ABSTRACT: Ocular emergencies are commonly encountered in general practice Understanding the different disease processes of the most common conditions will help veterinary nurses to give adequate advice to the distressed owners and will ensure that the patients are cared for in the best possible way. The nurse's role during the conversation with the owner, particularly in view of recognising the seriousness of the condition as well as owner education during the treatment period, should be emphasised In this first of two articles, the management of the two most common ocular emergencies, proptosis or prolapse of the eyeball and corneal ulcerations, are discussed.
Ocular emergencies include all conditions of the eye that are painful, can result in sight loss or even loss of the eye. Recognising ocular emergencies is essential in order to begin adequate treatment to preserve vision and ensure the patients comfort.
This first of two articles will address proptosis (or prolapse) of the globe and corneal ulcerations.
Ocular anatomy
The eye is protected within a bony cavity called the orbit. The canine orbit is open, meaning that part of the orbital wall is composed of muscles and connective tissue rather than bone. The eye is supported by a fatty cushion within the orbit and its movement is facilitated by seven extraocular muscles that connect the globe with the orbital wall.
The globe is also protected by the eyelids, the conjunctiva and the pre-ocular tear film. Eyelid closure protects from traumatic injuries and spreads tears across the ocular surface.
The globe itself consists of three layers. The outer fibrous layer, composed of the transparent cornea and the white sclera, protects the eye as well as providing its shape. The second layer is the uvea. This is the most vascular layer and consists of the iris, the ciliary body and the choroid.
The inner layer is the retina, which is the part of the eye where the incoming light is converted into a nervous impulse that is then sent to the brain via the optic nerve.
Another specialised structure within the eye is the lens, which focuses the light onto the retina. The lens is connected to the ciliary body by numerous tiny ligaments called zonules. Varying the tension on these zonules changes the lens shape and, therefore, its refractive power, allowing the eye to focus on objects at different distances – a process known as accommodation.
The health of the intraocular structures is very dependent on the intraocular fluid – the aqueous humour that is produced by the ciliary body. It provides nutrition for avascular structures, such as the lens and the cornea, keeps the shape of the eye stable and serves to remove metabolic waste products.
It is drained out of the eye via the iridocorneal angle that is composed of a nieshwork that eventually connects with the venous vasculature of the eye. Balance of aqueous production and outflow – a stable intraocular pressure – is essential for ocular health.
Proptosis of the globe
Proptosis of the globe describes the forward displacement of the globe, often with entrapment of the globe in front of the palpebral fissure, preventing spontaneous reposition. In brachycephalic breeds (such as the Pug, Pekingese and Shi Tzu) proptosis of the globe is much more common and can occur following minimal trauma.
The forward movement of the globe often results in tension and damage to the optic nerve as well as the extraocular muscles. The more severe the proptosis, the greater the risk of permanent vision loss.
Owner contact/phone advice
When contacted by an owner who describes their dog’s eye as falling out or protruding, the immediate advice should be to consult a veterinary surgeon as soon as possible, followed by instructions as to how to protect and lubricate the globe.
A towel soaked with cold water will provide both protection and lubrication of the ocular surface and the cold might reduce or prevent further swelling. Depending on availability, artificial tears can also be used to lubricate the ocular surface.
Handling of the patient in the practice/hospital
The dog should be handled as carefully as possible, and sedation or anaesthesia be considered by the veterinary surgeon early in the examination and treatment process.
Treatment and management
Depending on the severity of the condition, treatment may include:
• enucleation (removal of the eye)
• reposition of the globe and placement of a temporary tarsorrhaphy (surgical closure of the palpebral fissure for a period of time)
• medical treatment by means of lubrication and systemic anti-inflammatory medication in mild cases (i.e. if the dog is still able to cover the whole cornea with its eyelids when it blinks).
Prognosis for vision is poor. Only 20 per cent of these cases retain full vision following trauma of this nature and the dogs often develop a strabismus resulting from tearing of the extraocular muscles (Figure 1).
Figure 1: 4-year-old Lhasa Apso with proptosis of the right globe. Note the lateral strabismus resulting from a torn medial extraocular muscle
Long-term complications also include a lagophthalmos (incomplete blink), reduction or absence of corneal sensation and keratoconjunctivitis sicca (dry eye). It is important to educate clients with brachycephalic dogs about the risk of a proptosis. Owners should avoid putting any tension on their dogs neck or scruff.
A permanent tarsorrhaphy to reduce the size of the palpebral fissure can provide some mechanical support to try and prevent a proptosis to occur. The benefit of this procedure depends on the individual dog’s facial conformation and should be discussed with the veterinary surgeon or ophthalmologist.
Corneal ulceration
A corneal ulcer is a wound of the cornea. Ulcers are painful and can, depending on depth and extension, result in reduced stability of the cornea, with the potential of rupture and subsequent loss of the eye, if not treated effectively.
Corneal ulcers can be divided into superficial and stromal ulcerations. In a superficial ulcer only the outer corneal layer, the epithelium, is lost (Figure 2).
