Ivj dec 2009.indd

Equine corneal ulcers
Natasha Mitchell offers an insight into equine corneal ulcers and gives practitioners advice on performing an examination Natasha Mitchell, MVB CertOpthal MRCVSCrescent Veterinary Clinic, Dooradoyle Road, Limerick, IrelandE-mail: [email protected] Corneal ulceration is a common sight-threatening problem such as a blunt injury sustained while out hunting. Duration in horses which regularly presents to mixed practice and and progression of the problem are also important pieces equine veterinary practitioners. The severity of corneal of information for a vet to obtain. Symmetry of the face and ulcers can vary greatly, and the outcome depends on rapid orbital area also need to be assessed. diagnosis, early instigation of appropriate medical and/or Vision tests also must be performed these are, however, surgical treatment with both patient and owner compliance. pretty basic. Wave your hand towards one eye at a time, Deep ulcers, melting ulcers and descemetocoeles are taking care not to create an air current which could be emergencies as they may very rapidly progress to globe felt by the horse. A normal reaction for the animal is to blink and possibly partially retract the head, known as a menace response. Shine a bright light into the animal's eye to perform a dazzle reflex. A normal reaction is to blink The aims of a clinical examination are to assess whether and attempt to look away. The pupillary light response is the horse can see; to look for signs of trauma such as checked by shining a light in the eye and observing for the facial lacerations; to examine the extent and depth of the expected pupillary constriction. ulcer; to assess the presence of any factors which would The safety of the handler, the attending veterinarian and the complicate healing; to assess as to whether appropriate patient during this examination are very important, and it is treatment is medical or surgical; and, to decide on how reasonable to consider sedating any horse which requires medications may be delivered to the eye.
a detailed ocular examination. Sudden movements by the Whatever the eye complaint, it is best to carry out an horse can impact against the instrument being used to examination in a systematic manner, in order to reduce examine the eye, which in turn can cause significant damage the likelihood of missing an important step. The animal's to the examiner's own eyes. For this reason, and because history can provide valuable information, as sometimes gentle patient handing is required in the case of deep horses with corneal ulcers have a known history of trauma, corneal ulceration, sedation of the animal is a good idea.
Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 818 24/11/2009 12:44:33 While tear deficiency is not a very common problem • Globe for enophthalmos, exophthalmos, in horses, it is worth performing a Schirmer tear test hydrophthalmos (enlarged globe suggestive of whenever there is ocular surface disease. Normal glaucoma), phthisis bulbi (shrunken globe), strabismus values are approximately 20-30 mm/minute. The value is significantly decreased if prior topical anaesthesia is • Ocular discharge and its nature: tears, mucoid, or applied. Eyes with low tear readings may have delayed mucopurulent (Figure 1);
corneal healing and require tear supplementation. A STT is • Eyelids for blepharospasm, the ability to blink, mobility, not performed on eyes with deep or melting corneal ulcers anatomical position, and injuries; due to the risk of trauma during the procedure.
• Conjunctiva and third eyelid for inflammation, mass Topical anaesthesia is very useful to provide for easier lesions and foreign bodies. It is preferable not to examination, to facilitate tonometry for intraocular pressure manually protrude the third eyelid by digital pressure measurement, and to allow scraping of the corneal surface on the globe as this could cause globe rupture; for cytology. It increases the horses compliance during • Cornea for oedema, neovascularisation, presence of examination by reducing pain. However, it should not be a foreign body, surface irregularities and iris prolapse used as a treatment for painful corneal ulcers as it inhibits (Figure 2);
• Anterior chamber depth (shallow, normal or deep), Nerve blocks are very useful when the eye is painful. turbidity (aqueous flare is a sign of anterior uveitis) Indeed, they are essential in the case of deep corneal and contents, e.g. blood (hyphaema) or inflammatory ulceration to reduce the likelihood of the cornea rupturing cells (hypopyon); and, during examination. A motor nerve block is performed by • Iris: position, colour, size of the pupil at rest and anaesthetising the auriculopalpebral branch of the facial mobility and shape of the pupil.
