Prolapse of the globe is an acute displacement of the globe from the orbit, beyond the plane of the eyelids. This may occur as a result of impact or trauma to the head resulting from dog fights or motor vehicles (see Figure 17.2). Brachycephalic breeds are more susceptible due to shallow orbits and exophthalmus, and as such, more minor trauma or even restraint of the animal can result in proptosis. The amount of damage to the eye will be related to the severity of the trauma; therefore brachycephalic breeds that are more prone to proptosis due to minor trauma may have a more favourable prognosis.
On initial presentation it is important to prevent the eye from drying out. The globe should be lavaged with sterile lactated Ringer’s solution, and a topical sterile lubricant applied frequently while the animal is assessed and stabilised. Eyes that have ruptured, or have avulsed most of the extraocular muscles, should be enucleated once the patient is stable. Eyes that may still be viable should be replaced in the orbit under general anaesthetic, and the eyelids sutured closed temporarily (temporary tarsorrhaphy) to protect the cornea and prevent recurrence of prolapse (see Practical techniques at the end of the chapter). A small space is left at the medial canthus to allow topical medications to be applied. The sutures are usually left in place for 14–21 days.
Ocular haemorrhage in the anterior chamber (hyphaema) is commonly seen as a result of trauma. If no other signs of trauma are evident, then systemic causes of spontaneous haemorrhage (bleeding disorders, hypertension and vasculitis) should be ruled out to make sure there is no underlying life-threatening condition.
Clinical signs of corneal laceration will be similar to those seen with ulceration, including epiphora and blepharospasm. The laceration itself will often be oedematous at its edges, causing the cornea to become opaque in these areas. Lacerations can occur from tooth or claw wounds, or from foreign bodies (see Figure 17.3). The laceration may be superficial, or in some instances the laceration will be deep enough to perforate the eye.
The aim of treatment is to prevent infection, and to protect and support the wound. Topical antibiotic drops are applied to the eye. If there is perforation then systemic antibiotics are usually administered. Wounds that are large or deep should be sutured; simple interrupted sutures of 7/0 or 9/0 Vicryl are usually used. In some instances a conjunctival pedicle flap (see Practical techniques at the end of the chapter) will also be used to support the wound, and bring in new blood supply and nutrition.
Foreign bodies are sometimes encountered in emergency patients; often these are organic matter, i.e. plant or tree material (thorns, splinters), but glass, metal or other material may be seen.
Animals presenting with sudden onset of severe conjunctivitis should be carefully examined to rule out a foreign body such as a grass seed lodged beneath the eyelids. These can often be removed following the application of topical anaesthetic drops, using a moistened cotton wool bud. Sometimes linear abrasions will be seen on the cornea where the foreign body has abraded the surface as the animal blinks.
Penetrating Corneal Foreign Bodies
Smaller foreign bodies may embed themselves within the cornea; these are often splinters, or sometimes fragments of cat’s claw. If they cannot be dislodged by gentle irrigation, then sedation or anaesthesia is often needed to remove these foreign bodies. A 25-G hypodermic needle is useful to dislodge the material, taking care not to push it any deeper (see Figure 17.4).
Perforating Corneal Foreign Bodies
Foreign bodies will occasionally travel through the cornea to become intraocular. The wound will have the appearance of a puncture, and the foreign body may be visible in the anterior chamber. Aqueous humour may be seen leaking from the cornea, and fibrin may be evident within the anterior chamber. These may necessitate surgery to remove them. This decision whether to operate is based on the time elapsed, concurrent damage to the eye and the likely composition of the foreign body (see Figure 17.5).
A corneal ulcer is a break or hole in the corneal epithelium. Ulcers are classified according to their depth: superficial or deep. If ulcers become sufficiently deep, Desçemet’s membrane (the inner most layer of the cornea) may protrude through the ulcer and form what is known as a descemetocoele. Descemetocoeles are at imminent risk of corneal perforation, with leakage of aqueous humour and collapse of the anterior chamber.
Common causes of corneal ulceration include:
- Foreign bodies
- Eyelid disorders
- Keratoconjunctivitis sicca (KCS)
- Infection (melting ulcers)
- Chemical burns.
The animal’s head should be handled gently, as rough handling and pressure applied to the eyes can lead to the risk of rupturing a deep ulcer.
A Schirmer tear test should be carried out to make sure that reduced tear production from KCS is not the cause. Ulcers are usually diagnosed based on the uptake of fluorescein dye during examination of the eye (see Figures 17.6 and 17.7).
If a chemical burn is suspected as the cause of damage to the cornea, then copious lavage needs to be carried out to flush out the caustic agent and prevent further damage. Sterile lactated Ringer’s solution (Hartmann’s solution) should be used. The fluid bag can be connected to a giving set in the usual manner, and the fluid directed from the end of the giving set onto the cornea and conjunctiva. Lavage should be performed for 30 minutes.
Treatment of ulcers includes topical application of antibiotic drops 4–6 times a day. Atropine drops help to reduce pain from the ulcer. A useful addition in deep infected (melting) ulcers is the use of an anticollagenase (some bacteria, especially Pseudomonas and Streptococcus, release an enzyme, collagenase, that destroys the collagen of the cornea) to reduce the damage done by bacteria. This can be acetylcysteine, or the animal’s own plasma can be used. To prepare plasma drops, blood is collected from the patient into EDTA blood tubes and centrifuged to separate off the plasma. This can then be harvested with a pipette and stored in a sterile dropper bottle, in a refrigerator. Anticollagenases need to be applied every 20 minutes to 1 hour initially.
Deep ulcers, descemetocoeles and perforated ulcers require surgery to allow healing to progress. Suturing a conjunctival pedicle graft on to the affected area provides physical support and protection. As the pedicle is living tissue, it provides a source of fibroblasts to help seal the defect, and a blood supply, which helps with the delivery of anticollagenases and antibiotics (see Practical techniques at the end of the chapter).
Anterior uveitis is inflammation of the iris and ciliary body. Uveitis may occur as a manifestation of a systemic disease, or as a result of processes confined to that eye: trauma, corneal ulcers and lens leakage or rupture.
Diagnosis is based on clinical signs. The signs vary depending on the stage of the process or its severity. Pain is present and causes blepharospasm, photophobia and lacrimation. The eye appears red due to circumlimbal vascular congestion. Ciliary spasm leads to a miotic pupil, and the iris appears swollen and dull. Inflammatory cells and exudate, or blood, may be seen in the anterior chamber.
Any primary systemic problems should be addressed, otherwise treatment is symptomatic, consisting of mydriatics to dilate the pupil and anti-inflammatories.
Atropine causes pupil dilation, reducing iris–lens contact and minimising the risk of adhesions forming. Pain from ciliary muscle spasm is also reduced. Atropine is much less effective in an inflamed eye and should be given frequently initially to effect, aiming for a reasonably dilated pupil.
Topical steroids such as dexamethasone or prednisolone should be used intensively (e.g. every 2–4 hours initially). In severe cases, oral prednisolone or non-steroidal anti-inflammatory drugs (NSAIDs) may be used.
Glaucoma occurs when the pressure within the globe (IOP) rises above normal. This increase in pressure leads to degeneration of the optic nerve and damaged vision. The patient may present with acute glaucoma, where the increase in pressure is very recent, or with chronic glaucoma, where the problem has been present longer.
The aqueous humour in the anterior chamber of the eye is constantly being produced and drained. If the drainage fails, the production continues and the increase in volume of aqueous humour causes an increase in pressure within the eye (see Figure 17.8).