Common Ophthalmic Emergencies Part 1: How to Triage the Eye Georgina Fricker BVSc MRCVS CertVOphthal DipECVO RCVS and European Specialist in Veterinary Ophthalmology www.vet-eCPD.com www.centralcpd.co.uk Ophthalmic Emergencies Session 1: How to triage the eye The aim of today’s course is to describe common conditions of the eye and adnexa in canine and feline patients requiring urgent action to avoid pain, loss of vision or even loss of the globe. As well as providing useful information regarding these conditions we plan to provide practical advice to improve clinician confidence when tackling these cases. We will work through several cases and use a problem-oriented approach to explore the common ophthalmic emergencies seen in our canine and feline patients. The dictionary definition of an emergency is a sudden, urgent, unexpected occurrence or occasion requiring immediate action. Ocular emergencies are typically acute, painful conditions with analgesia and sometimes sedation required to facilitate examination. A full ocular examination should be performed where possible, with full physical examination (including neurological assessment) imperative in any case related to trauma. We will discuss approach to the initial examination and how best to develop a diagnostic and therapeutic plan to stabilise the globe in the emergency situation with the aim to return comfort and preserve vision long term. Questions to consider when assessing an ophthalmic emergency 1. Is the animal otherwise stable? 2. Is the animal painful? 3. Is the globe intact? 4. Can the eye see? As with any other case a good history can help to understand the lesion presenting. Once a thorough physical examination has been performed we can consider signs of ocular pain. The animal’s general demeanour and posture, vocalisation, respiratory rate, blink rate and epiphora are good clinical indicators of discomfort that can be assessed from a distance. On closer examination response to touch and heart rate can add to the assessment, alongside response to analgesia which has been argued to be the most reliable indicator of pain in animals. Remember that opioid analgesics can influence pupil size and so if possible an initial examination of the eye should be performed before administering these drugs. Assessing the integrity of the globe can be difficult, particularly if there is marked swelling of the adnexa, or hyphaema. Observation of symmetry of the globes, and for ocular discharge can be performed from a distance. On closer examination fluorescein staining can help to identify corneal perforations, but perforation of the sclera may require further investigation such as ultrasound of the globe. If you do not feel confident assessing a potentially compromised globe, early referral is recommended. Careful testing of vision reflexes is not always reliable in a stressed individual but will add to the clinical picture. It is also helpful to assess ocular movement, particularly in cases of proptosis where this can help prognostic prediction. Don’t forget to check that the patient is physically able to respond by blinking using the palpebral reflex. Vision reflex/response Cranial nerves involved Menace response II & VII Dazzle reflex II & VII Pupillary light reflexes – direct & II & III consensual Vestibulo-ocular reflex III, IV & VI as well as vestibular system and medial longitudinal fasciculus of the brainstem Palpebral reflex V & VII Corneal reflex V & VII (+VI) Further vision testing if the menace response is equivocal includes visual tracking, visual placing (smaller patients) and maze testing (obstacles and steps). Ophthalmoscopy This will be a far more useful tool if you are familiar with your ophthalmoscope and its features, it is kept clean and you use it to check eyes regularly to build a mental database of variations of normal. Pattern recognition is a vital tool in clinical ophthalmology! Distant direct ophthalmoscopy can be performed at arms-length and allows assessment of pupil size and symmetry as well as localisation of any opacities (lesions) within the visual axis. Close direct ophthalmoscopy can then be used for fundic examination and closer examination of lesions anterior to this in the absence of a slit lamp. Many models have additional features such as a slit beam (useful for assessment of lesion depth in corneal ulcers, and for detecting aqueous flare), a graticle (useful for sizing lesions) and red-free (vessels or haemorrhage appear black, pigment appears brown) or cobalt blue (for fluorescein staining) filters. If your model of ophthalmoscope does not have a slit beam, then the smallest light beam at the brightest setting can be used to detect aqueous flare, held close to the eye and at an angle to the observer’s line of sight. This will need to be performed in total darkness for best success. Indirect ophthalmoscopy provides a wider overview of the fundus, in a lower magnification inverted image. In cases with cloudy ocular media this technique may allow a better view of the fundus than direct ophthalmoscopy. Use of a binocular headset not only frees one of the examiner’s