nerve (CNVII) which innervates the powerful orbicularis Examination with magnification greatly improves oculi muscle. The nerve can be palpated under the skin at visualisation of the corneal ulcer. Ideally a slit-lamp the highest point of the zygomatic arch, and it is blocked biomicroscope is used, but magnifying loupes, an otoscope by subcutaneous infiltration with 2-3 ml of lignocaine or or the direct ophthalmoscope on the +15 to +20 setting mepivacaine using a 25-gauge needle. A sensory nerve may also be used for this purpose. block is performed by anaesthetising the supraorbital All red or painful eyes should be stained with fluorescein nerve, which is a branch of the trigeminal nerve (CNV), dye routinely. Fluorescein is a water-soluble stain which is which is sensory to the central upper eyelid. The nerve hydrophilic and lipophobic. It is orange in colour, but turns exits from the supraorbital foramen within the frontal bone, green when it comes into contact with the alkaline pre- and it is blocked by the subcutaneous injection of local corneal tear film. There is no uptake in the normal cornea anaesthetic, as used for the auriculopalpebral nerve block. as the intact lipid-rich corneal epithelium provides a barrier. A combination of these blocks will reduce pain and stop However, when corneal ulceration is present, fluorescein spasm of the orbicularis oculi muscle, allowing the upper may gain access to the stroma where it uptakes. It is eyelid to be lifted and a more thorough examination to be most readily observed when viewed with a blue light, which causes the dye to fluoresce and highlights even small Next, examination with the naked eye is facilitated by breaks in the epithelium, and epithelial under-running may the use of a strong focal light source, for example a be appreciated. Figure 3 is a stromal corneal ulcer, and Figure
transilluminator, looking for gross signs of ocular disease 4 depicts the appearance after application of fluorescein.
Thus, a deep crater-like lesion with no fluorescein staining Figure 1: Mucopurulent discharge with blepharospasm in a pony with corneal
Figure 2: The eye of the pony featured in Figure 1 – the untreated central
corneal ulcer has ruptured resulting in prolapse of the iris.
Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 819 24/11/2009 12:44:35 type of cells involved are seen, for example neutrophils, lymphocytes, eosinophils, plasma cells and epithelial cells, but also the appearance of any bacteria in the form of rods or cocci will assist in making an informed antibiotic choice. Fungal hyphae may be seen.
Expected clinical signs include pain, blepharospasm, epiphora (Figure 1), slightly swollen eyelids, and conjunctival
hyperaemia. Depending on the cause and duration of the
problem, there will be a change in corneal appearance
such as oedema, neovascularisation, inflammatory cellular
infiltration (cream or yellow opacities), pigmentation, and
mineral or lipid deposition. There may be a crater-like
defect with or without a gelatinous appearance (melting).
There is fluorescein dye retention. Figure 3: Severe stromal necrosis in a pony.
Superficial uncomplicated ulcers are generally small in size, are shallow, and have no epithelial under-running at the edges of the lesion. Spontaneous chronic corneal
epithelial defects (SCCED) are superficial ulcers, with
surrounding non-adherent epithelium (Figure 5 and Figure 6).
Figure 4: Fluorescein staining of the deep ulcer featured in Figure 3.
at the base indicates a descemetocoele which is an emergency as the globe is in danger of perforation.
Anterior uveitis is frequently present when there is corneal ulceration due to reflex stimulation of the corneal sensory Figure 5: Superficial corneal ulcer with non-adherent epithelium at the ed ges.
nerves. This may be seen clinically as a constricted pupil There is corneal oedema and neovascularisation.
(miosis), aqueous flare (turbid proteinacious fluid in the anterior chamber), hypopyon (accumulations of white inflammatory cells in the ventral aspect of the anterior chamber) and a low intraocular pressure, as measured by tonometry.
