Ординатура / Офтальмология / Английские материалы / Notes on Veterinary Ophthalmology_Crispin_2005

OPHTHALMIC EMERGENCIES AND TRAUMA

28 Notes on Veterinary Ophthalmology

minimum) in all species. A combination of cephalexin (effective against aerobic bacteria) and metronidazole (effective against anaerobic bacteria) is normally selected.

•Abscess drainage is an alternative in carnivores, but only if there is obvious redness and a fluctuating swelling or a draining tract behind the last upper molar tooth. The animal is anaesthetised (an analgesic premedicant is sensible) and positioned with a head down tilt. A cuffed endotracheal tube (uncuffed e/t tube in the cat) is passed and the pharynx is packed with damp gauze bandage that can be secured to the endotracheal tube. The abscess is drained immediately posterior to the last upper molar tooth. A small nick is made in the mucous membrane with a scalpel and the actual probing of the region is best done with fine haemostats; sharp instruments should be avoided. Success is indicated when free drainage is established and pus or serosanguinous fluid is released. The material should be subjected to a smear for cytology, as well as culture and sensitivity, so that the correct choice of broadspectrum systemic antibiotic is made. The wound is left open.

ORBITAL CELLULITIS

Orbital cellulitis is, strictly speaking, diffuse inflammation of structures posterior to the orbital septum, and is most commonly caused by infection. Orbital cellulitis is rare, but can be life threatening because of the proximity of the brain and meninges. Any infection involving the nose, mouth or sinuses has the potential to spread to the orbit, but occasionally there is extension from sites such as the pituitary gland (e.g. pituitary abscess) and equine guttural pouch. The most frequently identified causes include puncture wounds of the periorbita and eye, penetrating foreign bodies that migrate from the oral cavity and sinusitis. Actinobacillosis (Actinobacillus lignieresii) is a possible infectious cause in herbivores, cattle particularly.

Clinical signs

•Similar to those of retrobulbar abscess, but the periorbital swelling is more diffuse and there is often marked swelling of the eyelids and conjunctiva. Ocular motility may be restricted if the inflammation surrounds the globe

•The onset is usually sudden and exophthalmos can be a key presenting sign; thirdeyelid prominence is not always present

•Painful and serious

•Pyrexia and anorexia may be present

•Leukocytosis can be marked

Diagnosis

•Diagnostic imaging can be helpful

•Needle aspiration or biopsy is required to provide material for culture and cytology or histology

Treatment of orbital cellulitis

•Any wound should be thoroughly cleaned and debrided; more radical excision may be required if there is a deep penetrating injury or tissue necrosis

•Hot compresses can be helpful

•A course of systemic antibiotic should be given as outlined above for a retrobulbar abscess and, ideally, selected on the basis of culture and sensitivity testing

•Exposed cornea and conjunctiva require protection with a bland ophthalmic lubricant, with or without antibiotic (e.g. chloramphenicol ointment), during the period of globe prominence

•Systemic analgesics will be required for as long as pain persists

•If the cellulitis is a consequence of a deep penetrating injury then prophylactic tetanus treatment should be administered

ORBITAL NEOPLASIA

Orbital neoplasia is an uncommon cause of acute exophthalmos as most types of orbital neoplasia are associated with a chronic time course. There is a wide range of possible tumour types and acute onset exophthalmos is usually associated with highlymalignant and invasive tumours or haemorrhage from such tumours. The origin of primary tumours is likely to be orbital or nasal, the latter invade the orbit via the thin medial orbital wall. Secondary tumours are often multifocal and the orbit is one of a number of sites involved. Multicentric lymphoma is the commonest secondary tumour to involve the orbit and affected horses, in particular, can present acutely. If refined diagnostic imaging techniques are not available, referral should be considered.

Diagnosis and differential diagnosis

•The classical signs of an orbital space-occupying lesion may be present (exophthalmos and third-eyelid prominence)

•In addition there may be some or all of globe deviation, resistance to globe retropulsion, vascular congestion, chemosis, ocular discharge, nasal discharge, reduced airflow from the nostrils, epistaxis and intraoral swelling

•Clinical signs may also be more generalised, particularly if the orbital involvement is indicative of metastatic spread

•Diagnostic imaging techniques (radiography, ultrasonography, computed tomography, magnetic resonance imaging) are key to establishing the location and extent of the tumour

•Accurate diagnosis invariably requires histological examination of biopsy material and allows management options to be defined more precisely

Management

•The prognosis for tumours associated with acute onset exophthalmos is guarded to grave

•The major treatment options are surgical removal, radiotherapy and chemotherapy, with or without sacrifice of the eye. The location and extent of most orbital tumours render the retention of a functional eye most unlikely if surgery is undertaken

•Such cases are best referred

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

FOREIGN BODIES

The majority of foreign bodies are associated with acute onset of ocular pain, blepharospasm and lacrimation. The history can be very helpful and careful examination often reveals the source of discomfort.

