VETcpd - Ophthalmology Peer Reviewed Obvious Ophthalmology: Corneal Ulceration Corneal ulcers can range from a simple superficial corneal abrasion after mild trauma, that will heal by itself in a few days, to a deep crater reaching far into the stroma, which may result in a corneal perforation and loss of the eye. The key to managing this diversity of ocular surface lesions is to ask first what is causing the ulceration: Is there infection, an irritating factor such as a foreign body, an aberrant lid hair, or dry eye preventing ulcer healing? Or maybe the problem is a defect in the corneal basement membrane itself? Secondly, the depth of the ulcer must be defined by close assessment of simple features such as the reflection of light at the edge of the ulcer and the degree of stromal haze apparent at the centre of the ulcer. Thirdly, the degree to which healing is taking place must be assessed. With answers to these questions, a treatment plan can be devised either with simple topical antibiotic and tear replacement, or with protection of the corneal surface using application of a polymerised hyaluronic acid gel to facilitate healing, or in specific cases, with surgery such as grid keratotomy, diamond burr debridement or a Dr David L Williams MA, conjunctival flap. VetMD, PhD, CertVOphthal, Key words: Corneal ulcer, eye, dog, epithelium, stroma, healing CertWEL, FRCVS David qualified from Cambridge in Introduction Three simple questions 1988, aiming to devote his professional One of the problems In assessing any corneal ulcer three life to veterinary ophthalmology. resulting from the pau- questions need to be asked. First, what Having worked at the Animal Health city of ophthalmology caused the ulcer? Second, how deep is Trust and Royal Veterinary College, teaching in many UK the ulcer? And third, is the ulcer healing? gaining his CertVOphthal and PhD, he returned to Cambridge, studied for his veterinary schools over Once we have the answer to those three FRCVS, CertWEL and VetMD and now the past ten years is that questions, defining the treatment option
teaches ophthalmology there as well as Photo: © iStockphoto.com there is a considerable that is most appropriate will hopefully exotic animal medicine, animal welfare population of veterinary surgeons who do be relatively straightforward. It can be and ethics. not feel sufficiently equipped to deal with difficult, however, to answer the first His latest foray into postnomials is a ocular conditions which are relatively question, regarding the definitive aetiology Masters in Education to improve his common and can be concerning in that of the ulcer, although we can have a teaching skills. they can result in both pain and blindness. reasonable index of suspicion. Fellow and Director of Studies, Of these, the corneal ulcer stands out as Take these three cases as examples: Veterinary Medicine and Pathology a particular problem. A key issue here is St John’s College, Cambridge CB2 1TP A young bouncy crossbred returns from that the different techniques to deal with an afternoon in the woods with a closed Associate Lecturer in Veterinary the corneal ulcer are useful in particular weeping eye. We assume that a traumatic Ophthalmology Department of ulcers but can be counterproductive, to incident with a low hanging branch or a Veterinary Medicine, Madingley Road, put it mildly, in others. A grid keratotomy, Cambridge CB3 0ES thorny bush is responsible for the ulcer for instance, can promote healing in a causing his ocular pain but it is difficult to Tel: 07939074682 superficial non-healing ulcer but may be sure. A cat wakes up one morning with E: [email protected] lead to globe rupture if used in a deep a red eye with rather swollen conjunctiva www.davidlwilliams.org.uk stromal ulcer. What is needed is a clear and a wide superficial corneal erosion set of criteria to diagnose different types which may be a manifestation of feline of corneal ulcers and a set of treatment
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VetIndex 2014 corneal pathology. Dipl. EVDC Rossdales quine Hospital Hospital quine e istry acti pR quine e Rossdales Boben c Partridgeiagnostic d & ry Specialist in Dent e R t ce European Veterina New Exning, ot c t R Beaufo C Beaufort is pleasedt marke to offer dental training, practice seminars, but this presentation is not particularly ta Sta ttage o ge ge bles, lasia, ies R ato R o B a l a Newm eet, r St High re dicine, me y, urger s rket advice,production assistance and referral services for:- periodontal, os diagn cal i clin and cial Trauma, Neop alth including ambu ce cti pra ocal l loc for tics s, Tooth tory serv tory la al a practice mmunity & energy a Newm eet, r St High and ce i out-of-h Dentalser l Cases,referra nd Fa rket tele ours vices tions, Orthodontic Promotes and maintains whole body he 20th Edition ervice s one ph aging. Complex3 Extrac016 el: t intestinal, cardio-vascular, skin & joint health, i 6 8 0163 el: t 4 57775 8 Oral Clearance, Im 63150 ® y atholog p linical c Fractures, Crowns, site at at site web our visit 01633 612595 t www.rossdales.com Spec 663017 01638 el: OakBeck Veterinary Hospital www.petplus.info Harrogate, HG1 3HU 01423 - 561414ou and The Understanding the aetio-pathogenesis of common, and a large superficial erosion Actively Supporting y ip your Client Relationsh yearround guide each ulcer type is needed to be able to may be a more frequent manifestation of
to veterinaryto products, suppliesand services base therapies not just on a flow-diagram this virus in the feline ocular surface. A alone, but more fundamentally on a grasp third example is a middle-aged female
to veterinary 2014year round guide The products, supplies and services For Ophthalmology of the underlying pathology occurring neutered West Highland White Terrier Referrals in your area: in each ulcer. Here we will concentrate which presents with a mucopurulent vetindex.co.uk/eyes on the canine cornea and leave the feline discharge and an obvious crater in the www.vetindex.co.uk counterpart for a future discussion. central cornea.
