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 second of two articles, the management of ocular emergencies, including sudden onset blindness, corneal oedema and diabetic cataracts, are discussed.

Ocular emergencies include all conditions of the eye that are painful, can result in vision loss or even loss of the eye. This article will address sudden onset of blindness, corneal oedema and diabetic cataracts.

Sudden onset blindness

Loss of vision can be caused by a variety of conditions including:

   loss of transparency of ocular media, such as cornea, lens or intraocular fluids not allowing light to enter the eye in an adequate manner (ocular inflammation, cataract formation, for example)

   loss of retinal function, when the retina is unable to process the incoming light into a nerve signal (sudden acquired retinal degeneration [SARD], retinal detachment, for example)

   loss of transmission of nerve signals between the retina and the brain resulting from reduced or non function of the optic nerve. Causes may include inflammation or neoplasia.

   lack of processing of the transmitted signals as a consequence of brain dysfunction (inflammation, neoplasia, intoxication, for example).

Initial contact with the owner/phone advice

Dogs with sudden loss of sight should be examined as soon as possible. Their owners should be questioned about possible exposure of the dog to toxic substances, particularly anti-parasitic medication, including ivermectin-containing products or horse wormer, and the presence of associated neurological signs.

Handling of the patient in the practice/hospital

The owners will be very concerned about their blind pet. Offering them a quiet place – to avoid disturbance of the pet – might be beneficial. Remember to talk to the patient too and help the owner to guide it into the consultation room.

Monitor the patient for any other neurological or behavioral abnormalities and inform the veterinarian if any signs are present.

The diagnostic procedure for blind patients will include an ophthalmic examination and might include additional diagnostic tests, such as an electroretinogram – electrophysiological testing of the retinas response to light – to assess retinal function (Figure 1), a neurological examination and, possibly, advanced diagnostic imaging such as magnetic resonance imaging or computed tomography, depending on the initial findings.

Figure 1: An electroretinogram can help to assess the retinal function. Light is flashed into the dog s eyes and the response of the retina is recorded

Treatment and management

Treatment will depend on the diagnosed condition and, again, it is important to ensure that the owner is confident in giving topical and oral medication as needed.

While some conditions that cause sudden onset vision loss can be treated successfully (for instance, cataracts) some patients will remain permanently blind (for instance, in cases of SARD). In these cases, many owners will be concerned about their dog’s quality of life and may even consider euthanasia. However, in our experience, most dogs cope incredibly well with the loss of vision as they use their other senses – such as smell and hearing – to compensate; but adaptation might take some time.

Generally, another dog that can function as a guide dog’, makes the adaptation process easier. The book Living with Blind Dogs by Caroline D Levin provides excellent support for the owner. It describes ocular anatomy and explains in detail different reasons for blindness in dogs. Several chapters describe how dogs cope with blindness and ways to help them in this new situation.

Corneal oedema

Corneal oedema describes an increase in water content within the cornea and can indicate a variety of ocular conditions. In a healthy eye, the cornea is completely transparent, partly as a consequence of its dehydrated state.

The outer (epithelium) and inner (endothelium) layers maintain the dehydrated state of the cornea. Disturbance of either of these layers will result in an increased water content and, therefore, oedema; resulting in a bluish appearance of the cornea.

Reasons for corneal oedema include a disrupted corneal epithelium caused by corneal ulceration, which can be diagnosed using the fluorescein test. After applying fluorescein to the eye and flushing excess dye away, the corneal stroma will appear fluorescent green in case of disruption to the overlying epithelium.

Epithelial lesions, however, usually result in a focal – and often mild – corneal oedema. More severe oedema, resulting in a diffuse bluish appearance of the cornea, is usually caused by damage to the corneal endothelium. This single cell layer serves as a pump that constantly removes fluid from the cornea. If it fails to work, the cornea becomes hydrated and loses transparency.

Reasons for the endothelium to stop working include intraocular inflammation, glaucoma (Figure 2) and endothelial degeneration. Intraocular inflammation (uveitis) – as well as glaucoma – are sight-threatening ocular conditions and, therefore, any patient with corneal oedema should be treated as an emergency. Ruling out glaucoma should be the first priority.

Figure 2: Right eye of an 8-year-old Labrador Retriever with glaucoma Note the diffuse corneal oedema and the redness of the eye

Glaucoma describes an increase in intraocular pressure (IOP) caused by an impaired drainage of aqueous humour. The raised IOP causes damage to intraocular structures, particularly to the retina. Depending on the severity and length of time of the IOP increase, this damage can be temporary or permanent. A very high IOP can render the eye permanently blind within a few hours.

