Corneal ulcers in pets - dogs and cats
What is a Corneal Ulcer?
The external eye is split into 3 distinct areas: the cornea; the limbus and the sclera. The cornea is the transparent 'window' of the external eye, the limbus is the narrow transition zone to the white sclera that makes up approximately 2/3 of the entire globe
A corneal erosion or ulcer is a defect that breaks the integrity of the cornea i.e. some part of it is 'missing' and at the site of the ulcer the cornea is 'thinner' than it should be at the site of the pathology. An erosion, classically, is more superficial compared to an ulcer, however for the purposes of this blog any defect assocaited with the cornea will be termed an ulcer
Why is a Corneal Ulcer a Problem?
The normal cornea is a thin structure (<1mm). Full thickness defect with eye rupture can therefore happen quickly as a progression from an initial defect or from direct trauma
The normal cornea is devoid of a blood supply. The lack of a blood supply is a requirement for transparency. Transparency is a key requirement for the cornea is to allow light to enter the internal eye and therefore act as an optical instrument
When the cornea is damaged, a reduction in transparency is the most common pathology. The cornea becomes opaque (cloudy), therefore the amount of light entering the eye is reduced and vision is decreased through the site of the opacity
Corneal ulcers, especially superficial ulcers, can be very painful. This pain leads to lid spasm and therefore marked reluctance to open the eye. This can make examination and treatment challenging
Without a direct blood supply, the normal healing processes can't occur. As a result corneal repair and healing is considerably slower compared to blood associated structures e.g. skin
The cornea is mostly composed of water and protein fibres (collagen). The collagen matrix structure is vulnerable to attack from chemicals that break-down protein e.g. protease enzymes. If the protein fibres are 'attacked' then the cornea will lose transparency. In addition, the structural relationship between the corneal fluid and fibres is crucial to the structures requirement for transparency. The transparent cornea has a regular, repeating arrangement of fibres and fluid. The size of the fibres and the fluid 'size' between the fibres are very similar. My analogy is that the normal arrangement is like a 'chess board'. The black represents the fibres, the white the fluid. If the cornea becomes water-logged (for any reason) this excess fluid disrupts the chess board arrangement. This changes it from an ordered into a dis-organised structure. When the cornea is dis-organised light doesn't pass through the cornea, but 'bounces back', typically causing the cornea to become 'cloudy'
If an ulcer forms, regardless of the cause, bacteria can more easily colonise the defect. Bacteria can release protease enzymes that will damage the collagen making the ulcer worse and further decrease transparency
Protease damage to the corneal collagen can also occur from non-bacterial causes. There are proteases that are persent: -
a. Within the corneal structure itself, termed matrix metallo-proteases (MMP's)
b. White blood cells and surface epithelial cells can release proteases
c. The normal anti-protease activity of the tear film can become over-whelmed
In other words damage to the cornea can lead to further damage to the cornea by the activation of protease enzymes resulting in a vicious cycle. Regardless of the source of the protease enzymes, enzyme activation leads to a chain of events known as melting. This causes the corneal ultra-structure to change from a well-ordered, strong transparent structure into a dis-organised liquefying, opaque 'soup'
How can a pet present with a Corneal Ulcer?
The initial clue to an owner of an eye problem is eye pain. Only very rarely to ulcers present when there are no apparent signs of eye pain e.g. following tick paralysis of the muscle responsible for lid closing
Eye pain manifests as: lid spasm leading to an increased blink rate or a narrower opening between the lids when comparing a painful eye with a 'normal' eye and increased tear production (if the eye can produce tears). In addition, the painful eye will be photophobic
How does a vet test for the presence of a Corneal Ulcer?
The most sensitive test of corneal integrity is Fluorescein staining and this is an excellent test
Fluorescein is a green dye that is touchec onto the cornea and then the dye is flushed away. Fluorescein will 'stick' to a defect in the corneal epithelium and indicate where it has been breached, indicating an ulcer. The most sensitive way to assess fluorescein staining is to view fluorescence that occurs when viewing with a 'blue' light
Ironically, a very deep corneal defect will not take up stain at 'the bottom' of the ulcer. This is because the basement membrane of the one-cell thick corneal endothelium (called Descemet's membrane) will not take up stain. These very deep ulcers are termed descematoceles and the eye is only 1 cell thickness from rupturing. These ulcers have stain that sticks to the 'walls' of the ulcer and not the the base. In normal light, without stain, paradoxically a descematocle base looks 'black'
Why are Brachycepahlic dogs (and cats) more prone to Corneal Ulceration?