Clinical approach

•The history from the owner is usually typical and the onset can sometimes be related to specific events, like the last period of exercise or to factors in the animals’ environment

•Careful examination of the eye, adnexa and periocular region is crucial

•It is usually sensible to examine the eye following topical application of local anaesthetic (e.g. proxymetacaine hydrochloride 0.5%)

•In large animals, systemic sedation/analgesia and an auriculopalpebral (AP) nerve block will aid examination

•In some small animals, and occasionally in large animals, the eye is so painful that general anaesthesia should be selected at the outset

•Diagnostic imaging is an important part of clinical assessment (radiography, ultrasonography and CT scanning)

•Magnetic resonance imaging must not be used if there is any possibility of magnetic foreign material (ferrous metals)

Clinical signs

•Acute discomfort, with excessive lacrimation, blepharospasm ± conjunctival oedema are the most common early clinical signs. If the foreign body is not identified and removed then the discharge may quickly become mucopurulent or haemorrhagic.

•The foreign body may be visible. However, if it is not immediately obvious a thorough examination of all aspects of the conjunctiva should be carried out, looking carefully under the upper and lower eyelids and beneath the third eyelid (see Section 3, pp 101–109 for the technique). The upper and lower puncta should be inspected. The cornea, limbus and ‘white’ of the eye should be examined minutely, followed by the internal ocular structures. Magnification is often required, particularly in, for example, small rodents.

•If no obvious cause is found then referral should be considered, particularly when the history is suggestive of a foreign body. It is not acceptable to adopt a wait and see approach as foreign bodies can migrate to less accessible sites, including within the eye.

INTRAOCULAR AND INTRAORBITAL FOREIGN BODIES

The history may be helpful, but in many cases there is no history and it is the presence of a relatively innocuous wound to the periocular region or globe, or a change of ocular appearance, that prompts further investigation. Some foreign bodies, typically gunshot, will have penetrated and traversed the globe before they become embedded in the orbit. The entry wound in gunshot injuries is not always obvious in hairy animals and any unexplained periocular or ocular wound should prompt further investigation, including diagnostic imaging (e.g. ultrasonography).

Many foreign bodies are relatively inert (glass, high quality plastic, stone and highquality alloys such as stainless steel) whereas others (organic material, low-grade plastic, iron, copper and low-quality alloys) are not well tolerated. Gunshot injuries are common in cats (usually non-accidental injury) and gun dogs (usually accidental injury).

Metallic foreign bodies that have travelled at high speed into the eye or orbit will generate a temperature high enough to sterilise the foreign body so that endophthalmitis is less likely (Figure 2.4(a–c)). In contrast, intraocular or orbital organic material may well provoke endophthalmitis or orbital cellulitis. Organic material may reach the orbit or eye directly (e.g. stake injuries from wood) or following migration from other sites, such as the conjunctival sac (e.g. grass seeds).

(a)

Diagnosis

•History

•The naked-eye appearance is highly variable, ranging from no indication of external damage to complete disruption of the globe

•Comprehensive examination of the periocular region, adnexa and eye

•Diagnostic imaging techniques may include orbital radiography, ultrasound examination and CT scans. MRI may be used to identify non-metallic foreign bodies not identified by the other techniques, but must not be used if there is any chance of the foreign body consisting of magnetic foreign material

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

Management

The assessment and management of these cases requires specialist assistance, unless the eye is beyond repair and painful, in which case it is best removed.

LACRIMAL SYSTEM FOREIGN BODIES

Foreign bodies (FBs) may become lodged in the puncta, canaliculi or nasolacrimal ducts. Investigation is as for lacrimal dysfunction (see later) and should be performed in such a way that the foreign body is not inadvertently flushed into the narrow intraosseous portion of the nasolacrimal duct (Figure 2.5(a,b,c)).

(c)

Figure 2.5(a–c) Foreign body (grass seed) in the upper punctum of a dog. A unilateral profuse mucopurulent ocular discharge is the most striking feature of the clinical presentation (a), but the owner had also reported intermittent haemorrhage. Once the discharge had been carefully cleaned away it was apparent that the haemorrhage was a consequence of the mechanical irritation from a foreign body whose tip can be seen protruding from the upper punctum (b). The grass seed has been removed and the upper punctum and canaliculus cannulated prior to gentle irrigation to remove any remaining small particulate matter via the lower canaliculus and punctum (c).