Figure 2:. 7-year-old Boxer with a superficial corneal ulceration. Only the superficial layer of the cornea (epithelium) is missing, the mechanical stability of the eye is maintained
The epithelium acts as a protecting barrier
, preventing infection of the underlying stroma. The mechanical stability of the eye is not impaired; therefore, preventing bacterial infection and providing pain relief are the two important aspects of treatment.
In cases of stromal corneal ulceration, both the epithelium, as well as the corneal stroma, are damaged resulting in reduced mechanical stability of the eye (Figure 3).
Figure 3: A Pug with a deep stromal corneal ulcer. Note the extensive tissue loss making this eye very fragile. There is brown tissue and blood visible in the ventral aspect of the ulcer, consistent with a perforation and iris prolapse. This is a surgical emergency
Stromal ulcers are best diagnosed from the side, since they result in an indentation of the ocular surface. Any stromal ulcer has to be taken extremely seriously! A so-called melting corneal ulcer – in which bacteria or inflammatory cells produce enzymes (collagenases) that degrade the stromal tissue – can progress to a corneal perforation very quickly, sometimes within a few hours.
Owner contact/phone advice
Dogs should be seen on the same day that the owner notices problems with the eye. Particular notice must be taken if they describe signs such as ocular discharge or redness, squinting or tearing.
The owner should be advised against bathing the eye before the dog has been assessed by a veterinarian. Typical household remedies, such as cleaning the eye with tea, should be discouraged.
Handling of the patient in the practice/hospital
It is important that patients with stromal corneal ulcerations are handled with the greatest of care. Avoid putting any pressure on the eye or neck. Buster collars should always be opened before removing them rather that pulling them over the head. The latter might result in a rupture of a fragile eye.
For the examination, an appropriate level of sedation should be considered. Patients with fragile eyes must not be subjected to forceful restraint – for example, when administering oral medication – and the parenteral route should be considered if the patient resists.
Treatment and management of stromal ulcers
Depending on the depth and extent of the stromal corneal ulceration treatment options include intensive medical treatment with antibiotics and collagenase inhibitors (to stop the degradation or ‘melting’ of the cornea) as well as systemic antibiotics and anti-inflammatory medication.
If the ulcer is very deep, the veterinary surgeon might opt for grafting procedures, such as: conjunctival pedicle grafts, in where a pedicle-like piece of conjunctiva is sutured into the ulcer bed; corneoconjunctival transposition (the cornea is split horizontally into two layers and the upper one is transposed into the cleaned ulcer bed); corneal, or amnion graft, which involves the use of donor cornea or amnion to replace the missing tissue (Figure 4).
Figure 4: The same Pug as in Figure 3 approximately two weeks after receiving a corneal graft
Most of these are specialist procedures and will be performed in referral hospitals. Initially, avoidance of self-trauma by using a Buster collar is essential. The use of a harness rather than a collar is generally recommended for eye patients with fragile eyes. The veterinary nurse can also play an important role in supporting the owner who needs to be comfortable with applying ocular medication, as well as understanding the importance of so doing.
It is essential to discuss long-term management with the owners. Stromal ulcers can cause significant scarring and vascularisation of the cornea, giving the eye an unusual appearance. Vascularisation can be of particular concern and the owner might need reassuring that a red appearance is often part of the healing process.
While many ulcers are caused by trauma, some are associated with other ocular diseases such as dry eye, which often requires life-long therapy to prevent recurrence of corneal ulcers or other complications, such as opacification of the cornea.
Administration of eye drops
The easiest way to give eye drops ^ single-handedly is to adopt the following approach:
• place the dog either on your lap or in front of you on the floor facing away from you
• put one hand under the dog’s chin preventing any backwards movement with your body
• take the opened ointment or eye drop bottle in the other hand and rest this hand on the dog’s head
• open the eye by moving the facial skin towards you, and at the same time place the bottle over the palpebral fissure to apply the drop or ointment
• repeat with the other eye as necessary.
The advantage of this method is that the dog can’t escape backwards and does not see the bottle approaching. Positioning the bottle/tube over the dog allows administration using gravity and avoids contact with the eye, thus preventing contamination of the bottle or traumatising the patient.
The second part of this article will focus on ophthalmic emergencies and conditions, including corneal oedema, sudden onset blindness and diabetic cataracts.
Author
Claudia Busse DipECVO CertVOphthal MRCVS
After qualifying from the School of Veterinary Medicine, Hanover, in 2004, Claudia spent one and half years in general practice while preparing a doctoral thesis on hereditary eye diseases. She then went on to complete an internship at the Animal Health Trust, Newmarket, and subsequently commenced a Residency in Veterinary Ophthalmology, which she comp
leted in 2009. She successfully passed her European Diploma exams in Veterinary Ophthalmology in 2010 and currently works as a clinician in the Unit of Comparative Ophthalmology at the Animal Health Trust.
To cite this article use either
DOI: 10.1111/j.2045-0648.2012.00238.x or Veterinary Nursing Journal Vol 27 pp 406-408
Veterinary Nursing Journal • VOL 27 • November 2012 •