Brachycephalic breeds of dog have a characteristic wide head and short nose. They include: Affenpinshcer; Brasileiro; Boston Terrier; Boxer; Brussels Griffon; Bulldog (English, American, Australian and French); Bullmastiff; Cane Corso; Cavalier King Charles Spaniel; Chihuahua; Chow Chow; Dogo Argentino; Dogue de Bordeaux; French Bulldog; Japanese Chin; Lhasa Apso; Mastiff; Neopolitan Mastiff; Newfoundland; Pekignese; Pug; Shar Pei; Shih Tzu; Staffordshire Bull Terrier and Tibetan Spaniel
Brachycephalic dog breeds generally have the 'illusion' of large eyes. This is achieved by selectively breeding for a shallow bony orbit that therefore results in the globe being further 'forwards' than it was originally intended to be. The 'forwards' position of the eye leads to lids that often don't fully meet over the globe and oftentimes during sleep the lids aren't closed. The forwards located eye means that the lids don't blink as frequently over the globe as they should. The result is that the tear film is often not distributed over the globe as often as it should (due to lower blink rate) and focal drying of the tear film (due to lids not meeting) leads to poor tear film coverage
'Big eyes' unfortunately leads to an increased risk of corneal ulceration from direct trauma and as a consequence of compromised tear film coverage
Brachycephalic dogs can often suffer from dry eye (either as a young dog with under-production of tears) or as a middle-aged dog due to the development of immune-mediated dry eye (see below)
Why is poor tear film often associated with the increased risk of developing Corneal Ulcers?
Tear film fulfills many important roles to the cornea: it helps protect the cornea from pathogens and abrasive agents; it provides a smooth surface for the efficient refraction of light. Tears also wash away surface corneal contamination
The most important job of the tear film is to provide the oxygen delivery mechanism to the cornea itself
Tear film is an exquisite multi-layered liquid, classically thought of consisting of three layers: mucus to cause it to 'stick' to the cornea; water (aqueous phase) and an outer covering of fat (lipid)
The aqueous phase allows atmospheric oxygen to 'dissolve' into it. The oxygenated aqueous phase of the tear film provides the oxygen delivery mechanism for the cornea. The mucus therefore anchors the tear film to cornea and the outer lipid layer lessens evaporative losses. Evolution has resulted in the production of tears to allow oxygen to diffuse from the aqueous phase onto the cornea
Therefore too low production of tears, poor distribution of tears, increased losses of tears all lead to increased risk that oxygen delivery to the cornea becomes compromised. This then leads to corneal pathology and is a huge risk-factor for the development of certain types of ulcer
Can pets get 'dry eye'?
The simple answer is 'Yes'
The most common form of dry eye occurs in middle-aged dogs and results from a likely immune-mediated destruction of their own tear glands
Typically, with a reduction in the aqueous phase of the tear film the eye 'reacts' producing more mucus and more fat, giving rise to a mucoid or mucoid/yellow discharge. Bacterial conjunctivitis can often cause a similar discharge and it is common (initially) for the treatment to consist of antibiotic drops or gel. If the eye is dry, this brings about an apparent improvement, but once the topical preparation runs out, the discharge returns. The reason (in this hypothetical instance) is that the reduction in the eye discharge wasn't because of the anti-bacterial component of the drops, but because a wetting agent was placed onto the cornea. Typically, with a bacterial conjunctivitis the situation will resolve with appropriate anti-bacterial topical medication and the discharge doesn't 'return' when the drops run-out
The Schirmer Tear Test (STT) involves placing a graduated, standardised strips of paper onto the lid so that the paper soaks up any available tears. The test is conducted over 60sec with the following categories: readings of 10mm or < 10mm are diagnostic for dry eye; readings of 11 - 14mm are diagnostic for sub-optimal tear levels and readings of 15mm or > 15mm (in a non-painful eye) are considered 'normal'
The diagnosis of 'immune mediated dry eye' is made by excluding other causes of dry eye. This is done by: -
Checking that there is a normal nostril on the same side of the face as the 'dry eye'. If there is a 'normal' nostril, this excludes neurogenic dry eye. Neurogenic dry eye is a nerve interruption (palsy) to the tear gland and nasal mucosa leading to lack of tears and nasal secretion
The age-group is important in 'ruling out' immune-mediated dry eye. This is because young dogs only very rarely suffer from immune-mediated dry eye. Their most likely cause for dry eye is that they have been born with under-sized or under-functioning tear gland(s). This is termed lacrimal gland hypoplasia
Iatrogenic dry eye can occur with the use of: atropine eye drops; sulphasalazine or following certain surgeries
Cats can also suffer from dry eye, however their form of dry eye is usually secondary to feline herpesvirus (FHV-1) attack and subsequent scarring of the tear gland ductules. This scarring prevents the 'release' of tears from the tear glands, resulting in dry eye. Treatment is either frequent tear film supplementation or parotid duct transposition (PDT)
What are the treatment options for Dry Eye?