Treatment

•Visible foreign bodies are grasped with fine forceps and gently extracted from the affected punctum, taking care to ensure that no small particles remain behind. Gentle (retrograde) irrigation usually via the normal, unaffected, punctum with digital

occlusion of the lacrimal sac region (to prevent access to the nasolacrimal duct) may be needed to remove detritus from the affected punctum and canaliculus. This is because the foreign body may undergo some disintegration within the affection punctal and canalicular portions of the lacrimal drainage system.

•There is usually no need to provide antibiotic treatment in the management of acute cases. Where a short course of antibiotic treatment is felt to be necessary it is better to supply a solution rather than an ointment or gel.

•Complex cases, particularly those where the foreign body is not visible, may require specialist help and early referral should be considered.

CONJUNCTIVAL FOREIGN BODIES INCLUDING THOSE

INVOLVING THE THIRD EYELID

Foreign bodies are a reasonably common source of conjunctival injury and are frequently of an organic nature (seeds, barley awns, wood, etc). The conjunctival sac can accommodate surprisingly large foreign bodies, whereas less spectacular, but usually more traumatic, are foreign bodies, sometimes small in size located beneath the third eyelid (Figure 2.6(a,b)). The rapid onset of conjunctival oedema, especially in cats, can make the task of finding foreign bodies more difficult.

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

CORNEAL FOREIGN BODIES

Clinical signs are similar to those for any acute corneal injury (i.e. pain, blepharospasm and lacrimation), with the foreign body being visible in many instances (Figure 2.7(a–c)). Referral should be considered for complex cases (e.g. deep FBs with risk of ocular damage or collapse of the globe on extraction).

(b)

(a)

(c)

Figure 2.7(a–c) Corneal foreign body (thorn) in a dog (a). Note that the thorn is of regular shape and does not penetrate the full thickness of the cornea, so it can be removed safely without fear of additional corneal damage or globe collapse. General anaesthesia is not usually required and the foreign-body in this case was removed using a foreign-body needle (b) as illustrated (c) following the topical application of local anaesthetic.

Treatment

•Foreign bodies require removal if they are causing irritation or are capable of causing irritation. Organic foreign bodies are the commonest necessitating this approach.

•Superficial foreign bodies can be removed a few minutes after application of topical local anaesthetic (e.g. proxymetacaine hydrochloride 0.5%) using a foreign-body spud, a surgical spear, or cotton wool wound round the tips of fine mosquito forceps. Patience is required. Flat foreign bodies in particular (e.g. plant material, flakes of metal or paint) can be quite difficult to remove as they become embedded in the superficial cornea where they set up a considerable reaction.

•Foreign bodies that have penetrated the cornea and are accessible are best removed using a 25-gauge needle or a foreign-body needle, inserted at 90° into the protruding tip of the foreign body. The foreign body is removed slowly and carefully in the

direction exactly the reverse of the angle of entry. Whilst it is tempting to attempt to grasp the foreign body with tissue forceps, this may cause it to penetrate more deeply and is better avoided. It is sometimes necessary to undermine corneal foreign bodies with a 15-gauge scalpel blade or a Beaver blade to facilitate removal.

•Advice or referral should be sought for animals with complex foreign bodies (e.g. fish-hooks), intracorneal foreign bodies, those that may also have penetrated the iris

± lens, and those of uneven shape (e.g. some thorns).

•Corneal foreign bodies and micropuncture wounds in general may become the site of a corneal stromal abscess (see Section 7, p. 289), especially when organic material is involved. Infection (usually by fungi or bacteria) is an additional complicating factor when there has been a puncture wound or foreign body retention. The history and clinical appearance (white, cream or yellow in colour) may help in reaching a diagnosis. Abscesses often show no tendency to heal, particularly if they are deep, and natural resolution will only occur if the foreign material triggers a vascular response. If topical medical treatment does not bring about improvement and resolution of an abscess, then surgical extirpation is probably the treatment of choice.

TRAUMA

Traumatic injury is common in veterinary ophthalmic practice and there are a variety of causes. The clinical approach is as already outlined for foreign bodies. It is also worth noting that the number of cat-related traumatic ocular injuries has increased in dogs and cats in the UK in parallel with the increase in the cat population.

ORBITAL TRAUMA

Trauma in this region, especially that associated with penetrating injury, can result in direct damage to the blood vessels, nerves and muscles of the orbit. Damage to bone is less common.