hands, but also provides stereopsis. Where possible tests such as the Schirmer tear test, intraocular pressure measurement and fluorescein staining should be included. If a surface infection is suspected, sampling should be performed under local anaesthetic before fluorescein staining in case immunofluorescent techniques are required. Cytology samples may be collected using a cytobrush, or (non-cutting) back end of a bard-parker no.15 blade and microbiology samples with a fine-headed cotton swab placed in charcoal media. Fluorescein is a vital stain that is water-soluble and will stain hydrophilic tissues such as the corneal stroma in epithelial defects and also conjunctival erosions in feline herpesvirus-1 (FHV-1) cases. It is easily washed off hydrophobic tissues such as the corneal epithelium and Descemet’s membrane. As well as detection of corneal ulceration, fluorescein can be used to assess pre-corneal tear film health via the tear film break up time (TFBUT) and nasolacrimal patency (Jones test). Most useful in emergency cases is Seidel’s test for corneal patency. A generous amount of dye is applied to the eye and the eyelids are forced closed to distribute it. When the eyelids are opened the corneal wound will retain dye, but any leaking aqueous will create a dark ‘river’ as the dye is washed away. The cornea should be flushed with saline after fluorescein testing to remove excess dye which has a minimal ocular toxicity topically, but also to identify any stromal facets. Intraocular pressure measurement is most commonly performed using applanation (Tonopen, Reichert technologies) or rebound (Tonovet, Kruuse). The more basic indentation Schiotz tonometer, although accurate when used correctly, is not useful in cases with corneal pathology and requires conversion tables as well as restraint of the patient with the head in a horizontal position. As a guideline in dogs and cats normal intraocular pressure can be thought of as 10-25mmHg. Lower intraocular pressure is suggestive of uveitis and high pressure indicates glaucoma, both of these conditions are encountered as emergency presentations and we will consider them in more detail later in the day. Ocular ultrasound can be a useful auxillary diagnostic tool in cases with loss of clarity of the ocular media, or extensive swelling of the adnexa. Topical anaesthetic may be sufficient, but if the eye is very painful then chemical restraint should be used for mild sedation (avoiding ventral rotation of the globe). Transcorneal ultrasound with a linear, minimum 7.5MHz probe provides the best images of the globe. If the cornea is unhealthy then a transpalpebral approach may be safer, although the haired skin will create artefact, significantly reducing image quality. Care should be taken to avoid ultrasound gel entering the eye, preferably a sterile gel pouch should be used in cases with poor corneal health or potential perforation and only gentle pressure should be applied to a delicate cornea. Ophthalmic Emergencies Session 1: The cornea is fluorescein positive what next? Corneal ulceration Causes A corneal ulcer describes a break in the corneal epithelium exposing the stroma beneath and is associated with fluorescein uptake. Superficial, uncomplicated ulcers should heal rapidly (3-5 days) whilst those involving the stroma often require intensive medical or even surgical intervention. In clinical practice, most corneal ulcers are assumed traumatic in origin but there are many other causes. It is important to assess eyelid conformation, structure and function, Schirmer tear test values, tear film break up time and check for eyelash abnormalities (ectopic cilia/distichia) in both the affected and contralateral eye. Infectious keratitis is rare in dogs, although more recently clinical cases of canine herpesvirus causing superficial dendritic ulceration have been reported. Cats of course do experience a high rate of infectious keratitis which is typically acute, with extensive epithelial loss, focal oedema and a lack of cellular infiltrate or malacia. It is vital to examine carefully and find the cause (if possible) in order to treat effectively. If the ulcer has not healed after 5 days, you need to investigate why. Was it infected, has it become infected or is it indolent? Use of topical steroids in superficial ulceration can risk secondary infection and keratomalacia. If corneal melting occurs then there can be rapid loss of corneal stroma, potentially resulting in corneal perforation within hours, these cases become a true emergency. Management Exposure of the corneal stroma increases the risk of bacterial adherence and colonisation; all corneal ulcers should therefore receive broad spectrum topical antibiotics (e.g. Chloramphenicol, Fusidic acid). If infection is already suspected (yellow/white cellular infiltrate in cornea, marked corneal oedema, mucopurulent discharge) then microbiological culture and cytological evaluation is recommended to allow focussed treatment and should be performed before application of fluorescein (which can interfere with immunofluorescent techniques in the laboratory).