In short, this depends on the cause (aetiology) of the dry eye, but all forms require tear supplementation
In young dogs, there are 2 options: frequent tear supplementation or surgically transposing the parotid salivary gland duct from the mouth to the eye. This surgical procedure bathes the eye in saliva (known as parotid gland transposition - PDT)
70% of immune-mediated dry eye can respond (given time) to immuno-modulatory topical agents. There are 2 medications in this class of drug: cyclosporine and tacrolimus. OPTIMMUNE EYE OINTMENT is branded cyclosporine 0.2%. Administration of immuno-modulators is every (q) 12h (2x per day). The hope is that by 'blocking' the 'self-attack' the tear gland(s) will regenerate and normal tear production will be resumed. Treatment with immuno-modulators is required for life. As it takes time for the tear gland(s) to regenerate then tear supplementation should be started immediately on diagnosis of dry eye. Immune-mediated dry eye typically will occur at both eyes, although not necessarily at the same time and not the same extent
Neurogenic dry eye almost always affects 1 eye. Tear supplementation forms the basis of treatment, but in addition oral pilocarpine 1% drops can be used at a dose of 1 drop / 5kg bodyweight q 12h initially. Pilocarpine given orally has a direct affect on stimulating the damage nerve causing tears to be produced again (and the nasal crusting to stop). Unfortunately, signs of toxicity can develop before the pilocarpine exerts its stimulatory effect on the nerve. Common signs of toxicity are: dullness; depression; vomiting; diarrhoea and hyper-salivation. If tear stimulation occurs prior to toxicity then topical tear supplementation can be reduced. The cause for the damage to the nerve is often unclear, even with advanced imaging studies (MRI scan), however pressure on the nerve from a tumour, abscess or fungal granuloma remain other reasons
What tear supplementation options/preparations do I recommend for Dry Eye?
Human pharmacy bulk-buying power means that the purchasing of non-prescription tear supplementation agents is usually the most economical route for an owner
If an owner prefers an ointment preparation, I recommend carbomer gel e.g. VISCOTEARS / GEL TEARS etc
If an owner prefers a drop preparation, I recommend sodium hyaluronatge e.g. HYLO FORTE
How can Corneal Ulcers be Classified and how are the Different types Treated?
I classify ulcers on their likely response to treatment and put ulcers into 3 broad (and at times overlapping) categories. In addition there is a condition almost universally in the cat - the feline sequestrum, which will be presented at the end of this classification.