Glaucoma patients don’t always show overt ocular pain, but are subdued and “just not right” owing to a headache. There are different tonometers to measure the IOP; but if one is not available, the IOP can be estimated by means of digital palpation.

The examiner stands in front of the dog with both thumbs under the dog’s chin, both middle fingers on the orbital rim (left finger on right orbital rim and vice versa). The indicator fingers are placed on the upper eyelids putting gentle pressure on the globes comparing their resistance. It is essential to compare the diseased eye with the normal one.

This method is very inaccurate and unreliable and referral to a practice with a tonometer should always be preferred.

Owner contact/phone advice

Dogs with eyes that appear opaque or blue should be seen as soon as possible, ideally within a matter of hours, since if not treated early an increased intraocular pressure can render an eye blind within a few hours.

Handling of the patient in hospital/practice

It should be a priority to rule out a raised intraocular pressure. In patients with a suspicion of a raised IOP, any tension to the neck should be avoided to prevent a further increase in the IOP.

Treatment and management

Treatment and management will depend on the diagnosis. Ocular medication will usually be required in cases of intraocular inflammation and glaucoma and, therefore, the owner should be confident about applying eye medication.

In glaucomatous patients, the use of a harness rather than a collar should be recommended to prevent a rise of the IOP when the dog pulls on the lead.

Diabetic cataracts

Diabetes mellitus is a common cause of cataracts in dogs. Half of all diabetic dogs develop cataracts within six months of diagnosis (80% within 470 days).1 The development of diabetic cataracts is related to the increased glucose levels within the lens (Figure 3).

Figure 3: A dog with diabetic cataracts

Striking characteristics of diabetic cataracts include a sudden and symmetrical onset as well as a dramatic swelling of the lens. Diabetic cataracts can result in an eye-threatening intraocular inflammation (Figure 4).

Figure 4: A dog with diabetic cataracts and lens-induced uveitis. Note the ocular redness, the irregular pupil and the hazy appearance of the cornea, that will make surgery difficult

Clinical signs include discomfort – characterised by blepharospasm (squinting), epiphora (tearing) and ocular redness. Changes in pupil size may be present, including miosis (reduced pupil size) in cases of acute inflammation or dyscoria (irregular pupil shape) caused by adhesions between lens and iris (synechiae).

Inflammatory changes of the posterior segment might also be present – for example, hyalitis which is inflammation of the vitreous body, retinal detachment. An ocular ultrasound and electroretinography can help to identify these changes.

Owner contact/telephone advice

It is essential to discuss the likelihood of cataract development in all diabetic patients at the time of diagnosis. In the event of sudden loss of vision, or a white appearance of the eye, assessment for cataracts should be performed as soon as possible. Instigation of treatment with non-steroidal anti-inflammatory eye drops might be indicated.

Handling of the patient in hospital/practice

Diabetic patients that develop cataracts should be referred to an ophthalmologist as soon as possible to discuss the option of cataract surgery. Always inform the ophthalmologist that the dog is diabetic, so that an early appointment can be arranged.

Treatment and management

Any degree of intraocular inflammation caused by the cataract should be treated and is best avoided by early cataract surgery; because if a lens-induced uveitis develops, it can make cataract surgery more difficult and can decrease its success rate. Indeed, it may render surgery unfeasible, or prohibit the placement of an intraocular lens.

Anaesthesia of unstable diabetic patients is often a concern and can result in a late referral. However, experienced anaesthetists will adjust their protocols and monitor patients closely, making anaesthesia and recovery as safe as possible.

It is essential for owners to understand that intensive ocular medication is necessary after cataract surgery; particularly during the first few weeks after the surgery, when patients might require up to 10 drop applications a day to the operated eye. Many dogs will be weaned off medication completely over a period of several weeks, while some might need life-long medication.

As with any surgery, cataract surgery also has complications, such as glaucoma or retinal detachment. Both conditions, which may potentially lead to blindness, can occur any time after the surgery. Therefore, regular check-ups, often for the rest of the pet’s life, will be recommended by the ophthalmologist.

These articles have provided an overview of the conditions of which the veterinary nurse should be aware; and for nursing staff with a deeper interest in patients with ophthalmic diseases, Sally Turners book Veterinary Ophthalmology: A Manual for Nurses and Technicians provides further reading. 


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 completed 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.2045-0648.2012.00248.x or Veterinary Nursing Journal Vol 27 pp 454-456


1. BEAM. S.. CORREA. M. T. and DAVIDSON. M. G. [1999] A retrospective-cohort study on the development of cataracts In dogs with diabetes mellitus: 200 cases Vet Ophthalmol 2[3]:169-172.


• VOL 27 • December 2012 • Veterinary Nursing Journal