Deeper ulcers benefit from performing a culture and sensitivity test on a bacterial swab from the diseased area. This can provide very useful information allowing specific and appropriate antibiotic treatment to be given. However, the results take two-to-five days. Some laboratories will perform sensitivity testing with antibiotics which are not available as ophthalmic preparations, while not including the few that are. A more rapid test which is easily performed, but frequently forgotten, is cytology. A scraping is taken from the edge of the lesion using the blunt end of a scalpel blade or using a cytobrush. The harvested cells are smeared onto a clean microscope slide and air-dried. They may then be Figure 6: A large superficial corneal ulcer with no corneal neovascularisation
stained with Dif Quik stain and examined immediately. The Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 820 24/11/2009 12:44:38 The typical histology of this type of corneal ulcer is shown
in Figure 7. Stromal ulcers may have a crater-like appearance
with fluorescein retention throughout. Descemetocoeles are deep craters with fluorescein retention in the walls; but no stain uptake at the base. The elastic Descemet's membrane may bulge forwards. Melting ulcers have varying depth to the ulcer but have a gelatinous appearance (Figure
8).
Figure 7: Ulcerative neutrophilic keratitis with poor epithelial adhesion at ulcer
margins, and anterior stromal necrosis in a 26-year-old Falabella.
Haematoxylin and Eosin. 100x magnification. Photo: Karen Dunn at FOCUS-
EyePathLab, North Kent Referrals, UK.
Figure 9: Sub-palpebral lavage system in place, exiting from the lower eyelid,
to treat a corneal ulcer: there is fluorescein uptake in the cornea.
lavage system (Figure 9) is invaluable. A factsheet about
applying these systems is available on www.eyevet.ie/
vet-information/tips. Note that there are very limited
ophthalmic medications licensed for use in food-producing
horses in Ireland. In situations where there is a threat to
sight or comfort of the animal, the Cascade system or
Essential Substances List may be employed. Be aware that
Figure 8: A melting ulcer in the dorsal cornea with fibrovascular reaction from
this can have implications for the horse's status regarding the limbus.
the food-chain. Corneal ulcers must never be treated with steroids, either topically or systemically. Steroids CurrENt rECoMMENDAtIoNS for
can rapidly deteriorate an ulcer into a melting ulcer or The aims of treatment are to relieve pain, to stop If the cause of the corneal ulcer or complication factors are progression of the corneal ulcer, to encourage corneal identified, treatment is targeted to bring about the most healing in a manner which minimises long-term scarring effective healing. Examples of complicating factors include and to eliminate secondary uveitis. These aims may be bacterial infection, stromal abscess (Figure 10), fungal
achieved medically, surgically or by a combination of the infection (Figure 11), eyelid abnormalities such as entropion,
two, and each case and the surrounding circumstances are aberrant hairs, presence of foreign bodies, trauma from the foot-plate of an in-dwelling sub-palpebral lavage In order for medical treatment to work, the horse will need system, local swellings and deficiency in tear production. to be compliant and the owner will need to be committed. Fortunately for us, fungal infection is very uncommon If the horse is not compliant, the use of a sub-palpebral in Ireland, although it is a frequent problem in warmer Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 821 24/11/2009 12:44:46 climates.
Simple and non-complicated ulcers: • Broad spectrum topical antibiotic ointment is • Topical Atropine 1% as a single application or once daily for three days; • Systemic flunixin meglumide 1 mg/kg twice daily for three-to-five days; and, Re-examine in three-to-five days, at which time the ulcer is expected to have fully healed, in that there should no longer be any fluorescein up-take. If it has not healed, consider complicating factors discussed earlier, perform cytology and culture and sensitivity tests.
Superficial erosions with epithelial under-running (SCCED): Figure 10: A yellow focus (stromal abscess) in the lateral corneal stroma with
• Corneal debridment under topical anaesthesia; significant uveitis (miosis, aqueous flare, fibrin in the anterior chamber) over
• A grid or punctuate keratotomy may be considered which the epithelium has re-grown, but the stromal abscess remains and
(Figure 12);
requires urgent treatment.
• Broad spectrum topical antibiotic ointment;• Topical Atropine 1% at time of debridement and then, to effect, to maintain a dilated pupil; • Systemic flunixin meglumide 1 mg/kg twice daily for three-to-five days; and, • Unless the owner notices problems, the eye re-examined in seven-to-10 days. These ulcers can persist, and stubborn non-healing ulcers should be referred.