Category 1- Straightforwards Ulcers
These ulcers heal with supportive treatment (often topical and oral) in around 72h or <72h. Referral veterinary eye Dr don't see these ulcers as they are treated by primary care veterinary surgeons. These ulcers generally form the bulk of ulcer presentations
Category 2 - Non-healing Ulcers
Other names for these types of ulcer are: 'indolent', 'Boxer' or SCCED ulcers - Spontaneous Chronic Corneal Epithelial Defect
These ulcers that fail to heal within 72h
Characteristically these ulcers are superficial and involve the top-most 'layer' of the cornea (the epithelium)
These ulcers have areas of epithelium that are non-adherent to the next 'layer' (the epithelium basement membrane)
These types of ulcer result from a failure of healing
In my experience, only very rarely do these types of superficial ulcers become deeper 'eye threatening' stromal / melting or descematocele ulcers
There are 2 types of approach to treating the non-healing ulcers: conservative and surgical: -
Category 2 - Non-Healing Ulcers Conservative (non-surgical) approach: -
Conservative treatment involves symptomatically targeting the following areas: lessening the risk of bacterial complication by using antibiotics; decreasing the chances of the ulcer becoming deeper (oral doxycycline at 10mg/kg q 24h or 5mg/kg q 12h) and providing the 'building blocks' to allow the cells to anchor to their basement membrane - CLERAPLIQ drops every 48h
In my experience this gives a 20% chance of avoiding surgery
Category 2 - Non-Healing Ulcers Surgical approach: -
Surgical treatment for non-healing ulcers requires subtle trauma to the cornea to trigger repair. Indolent ulcers have areas of non-adherent epithelium and surgically I advocate superficial keratectomy to remove all of this outer superficial surface layer. I provide subtle surgical trauma via grid keratotomy to stimulate healing and then I place a third eyelid flap (TEF) over the corneal surface to act as a bandage and to reduce ocular pain. The TEF stays in place for 14-17d
Cost estimate for this surgery at PetVision is $1.4K + weight factor. The weight factor is a pet's weight in kg x 10 e.g. for a 22kg dog this would be 10x 22 = $220, therefore the total surgical cost would be $1400 + $220 = $1620
Diamond Burring: -
I do not use and therefore don't advocate the use of a 'diamond bur' in the surgical treatment of non-healing ulcers. In my experience these ulcers do not become deeper, yet I have seen the use of a 'diamond bur' transform this type of ulcer into a deeper, stromal ulcer requiring graft treatment to save the eye
Subtle surgical trauma to the anterior stroma in the cat: -
It is contra-indicated to perform techniques that cause subtle surgical trauma to the anterior stroma in the cat. This is because there is an increased association to the development of a sequestrum. This therefore forms an iatrogenic reason for sequestrum development
Category 3 - Stromal Ulcers
Other names for these types of ulcers are: melting ulcers; decematoceles and sight / eye threatening
Stromal ulcers can have various depths, but characteristically all go through the surface epithelium, the epithelial basement membrane and affect the middle corneal stroma. The cornea invariably becomes 'cloudy' or 'blue' and a visible defect can be seen
These ulcers are problematic and are often in a 'vicious cycle' where the ulcer will get deeper. Often, the end result without treatment, is corneal rupture and loss of the eye
These ulcers need prompt aggressive conservative treatment or referral for surgical intervention
There are 2 types of approach to treating these ulcers: conservative and surgical
Category 3 Ulcers - Conservative Treatment
This involves intensive (2 hourly) topical administration of topical antibiotics e.g. OCUFLOX (ofloxacin 0.3%) or CILOXAN (ciprofloxacin 0.3%) and TOBREX (tobramycin 0.3%) or TRICIN (triple antibiotic) in conjunction with autologous plasma in EDTA. I also recommed dilating the pupil with either MYDRIACYL (tropicamide 1% or 0.5% or topical atropine 1%. I advocate using oral doxycycline at 10mg/kg q 24h or 5mg/kg q 12h and oral non-steroidal anti-inflammatory (NSAID) to help lessen the risk of intra-ocular inflammation (uveitis) and to help lessen pain, thereby making it easier for the frequent topical dosing
A reasonable expectation for conservative management in the resolution of a stromal ulcer depends on the depth of the ulcer and the degree of corneal 'melting' but ranges in the 10 - 30% category. Unfortunately time frames often run into weeks. If there were a 'backwards' step when treating these ulcers conservatively, that would be a poor sign
Category 3 Ulcers - Surgical Treatment
