Corneal Ulcers are a very common and painful pathology in the veterinary practice, with many variations in terms of clinical presentation and treatment. This disorder consists mainly on a corneal lesion that may or may not extend to deeper layers of the eye, and can be caused by trauma, foreign objects, chronic and/or chemical irritation, neuropathies, autoimmune diseases, genetic predisposition, among others.
We have already touched on how PRP can be used to help corneal ulcers in horses. Now we look at this form of treatments for dogs & cats.
The cornea is the outer layer of the eye, which acts as a mechanical barrier between the eye content and the environment. This layer should normally be transparent, since there are no blood vessels or pigments on it, therefore, any changes on the appearance of the cornea should be immediately examined by a veterinarian, so that a definitive diagnosis and treatment can be performed and installed.
The effectiveness and quickness of the treatment are key to protect the corneal ulcer from infection, which could lead to uveitis and several other complications that can even end up in complete sight and/or eye loss.
Causes of Corneal Ulcers in Dogs or Cats
In the small animal practice, the most common causes for corneal ulcers are foreign objects or sharp trauma. However, competing for the first place on the statistics, genetics come to play an important role on the incidence of this disease, since there are particular dog and cat breeds that are more likely to develop it because of the skull structure and eye exposure.
All brachycephalic breeds (Bull Dog, Boston Terrier, Pug, Persian Cat, etc.) tend to develop elevated lacrimal evaporation, dry-eye syndrome, entropion, ectropion, ectopic cilium, trichiasis, districhiasis and other typical conditions that can chronically irritate or generate a lack of corneal lubrication, leading to rupture of the corneal epithelium and damage of the stroma, descemet and sometimes even the endothelium.
Other diseases that can set the table for corneal ulcers are diabetes mellitus, ehrlichiosis, autoimmune conditions, hypertension disorders, self-inflicted injury due to behavior alterations, and in very rare cases even parasites, such as Dirofilaria spp.
When injured, the epithelium cells tend to heal quickly by accelerated migration and mitosis, repairing the lesion in 4 to 7 days.
When the stroma is involved, the healing might be more complicated and can take a few weeks, since collagen needs to be synthetized to leave a permanent scar. If the endothelium is damaged, it is very likely that there will be a persistent edema, since the endothelial cells are not capable to perform mitosis and the tissue repair lies exclusively on the mobility of the adjacent cells towards the injured area.
Generally, the pet owner will consult their pet for irritation, red and swollen eyes, excessive or oddly colored tearing, blepharospasm, cloudy eye appearance, focal or multifocal dull or blue spots, face rubbing with paws or ground, and in extreme cases, purulent or bloody discharge from the eyes.
Something that can orientate the veterinarian on the chronicity of the ulcer is that acute ulcers are much more painful than the chronic ones; this happens because the corneal epithelium has an outstanding number of cilliary trigeminal nerve branches that lose myelin as they go deeper into the eye structures, making the epithelium more sensitive than the endothelium. Hence, injuries involving solely the epithelium tend to cause a more desperate pain than the ones that already penetrated into de stroma, descement and endothelium.
Diagnosis, Classification and Conventional Therapy
The diagnosis of corneal ulcers is easily performed by the animal health professionals, and can be summarized in a few basics:
- Physical examination. Ophthalmic and neurologic examination will be performed to evaluate intraocular pressure, pupil response, etc.
- Schirmer Test. The veterinarian will measure the tear production to know if the ulcer could be secondary to dry-eye syndrome or other aqueous tear production disorders.
- Fluorescein dye. The veterinarian will apply a fluorescein solution directly into the eye surface. Since the cornea is hydrophobic and the stroma is hydrophilic, the fluorescein will adhere only to the exposed stroma, where the corneal damage is located. This will allow the evaluation of the injury, its extent, depth, exposed structures and classification.
- Culture. In cases of infected ulcers, samples should be taken from the peripheral area of the injury for laboratory culture.