Deep stromal ulcers (Figure 3) and melting ulcers (liquifactive
stromal necrosis, (Figure 8):
l
In-dwelling, sub-palpebral lavage system is Bacteriology swab for culture and sensitivity; Corneal cytology to assess whether there are rods (likely Gram-negative Pseudomonas aeruginosa), cocci (likely Gram-positive Staphyloccus spp. or Figure 11: PAS stain of the superficial cornea showing epithelial ulceration and
Streptococcus spp.), or fungi (which is uncommon fungal hyphae in the anterior stroma. Photo: Karen Dunn at EyePathLab, North
in Ireland), therefore, allowing the choice of the most Kent Referrals, UK.
appropriate topical antibiotic. A mixed infection is also possible. Contrary to popular belief, not all melting ulcers are infected with Pseudomonas spp. Some melting ulcers are sterile, with no pathogenic bacteria isolated; Topical antibiotics: The frequency of application varies depending on the seriousness of the condition. Hourly treatment is occasionally required in the presence of a melting ulcer.
Genticin (Roche) contains gentamicin 0.3% and this antibiotic has a good spectrum against gram negative bacteria, notably Pseudomonas aeruginosa. Unfortunately, its overuse as a first line antibiotic for a range of ocular problems has caused an increase in resistance among Pseudomonas organisms. This may be overcome by very frequent medication (every one-to-two hours) or fortifying the solution with injectable gentamicin. Figure 12: The appearance of a cornea 10 days after grid keratotomy for a
Exocin and Ciloxan are topical fluoroquinolones superficial corneal ulcer. The corneal ulcer has now completely healed, and the
with a broad spectrum of activity and are grid keratotomy significantly reduced after one month.
Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 822 24/11/2009 12:44:51 Chloramphenicol is a topical antibiotic which is very useful for broad-spectrum therapy.
Collagenolysis prevention to restrict the action of destructive enzymes is very important, and may be achieved through: Autologous serum prepared from 10 ml of blood in plain tubes, which is centrifuged after clotting and placed in an eye dropper bottle. This is then stored in the fridge and should be replaced in three-to-five days. It is applied at the same frequency as the antibiotic drops, for example every hour for serious melting or deep ulcers, or three to four times daily for less severe stromal ulcers.
Topical Acetylcysteine 5% (I-lube, Alcon).
Topical EDTA 0.2-1%.
Figure 13: Conjunctival pedicle graft three weeks after surgery in the
Oral tetracycline / doxycycline antibiotics – Thoroughbred horse featured in Figure 9.
Engemycin injection (Intervet) or oral oxytetracycline antibiotics (Vibroxy 100 mg capsules) 10 mg/kg overwhelming inflammation (endophthalmitis) occurs in the Uveitis control to minimise harmful sequelae: Atropine 1% may be used topically up to three times daily, used to effect and then only as often as is required to maintain a dilated pupil. Caution Signs of improvement include elimination of the signs should be exercised as systemic absorption of this of ocular pain (blepharospasm and ocular discharge) drug can reduce gut motility and, therefore, cause colic. Monitoring for signs of colic is thus Systemic NSAIDs such as phenylbutazone (4.4 mg/kg twice daily per os) or flunixin meglumide (the author's preference) at 1mg/kg twice daily I/V or per os will reduce the uveitis.
SurgICAL trEAtMENt
Surgery should be considered in cases where the
ulcer is deep or melting, for corneal perforations,
with or without iris prolapse, and in the case of a
descemetocoele. The aims of surgery are to fill the
deficit, thus creating a stronger repair, and to provide
blood vessels to the diseased area which will promote
healing and help arrest collagenolysis. Conjunctival
grafts are very useful as they are readily available and
have a high rate of success, although they do cause
some long-term corneal scarring. Conjunctival grafts
may be pedicle, free island, advancement hood, bridge
or 360º. They are left in place for six-to-eight weeks. The
most commonly used graft is a rotational conjunctival
pedicle graft, whereby a flap of thin conjunctiva is raised
from the paralimbal area and sutured into the deficit
with 6/0 to 8/0 absorbable suture material (Figure 13).