Surgery involves the removal of the unhealthy cornea (keratectomy) and using grafts to stabilise the keratectomy site
There are 2 commonly available autologous grafting structures: conjunctiva from around the eye and peripheral cornea
The conjunctiva is fashioned into a pedicle graft (CPG) and then sutured into the keratectomy
An 'advancement graft' of cornea known as corneo-conjunctival transposition (CCT) carries a very high
The choice between the 2 graft materials depends on: the size, site, depth of the ulcer and if there is active melting
Surgical success rates for stromal ulcers, in my experience, are >95% i.e. the result is that the eye is visual and pain-free
Cost estimate for CPG surgery is $2500 + weight factor. The weight factor is a pet's weight in kg x 10 e.g. for a 22kg dog this would be 10x 22 = $220, therefore the total surgical cost would be $2500 + $220 = $2720. Cost estimate for CCT surgery is $3000 + weight factor e.g. for a 12kg dog this would be 10x 12 = $120, therefore the total surgical cost would be $3000 + $120 = $3120
Feline Sequestrum
A corneal sequestrum is a 'dead' area of cornea that presents as a brown or black lesion. It may or may not be associated with eye pain
A sequestrum can happen in any breed of cat, however the following are over-presented: Himalayan; Burmese; Siamese; Abyssinian and Persian
Risk factors for the development of corneal sequestration include: abrasion of the cornea from aberrant hairs; feline herpesvirus (FHV-1); dry eye and iatrogenic (vet induced) with the use of techniques to subtly damage the anterior stroma in the treatment of non-healing ulcers
If a cat develops a sequestrum in ine eye, there is a 30% chance a sequestrum will form at some stage in the opposite eye
'Self-cure' of sequestra can happen. Here the sequestrum becomes 'shed'. Typically blood vessels grow towards the black plaque and Matrix Metallo-Proteases (MMP's) become activated leading to shedding. Unfortunately, this process can also lead to eye pain and also a full thickness rupture. Shedding takes upwards of 12 months.
There are 2 types of approach to treating these ulcers: conservative and surgical: -
Sequestrum - Conservative Treatment
If there are no signs of eye pain, then conservative treatment with tear supplementation (see above) is appropriate, together with CLERAPLIQ. In my experience there is around a 20% chance that the eye will remain pain-free and eventually (> 12 months) the brown/black sequestrum will be 'shed' from the cornea i.e. self-cure
Sequestrum - Surgical Treatment
If there are any signs of eye pain, then surgical intervention would be the best alternative, due to the protracted time-frame for 'self-cure'. The sequestrum can be surgically excised (keratectomy) and the keratectomy site supported by a graft. This can either be a conjunctival pedicle graft (CPG) or corneo-conjunctival transposition (CCT)
Cost estimate for CPG is as follows: base-price $2400 + weight factor (10x cat's weight - kg) and for CCT is as follows: base-price $3000 + weight factor (10x cat's weight - kg)
At PetVision, if surgical intervention were required to treat a corneal ulcer (regardless of depth and severity) success rates are > 95% i.e.the result is a visual & pain-free eye.
I hope the above information proves to be both useful and practical, Doc Guy aka 'The Eye Guy' :)
Dr Guy Clare MA BVSc CertVOphthal
Dr Guy has over 20 years experience in solely treating pets (dogs and cats) eyes. Pets are brought from all over Queensland and interstate for his expert opinion and management. Routine appointments are scheduled Monday to Friday. In addition he is available for, emergency cases outside of normal hours. All cases need to have been assessed by a veterinary surgeon prior to arrival for an appointment. Referral from a veterinary surgeon can be either following written or verbal communication. Verbal referral can be made at T: 1300 EYE GUY (T: 1300 393 489). PetVision is on the web, please visit the Pet Vision website.
Dr Guy Clare is a UK Qualified veterinary ophthalmic surgeon (holding the Royal College of Veterinary Surgeons Certificate in Veterinary Ophthalmology - CertVOphthal). Prior to emigrating to Australia in 2009 he lectured in Ophthalmology at Liverpool University Veterinary School and ran a private ophthalmic clinic. In Australia he is recognised as a Consultant Practitioner in Veterinary Ophthalmology. He is based at PetVision on the Sunshine Coast in SE Queensland. PetVision is unique, dealing only with pet eye diseases, and is a veterinary husband and wife team. Dr Yvonne is in charge of patient anaesthetic protocol and anaesthetic delivery. It is very common for eye diseases to occur in older patients and brachycephalic breeds. Careful anaesthesia forms a vital component to PetVision practice successes.