Page 28 - VETcpd - Vol 1 - Issue 3 VETcpd - Ophthalmology
The first step in each case is to perform a Schirmer tear test, as an ulcer associated Epithelium with dry eye is a common finding in a dog of this breed, age and sex. Each of these cases needs very different management, as we will see below. First however, we must take a moment to review the normal anatomy of the cornea. Stroma
A review of normal corneal anatomy A moment’s thought will remind us just how remarkable the cornea is. At around Descemet’s 600 um thick, the cornea has a protective membrane epithelium, a dense collagenous stroma Endothelium lined by an endothelium (Figure 1) giving a tough resilient structure. The very Figure 1: Histological appearance of the normal Figure 2: The regular arrangement of collagen word “cornea” has its etymology from cornea with epithelium, stroma, Descemet’s fibrils rendering the cornea transparent. the Latin “cornu” or horn, given its hard membrane and endothelium. consistency, yet we have a tissue which is transparent – biological glass we might say – at least until trauma or infection strikes. This transparency is associated with the remarkable regularity of the protein content of the corneal stroma and the relative paucity of cells packed with Epithelium organelles that would otherwise diffract light. The protein is of course collagen fibrils, each of them the same diameter, around 20-25 nm, spaced equally apart Stroma by a similar distance (Figure 2). Why does this give transparency? The wavelength of visible light is between 450 and 600 nm and so one can see how light beams Figure 3: The continual movement of corneal epithelial cells in what Dr Richard Thoft termed the X, Y, Z arrangement with basal cells migrating centrally from the limbus (X), moving up the stratified traversing the corneal stroma are not squamous layers of wing cells (Y) and the desquamating cells from the corneal surface (Z) as the lids being influenced by the protein which brush across, giving a continual healing response for any epithelial erosion in a healthy cornea. holds the cornea together even though protein density is high - the regularity of the collagen fibrils which provide over its surface, so the corneal epithelium This arrangement of continual epithelial the cornea with its structural integrity with its impervious lipid membranes replacement means that a normal corneal render them ‘invisible’ to the light rays and tight junctions is key in preventing epithelial erosion should heal in a very passing through them. ‘Invisible’ as long fluid ingress into the corneal stroma. It is few days. If a corneal ulcer just involving as their regularity is maintained. Increase this barrier which is breached with any the epithelium presents itself, it is worth the amount of water in the cornea, and corneal erosion or ulcer, and it is indeed rechecking again 3-5 days later; if there the collagen fibrils separate themselves to remarkable that any such damage does is no healing, then further investigation different degrees and the regularity is lost. heal, since fluid entering the anterior is warranted. Often it is the basement In fact there is always plenty of water in stroma would appear to be a serious membrane upon which the epithelium the cornea - it accounts for about 78% impediment to ulcer healing. The answer rests, anchored by a complex set of of its wet weight. However, this water is to this conundrum is that the corneal adhesion molecules (hemidesmosomes), bound to proteoglycans (keratin sulphate epithelium is actually always healing that is abnormal. While the epithelium and chondroitin sulphate) in the healthy itself. Every time we blink, a proportion heals rapidly, it can take the stroma a much cornea, and these molecules are themselves of the most anterior cells of the corneal longer time to heal, primarily because in attached to the collagen fibrils at specific epithelium desquamates into the tear order to keep the cornea transparent, it has sites. The corneal endothelium has the task film. As this loss of cells occurs, they are very few keratocytes, the very cells which of actively pumping any unbound water replaced by cells originating in the stem should be producing new stromal collagen out of the corneal stroma and back into cell population which resides at the limbus, fibrils. So quite often a mid-depth ulcer the aqueous humour. so cells continually migrate from the will epithelialise well before the stromal limbus into the central cornea at the base extracellular matrix has replenished itself. All of this seems a long way from corneal of the stratified squamous epithelium, and This results in a facet, which can all too ulceration, except that the front of the then rise through the layers of cells, now easily be confused with an ulcer, unless cornea is just about as bathed in water termed wing cells, before desquamating one is careful about assessing the ulcer as the back, with a tear film constantly from the surface (Figure 3). meticulously.
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