Clinical signs

•Pain, blepharospasm and lacrimation are common to most acute insults involving the globe and orbit

•Asymmetry of the head, ± eye, and palpable disruption of normal bony contour if a displaced fracture is present

•Strabismus with or without exophthalmos. Enophthalmos in the acute stage is rare and may indicate globe rupture, major orbital disruption or entrapment of extraocular muscles associated with displacement of bony fragments

•Vision may or may not be affected according to such factors as associated intraocular damage (e.g. intraocular haemorrhage, globe rupture) and the type of extraocular damage (e.g. stretching or avulsion of the optic nerve may have an immediate effect on vision). In some cases, however, the eye and vision are normal

•Other possible clinical signs include epistaxis, crepitus and subcutaneous emphysema. The latter usually indicates a fracture involving a paranasal sinus

OPHTHALMIC EMERGENCIES AND TRAUMA

OPHTHALMIC EMERGENCIES AND TRAUMA

Diagnosis

•History and clinical signs

•Careful visual inspection to compare both sides of the head

•Gentle palpation of the orbital and periorbital region

•Ophthalmic examination

•Diagnostic imaging – radiography – at least two views of the skull if fractures are a possibility. Other techniques (e.g. CT and MRI) can be very useful, but will require specialist facilities

•Ultrasonography can be of value in establishing the extent of the damage and whether there is any retained foreign material

Treatment

•Surgical intervention is not normally required unless foreign material is present, there is gross loss of alignment or the orbital contents have become entrapped; such cases are best referred to a specialist centre

•In the majority of animals, medical therapy with broad-spectrum systemic antibiotics and anti-inflammatory agents is required, as is some form of topical ocular lubricant if exposure keratopathy is a likely complication

BLUNT AND PENETRATING INJURY TO THE GLOBE

Ocular trauma is caused by a variety of moving and static objects. Referral may be an early option for accurate assessment of the damage.

The prognosis is guarded with various types of penetrating injury because infection is a possibility, especially following cat claw injury and when foreign material is implanted in the lens or vitreous. Endophthalmitis (severe intraocular inflammation which does not extend beyond the sclera) may develop.

Blunt trauma is often more damaging to the globe than penetrating injury as the globe may actually rupture under the force of the impact (Figure 2.1(a,b) and, even when rupture does not occur, the shearing forces generated within the eye may cause severe damage to the intraocular tissues (Figure 2.8). The impact may be great enough to cause the globe to collapse, but more commonly the posterior scleral coat ruptures and this damage will not be apparent on ophthalmic examination.

Clinical signs

•The anterior segment triad associated with pain (blepharospasm, lacrimation and photophobia) is invariably present

•Blepharoedema and possible accompanying eyelid damage

•Other injuries to the head and elsewhere on the body may be present

•Corneal opacity (e.g. panstromal oedema) or obvious injury (e.g. laceration)

•Aqueous flare (protein-rich aqueous) – apparent as a subtle alteration in the transparency of the aqueous in the anterior chamber

•Aqueous leakage is likely when there is an acute penetrating injury (aqueous coagulates in air and may provide a smooth coating to an underlying prolapsed iris)

•Alteration in depth of the anterior chamber (usually shallower than normal)

•Intraocular haemorrhage (hyphaema or whole eye) can be a feature of both blunt and penetrating injuries

•Irregular or constricted pupil; if there has been full-thickness perforation the pupil margin and iris are often drawn towards the hole in the cornea.

•Thickened inflamed iris in which the fine detail is no longer apparent. Iris prolapse,

± iris incarceration, is a likely feature of penetrating injury. Blunt and whiplash injuries in animals with granula iridica may result in partial or complete avulsion and local haemorrhage. In animals where the drainage angle can be inspected directly, particularly horses, some tearing of pectinate fibres may also be observed following blunt trauma

•Lens luxation or signs of lens damage (e.g. capsular tears and leakage of lens material)

•Lens perforation is best appreciated by careful examination of the anterior chamber with magnification and a light source, looking from the side. Traumatic damage to the lens can result in a number of early-onset sight-threatening and painful complications, so it is sensible to refer such cases quickly for specialist assessment

•Vitreal changes (e.g. detachment of the vitreous face, subhyaloid haemorrhage [i.e. haemorrhage beneath the vitreous])

•Hyperaemia ± oedema ± haemorrhage of the optic nerve head (papilla)

•Peripapillary oedema and haemorrhage

•Retinal and choroidal oedema ± haemorrhage

•Retinal detachment

Diagnosis

•History and clinical signs

•Ophthalmic examination

•Measurement of intraocular pressure: low intraocular pressure is most commonly associated with uveitis, or globe rupture; high intraocular pressure is usually associated with glaucoma secondary to internal ocular pathology, but in trauma cases may, rarely, be a consequence of external pressure on the globe from, for example, extensive orbital haemorrhage

•Ultrasonography (or diagnostic imaging techniques such as MRI) may be useful for assessing the extent of ocular damage, especially if there are splits in the posterior ocular coats (retina, choroid and sclera), lens luxation, vitreal or retinal detachment and intraocular haemorrhage

OPHTHALMIC EMERGENCIES AND TRAUMA