Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

Figure 1.9 Application of topical local anaesthetic to the eye. The hand holding the drops is steadied by resting it on the animal’s head.

Figure 1.10 The blunt (handle) end of a disposable scalpel blade can be used to obtain a corneal scrape.

Figure 1.11(a,b) Tonometry using a Schiøtz tonometer in a dog (a) and a TonoPen® in a horse

(b).

Record keeping (Figure 1.7, p. 12)

•Accurate recording (using simple line drawings as part of the clinical record or employing a standard ophthalmic examination form)

•Photography

SECTION 2

O P H T H A L M I C E M E R G E N C I E S A N D T R A U M A

OPHTHALMIC EMERGENCIES AND TRAUMA

INTRODUCTION

An emergency is an unexpected event requiring immediate action. In all the examples listed below in Box 2.1, prompt and correct action will offer the best chance of full recovery at least cost to the client. The severity of the situation must be assessed as accurately as possible at the first examination, otherwise the best opportunity to restore normality is lost. Management options include referral to a specialist veterinary ophthalmologist if the facilities of the practice are inadequate or the expertise of the staff is insufficient to cope with the problem.

Box 2.1 Ophthalmic emergencies

•Acute exophthalmos including globe prolapse (globe prolapse commonest in dog)

•Orbital inflammation – abscess and cellulitis (all species, but commonest in dog)

•Foreign bodies (all species)

•Gross trauma to globe and/or adnexa (all species)

•Complicated corneal ulceration and corneal infection (all species)

•Thermal and chemical injuries (all species)

•Acute uveitis (mainly dog and horse)

•Acute glaucoma (mainly dog, but other species can be affected)

•Sudden loss of vision (all species)

•Sudden onset of ocular pain (all species)

There are some general rules that are common to all species, of which meticulous examination of the eyes and the rest of the animal is the most important, followed by the ability to decide, at an early stage, the most appropriate course of action, including prioritisation of the clinical findings (Figure 2.1(a,b)). Sedation and local nerve blocks are helpful in the assessment of large-animal ocular emergencies and, sometimes, examination under general anaesthesia will be required at an early stage of assessment in all species. Topical local anaesthesia may be a useful adjunct to ocular examination and may also be used to reduce the amount of general anaesthetic required in patients under general anaesthesia, but it should not be used as part of any treatment regime. Systemic analgesia is helpful for both the examination and subsequent management of many ophthalmic emergencies. Indwelling lavage devices will make treatment of large animals with painful eyes very much easier and, certainly, more precise. For periocular and ocular insults in herbivores, and for some deep penetrating injuries in carnivores, prophylactic tetanus treatment should be administered.

When intraocular surgery is required it is assumed that it will be performed under general anaesthesia and a brief resumé of routine general anaesthesia is outlined in Appendix 3. For extraocular and adnexal surgery the anaesthetic techniques that may be selected are mentioned briefly in the text. Similar considerations apply to surgical procedures outlined in other sections of the book.

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

Figure 2.1(a,b) Gross appearance (a) and section (b) of a ruptured globe (with acknowledgements to J.R.B. Mould).

ACUTE EXOPHTHALMOS (PROPTOSIS)

The differential diagnosis of acute exophthalmos or proptosis (forward displacement of the globe) is not always easy, as the location of the underlying abnormality can be periorbital, orbital or a combination of both and, on occasion, there may also be globe involvement. Causes include trauma, periorbital and orbital infection, inflammation, abscessation and haemorrhage. Rarely, aggressive tumour growth with neoplastic infiltration can also present acutely. The commonest causes of orbital neoplasia are outlined later.

TRAUMATIC GLOBE PROPTOSIS AND PROLAPSE

Traumatic globe proptosis and globe prolapse (dislocation of the globe beyond the plane of the eyelids) are usually the result of direct impact to the eye, orbit or periorbita, but can also be associated with head and neck injuries. Adnexal, subconjunctival and orbital haemorrhage are common accompaniments; the latter may dissect anteriorly beneath the conjunctiva.

Acute proptosis

In cases of acute proptosis, provided that the globe is retained within the orbit and within the plane of the eyelids, treatment is conservative and consists of ocular lubrication to protect the cornea, systemic analgesics and restricted activity. Early application to the periocular region of an ice pack wrapped in a towel may help to reduce periocular swelling. Emergency tarsorrhaphy (suturing the upper and lower eyelids together) to provide effective tamponade is sometimes needed if progressive proptosis occurs as a result of, for example, continuing retrobulbar haemorrhage. Possible complications of extensive haemorrhage include an increase of intraocular pressure (IOP) and optic nerve compression because of the high intraorbital pressure.

Globe prolapse (Figure 2.2(a,b))

Globe prolapse is commoner in dogs than other species and in commoner brachycephalic dogs with a shallow orbit. It may sometimes occur if the animal is not handled

properly, especially if the dog is manipulated by the scruff of the neck. The Persian cat is unusual amongst cat breeds in having a relatively shallow orbit. Globe prolapse is rarer and more serious in non-brachycephalic dogs and other species because more force will be required to dislocate the globe from a deeper orbit. The prognosis for normal vision in the long term is always guarded because traction damage to the optic nerve often results in Wallerian degeneration and eventual optic atrophy. Fewer than 50% of dogs retain vision in the long term and in cats almost 100% will be left with a blind eye. Avulsion of extraocular muscles (especially the medial rectus muscle) and nerve damage are common, so the animal is sometimes left with a squint.