Amniotic membrane transplants are gaining popularity,
and may be commercially available coated in equine
limbal stem cells in the near future. This may reduce
protease effects and reduce corneal scarring.
Enucleation is required in cases where corneal rupture
cannot be repaired causing considerable pain and
discomfort; when secondary glaucoma develops
which is unresponsive to treatment; or, if infection or
Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 823 24/11/2009 12:44:53 and a reduction in the depth and extent of the ProgNoSIS for rECoVEry
corneal ulcer. Fluorescein is an invaluable test All corneal ulcers have the potential to deepen and perforate the for monitoring the progression of the healing globe (Figure 2), which leads to loss of sight and would possibly
process. Photography is a very useful tool which is, require enucleation. Other potential outcomes include phthisis nowadays, easily accessible. Digital cameras are bulbi (blindness and shrinkage of the eye) or blindness due capable of taking high resolution photos and using to scarring, cataract formation or secondary glaucoma. Less the macro function can improve the quality of close- serious, but undesirable outcomes include corneal scarring and up pictures. This is a good way of monitoring the permanent anterior or posterior synechiae. However, the fate of changes which occur over time and may be used as the case rests in the hands of the owner seeking timely urgent part of the case notes. veterinary attention and complying with the treatment plan, and The ideal time for the first re-evaluation of the case also in the veterinary care provided with a thorough examination, depends on the seriousness of the presenting appropriate diagnostic tests and treatment.
signs. Deep or melting corneal ulcers should be examined the next day. Superficial ulcers which were debrided are generally not checked for seven • Equine Ophthalmology. Brian C Gilger. Elsevier Saunders. days. Signs of insufficient healing to look out for ISBN 0-7216-0522-2.
include any deepening of the corneal ulcer, stromal • Equine Ophthalmology: An Atlas and Text Second Edition. malacia at the edges, worsening anterior uveitis KC Barnett, SM Crispin, AG Matthews. Saunders. ISBN (pupil remaining constricted, posterior synechiae, aqueous flare and hypopyon) and the lack of any • Ophthalmology for the Equine Practitioner. Dennis E Brooks. blood vessel response within the cornea.
Teton NewMedia. ISBN 189344151-2.
conTinuing EducaTion: quEsTions and ansWErs 1. ThE folloWing TEchniquEs arE usEful 4. mElTing cornEal ulcErs should bE WhEn Examining a dEEp cornEal ulcEr: a. retrobulbar nerve block a. Topical antibiotic and steroid in combination with b. auriculopalpebral and supraorbital nerve block systemic nsaid and antibiotics.
C. A Schirmer tear test to check for insuffi cient tears b. Topical antibiotic, mydriatic and serum with d. vision assessment using plr systemic steroids and antibiotics.
c. Topical antibiotic, mydriatic and serum with 2. supErficial cornEal ulcErs WiTh EpiThE- systemic nsaid and antibiotics.
lial undEr-running rEquirE: d. grid keratotomy followed by topical antibiotic, a. debridement and grid keratotomy with topical anti mydriatic and serum with systemic nsaid and biotics and mydriatics, possibly repeated in 10 antibiotics.
b. conjunctival pedicle graft with topical antibiotics 5. cornEal ulcEraTion may causE: and mydriatics.
A. Refl ex uveitis c. debridement and grid keratotomy every three days, b. glaucoma with topical antibiotics and mydriatics.
c. globe rupture d. Topical serum and mydriatics, with oral d. all of the above doxycycline.
3. Which of ThE folloWing sTaTEmEnTs is TruE rEgarding dEscEmETocoElEs? A. Descemet's membrane uptakes fl uroescein stain.
b. descemetocoeles are best treated medically.
c. descemetocoeles require debridement and grid keratotomy.
d. surgical repair should be considered for descem Irish Veterinary Journal Volume 62 Number 12
Irish Veterinary Journal Volume 62 Number 12
IVJ Dec 2009.indd 824 24/11/2009 12:44:55

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