the conditions of the eye which are amenable to surgery we covered in the First Aid lectures, i.e. eyeball prolapse and acute damage to the cornea. I shall cover them again, so you won’t have to look it up.

1) Prolapsed eyeball
An acute injury found usually in brachycephalics with very shallow orbits or in severe RTA’s. Speed is the key to saving a prolapsed eye, 30 minutes maximum to replace. Surgical intervention may involve a lateral canthotomy in which the lateral canthus is cut to provide more room to replace the eye. After replacement, the lids are usually sutured shut (tarsoraphy) to keep the eye in place until the swelling has subsided. (5-7 days).

2) Enucleation
Removal of the eyeball. (In some cancers of the eye it is necessary to remove the eye plus all associated muscles and other structures inside the orbit. This is called evisceration.).
Because the eye is to be removed, a full surgical prep can be carried out. The eyelids are then usually sutured shut and the eye is removed by dissection around the outside of the globe itself, removing the eye intact. There are prostheses available but it is unusual to use them. The problem with enucleation is surgical dead space in which blood can accumulate. This is usually eliminated by suturing a pad over the wound and pressing into the socket.

3) Entropion and ectropion
These are inherited diseases. In ectropion the eyelid turns out. In entropion the eyelid turns in . Both diseases cause corneal damage. Some dogs have a combination (“Diamond eyes” in the St. Bernard, for instance). Surgical correction of ectropion is performed by removing a wedge of lid, and so tightening it up. (There are alternative methods). Surgery for entropion is usually done by removing an ellipse of tissue from next to and parallel to the eyelid. Stitching the defect together then pulls the lid outwards.

4) Corneal damage
Corneal damage gives rise to ulceration which can be deep enough to threaten the eye. There are various procedures to protect the cornea and stimulate healing.
-Contact Lenses, widely available but expensive
-Third eyelid flap. The nictitating membrane is drawn across the damaged eye surface and sutured up in the opposite corner of the orbit. This then act like a bandage. The disadvantage of this technique is that the eye is invisible and so progress cannot be measured. It is has more generally been replaced with:
-Conjunctival graft / flap. A piece of conjunctiva is dissected out and sutured across the damaged area of cornea. I is left attached by a strip of conjunctiva to its origin. When the damage is healed, the strip is cut and the graft dies off. The advantage is the eye is visible throughout.

General surgical principles around the eye
Always protect the eye from iatrogenic damage (damage caused by the treatment!). Clip carefully or use adhesive disposable drape. Use Povidone iodine prep. if possible very dilute hibiscrub is acceptable.. Apply suitable ointment to the surface of the eye just in case. If the eye is contaminated accidentally, flush with plenty of saline.

B Circulatory Surgery

1) Portosystemic shunts
These shunts arise in the young animal when a by-pass vessel which functions in the embryo fails to close after birth. The vessel runs from the hepatic portal system (porto-...) to the posterior vena cava (....-caval) and shunts blood rich in the products of digestion directly into circulation, by-passing the liver. Unfortunately, some of these are toxic (they would have been cleared by liver metabolism), and cause significant problems, particularly in the brain. Some of these shunts can be closed off surgically, particularly if they are located outside the liver (usually small breeds). Others are difficult to close as they are inside the liver tissue.

2) Patent ductus arteriosus
Another by-pass vessel which fails to close, this time between aorta and pulmonary artery. In the foetus it by-passes the lungs, but should close at birth. The pressure in the aorta after birth causes the lungs to over-circulate as blood goes down the PDA. Most PDA’s can be tied off in the chest. Some are too large or fragile for surgery.

3) Pulmonic stenosis
The pulmonary artery is sometimes congenitally narrow where it emerges from the heart, causing the heart to work too hard pumping blood around the lungs. This narrowing can be corrected in some cases using instruments inserted into the vessel. This is a specialist procedure!

Hernias and Ruptures

A hernia is passage of organ(s) or tissue through an opening which potentially or already exists as a result of normal anatomy and development. These openings are lines of weakness or areas which fail to close over during development.
Some hernias:
- Umbilical
- Inguinal (through the inguinal canal. Seen usually in bitches as in males the testicular / spermatic vessels occupy this region.
- Tentorial. Seen in hydrocephalus, when pressure in the brain forces it back out of the skull.
- Pericardioperitoneal. The diaphragm fails to develop properly and the abdomen communicates with the pericardial sac.

Hernias are generally classified as:
Reducible- the herniated structures can be replaced by manipulation back in their normal position.
Irreducible- the hernia is permanent and cannot be reduced.
Strangulated - the structures within the hernia have twisted so that the blood supply is cut off into the hernia. This can be very dangerous if, for instance bowel inside an umbilical hernia becomes strangulated.

A rupture is effectively a traumatic hernia. Damage to a tissue or an organ allows herniation of other tissues or organs through the defect.
Some examples:
- Diaphragmatic rupture after an RTA
- ventral abdominal rupture, when muscle is traumatically detached from the pelvis
- Perineal rupture. Usually due to an enlarged prostate and straining.

Surgery is usually necessary to repair ruptures. Hernias may be regarded as benign if small, particularly if only fat has herniated through the opening, and may be left.

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