There are several classifications for corneal ulcers, but from the clinical point of view, the most practical classification is the following:
Simple Corneal Ulcer
This type of ulcer involves only the epithelium, with no stromal damage whatsoever, and non-infected. It is usually acute presented and severely painful for the dog or cat. Small pupils, intraocular inflammation and corneal neovascularization can be appreciated in some cases.
If not diagnosed and treated rapidly, the exposure can become infected, which will produce proteases, collagen lysis and perforation. It is also important to provide constant vigilance of the patient and an elizabethan collar, since the pain may lead to self-injury.
The usual treatment for SCU includes topic vitamin A, topic and/or systemic NSAIDs (diclofenac, tramadol) and topic antibiotics.
Complicated Corneal Ulcer
A CCU is any ulcer involving deeper layers of the eye, such as the stroma, descemet and endothelium. An ulcer also should be considered as complicated if scarring has not occurred after 10 days of treatment for SCU.
Samples should always be taken for culture studies before applying any dye or medication. Within the CCUs, there are indolent ulcers, “melting” ulcers (collagen lysis that gives a jelly-like appearance), deep ulcers, descemetocele and corneal perforations. The chronology occurs as the stroma is destroyed, generating a rupture of the descemet membrane, then corneal perforation involving the endothelium, and finally, prolapse of the iris.
If the full chronology happens along with severe bacterial infection, the patient will most likely lose vision and/or the eye. Neovascularization, uveitis, edema and others will be manifested in a more severe way than with SCU.
Conventional treatments for CCU include specific topic antibiotics based on culture results, topic and/or systemic NSAIDs, topic atropine, and in many cases, temporary surgery is indicated.
Different surgical techniques may be used, but pedunculated conjuntival flaps and keratoplasty are the most common ones, since they keep lubrication and blood supply to the ulcer.
PRP Alternative for Corneal Ulcers
The Platelet-Rich Plasma contains serum, leucocytes and platelets, being these last ones the interest of the PRP Therapy. The growth factors contained inside the alpha granules of the platelets (such as platelet-derived growth factor (PDGF), transforming growth factor (TGF), platelet factor interleukin (IL), platelet-derived angiogenesis factor (PDAF), vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), insulin-like growth factor (IGF) and fibronectin) are released when the platelets become active, enabling all of their physiological functions, which regenerates lost tissue by stimulating cell differentiation and tissue morphogenesis.
This is incredibly important and different from the scarring process, since regeneration means that the function of the tissue is reinstalled, while scarred tissue covers the damaged area, but does not possess physiological activity.
PRP is especially useful in cases of corneal ulcers, since the main concern is the timing. If the installed treatment does not work fast, the consequences are irreversible. PRP therapy, along with the basic pain management and antibiotic medication, accelerates the healing process.
In cases of SCU, the clinical results are impressive, since pain is significantly reduced, and the epithelium cell mitosis happens much faster. For CCU cases, clinicians have reported less scarred tissue and adherences, faster recovery and lower rates of blindness secondary to perforation.
On top of this, inflammatory and/or allergic reactions are not an issue (as it may happen with other medication, or commercial serum from different species), since the PRP is an autologous preparation, which lowers the risk of secondary effects.
In fact, laboratory studies have been made in rabbits by Acosta, L. Castro M., Fernandez M., Oliveres E., Gomez-Demmel E., and Tartara L. in 2013, Argentina, where they artificially caused 10 mm deep corneal ulcers on each individual, and compared saline solution treatment every 8 hours for 7 days for the Control Group, commercial deproteinized veal blood extract gel treatment every 8 hours for 7 days for the Gel Group, and autologous PRP on day 1 and day 3 for the PRP Group.
The results showed that the Gel Group and the PRP Group had extremely similar results, which does nothing but emphasize the pros of using PRP therapy in the vet world: easy to obtain, easy to apply, effective and lower dosage needed.
These facts have a direct impact on the patient’s recovery, since PRP heals faster, requires less outlay and effort for the pet owner, and bothers the patient a lot less.
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