Figure 2.2(a,b) Globe prolapse of the right eye in a Pekingese following direct trauma to the head from a kick. The zygoma was also fractured. The clinical presentation of this ‘red eye’ is a combination of subconjunctival haemorrhage and venous congestion – the latter because the eyelids have gone into spasm behind the globe equator, resulting in impeded venous return (a). Following restoration of the prolapsed globe to the orbit, the lateral canthotomy was closed and the upper and lower eyelids were sutured together (b). Three horizontal mattress sutures of 4-0 silk were laid, with vertical entry through the lower eyelid skin, via the lower and upper eyelid margins and upper eyelid skin, horizontally through hollow silastic tubes and then vertically back to emerge from the lower eyelid skin. The sutures do not penetrate the full thickness of the eyelids. The position of all the sutures should be checked before they are tied, incorporating additional horizontal hollow silastic tubes for each lower eyelid suture. The aim of the temporary tarsorrhaphy is to provide good ocular surface protection whilst ensuring that that the suture tension is spread so that there is no possibility of inadvertent abrasion to the underlying cornea.

Diagnosis of globe prolapse

•This is straightforward and can usually be made from the owner’s description

•History may be helpful (e.g. road traffic accidents and fighting) or unhelpful (e.g. genuinely unknown and non-accidental injury)

•Check for and prioritise any other injuries present (i.e. may need to stabilise the patient before attending to the eye)

•Assessment of potential ocular damage (e.g. globe rupture) can be aided by ultrasonography

Treatment

•Speed is of the essence, so the animal should be seen immediately. The owner may be able to prevent further damage, notably corneal and conjunctival desiccation, by

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

gently applying pressure to the region with soft material such as a clean tea towel or cotton handkerchief that has been soaked in water. This action sometimes restores the globe to the orbit in brachycephalic dogs, but the owner should still seek rapid veterinary attention.

•Very soon after prolapse has occurred the eyelids go into spasm behind the equator of the globe making reduction more difficult and adding to the oedema and marked vascular congestion (redness) which are a rapid consequence of this problem (Figure 2.2(a)). Once this situation is reached it may be impossible to reposition the globe without general anaesthesia.

•Provided other injuries permit, and the optic nerve remains intact, general anaesthesia is performed without delay. Following application of ophthalmic ointment with an oily excipient (e.g. fucidic acid gel or chloramphenicol ointment), the eye is repositioned by gently easing the eyelids over the globe (not by simply attempting to force the eye back into the orbit). It is often sensible to perform a generous lateral canthotomy before attempting this manoeuvre if swelling is marked. If the globe has been completely dislocated from the orbit and the optic nerve avulsed, then it is better to remove the globe.

•Once the eye is back in the orbit it should be retained in place by temporary tarsorrhaphy (Figure 2.2(b)). The upper and lower lids are sewn together using approximately three horizontal mattress sutures of non-absorbable soft material such as 3-0 to 4-0 silk. These are preplaced so as to avoid contact between the sutures and the globe. Stents, made from, for example, silastic tubing are used to support the horizontal passage of the sutures as they are often under considerable tension. If a lateral canthotomy has been performed it is closed after the tarsorrhaphy has been completed.

•If there are no contraindications, the patient is usually given a single dose of corticosteroid (e.g. dexamethasone) at the time of surgery and a 7–10 day course of systemic antibiotic. The sutures are removed (following topical local anaesthesia) after 14 days. A lateral squint (because of avulsion of the medial rectus muscle) may be obvious at the time of the prolapse, but is more likely to be observed when the tarsorrhaphy is taken down.

ORBITAL INFLAMMATION

The origins of orbital cellulitis and orbital abscess may be identical, and both can be a cause of proptosis. Orbital cellulitis is typified by diffuse inflammation, whereas a retrobulbar abscess (orbital abscess) is characterised by localised inflammation. Other less common causes of orbital inflammation include acute inflammation of the lacrimal (dacryoadenitis) or zygomatic gland (sialoadenitis), acute masticatory myositis and acute extraocular polymyositis, all of which can present as acute exophthalmos. Dacryoadenitis and sialoadenitis may be associated with infection, in which case a course of systemic antibiotic is indicated. Anti-inflammatory therapy may also be required if the inflammation fails to respond to antibiotics. For acute masticatory myositis and acute extraocular polymyositis, immunosuppressive levels of systemic corticosteroids (prednisolone 2mg/kg) are indicated initially and then slowly tapered off if there is a positive response.

RETROBULBAR (ORBITAL) ABSCESS

Clinical signs (Figure 2.3)

•Not uncommon; affected animals usually present with unexplained acute onset of ocular discomfort and they may be pyrexic

•A history of previous trauma, including fights and stick injuries, is helpful, but may be separated from the acute onset of clinical signs by days or weeks. Infections of the nose, mouth or sinuses also have the potential to involve the orbit

•Affected animals are often very reluctant to eat and there is invariably severe pain on attempting to open the mouth

•There is often marked conjunctival injection and a mucopurulent ocular discharge. Conjunctival oedema (chemosis) may also be present

•Exophthalmos, which is generally, but not invariably, axial (i.e. there is no associated squint). Ocular motility is usually restricted because of the space-occupying effect of the inflammation

•The third eyelid is prominent

OPHTHALMIC EMERGENCIES AND TRAUMA