17 Nov 2014
Cat scratch injuries leading to corneal lacerations are common in dogs and cats. These injuries can occur at any time of a dog’s life, but the risk is very much increased – and the damage often more severe – in puppies.
Apart from the fearless approach to cats young dogs usually show, they also have not developed a menace response yet. This protective blink of the eye in response to visual or tactile stimulation is a learned response that takes up to three months to develop. Before that, the eyes are far more susceptible to injuries. Brachycephalic dogs have more exposed eyes, which make them also more susceptible to injury.
The injured animal is usually uncomfortable and shows signs of ocular pain such as blepharospasm, excessive lacrimation and third eyelid protrusion. To facilitate a more thorough examination and provide pain relief for the patient, it is useful to apply a topical anaesthetic.
Gentle handling of the patient is necessary as even mild pressure to the eye could dislodge potentially delicate fibrin plugs sealing the wound, causing it to open and resulting in leakage of aqueous humour. Sedation or general anaesthesia may be considered for uncooperative patients to allow a thorough examination.
A Schirmer tear test (STT) should only be performed if a perforating corneal wound can be ruled out and it may be more appropriate to deal with the traumatic injury first and measure the STT at a re-examination appointment to rule out a low tear production, which may interfere with corneal healing.
Every patient with scratch marks on the face, eyelids or third eyelid should be carefully assessed for corneal involvement. Similarly, patients with corneal laceration should have all the adnexal structures examined to investigate the full extent of the injuries.
Any corneal injury is assessed for depth (superficial, deep stromal and perforating) and extent. A laceration adjacent to the limbus may extend peripherally to involve the sclera and the conjunctiva can sometimes obscure the extent of the lesion and may have to be removed to visualise the full extent of the lesion.
Corneal oedema often develops adjacent to the site of penetration. This will result in the edges of the cornea being thickened, which may make the depth of the laceration difficult to assess. A small corneal injury can self-seal with aqueous and fibrin or an iris prolapse, larger lesions may leak aqueous humour. The latter are usually more painful.
A fluorescein test may help to visualise smaller lesions; however, most corneal lacerations are visible without it and the benefits of a fluorescein test of making corneal defects easier to see has to be weighed against the potential risks of additional manipulation of these often very fragile globes.
Fluorescein dye is, however, very useful to perform a Seidel test, which is used to assess whether a corneal wound is leaking. A drop of fluorescein is applied to the cornea and is not flushed out as is done as part of a routine fluorescein test. In case of leakage the aqueous humour becomes visible as a small light green rivulet emerging from the wound through the highly concentrated orange dye on the corneal surface.
The anterior chamber is assessed for depth and content. It may appear shallower if the globe is ruptured and aqueous humour has leaked out of the eye. The anterior chamber normally contains clear aqueous humour, but following a sharp injury to the globe, it may contain blood (hyphaema), fibrin, purulent material (hypopyon) and, if the anterior lens capsule has been injured, lens material.
Hyphaema may occur due to the rapid change in intraocular pressure, or a trauma to the iris or posterior uvea (Figure 1). The pupil is assessed with regards to its shape and size relative to the unaffected pupil. The pupil may be distorted (dyscoric) if there is an iris prolapse (Figure 2). An iris prolapse usually presents as a round mass on the ocular surface in the colour of the iris or may be covered with an aqueous and fibrin clot, which is visible as a mucoid brown or grey material. This should not be disrupted during the eye examination.
The pupil in the injured patient usually constricts immediately after the injury, but should be dilated to examine the lens as well as to prevent adhesions between the iris and the lens (posterior synechia) due to the inflammation. Different mydriatics can be used to dilate the pupil. Tropicamide (0.5 per cent to one per cent) or atropine (0.5 per cent) eye drops may be used. The latter is often required to achieve mydriasis in a very inflamed eye, as an inflamed iris responds more slowly to these drugs and repeated applications may be necessary.
In patients with an iris prolapse the pupil should only be dilated if microsurgical facilities are present as in rare cases, an iris prolapse may dislodge when mydriasis is induced, resulting in leakage of the eye, making an urgent surgical intervention necessary.
Assessing the anterior lens capsule for an injury is essential in all patients following a penetrating injury to the eye. Very small penetrations or superficial scratches on the anterior lens capsule can self-seal, although this usually results in a small cataract at the site of the injury. Larger rents may lead to the exposure of lens protein to the eye and result in an often severe phacoclastic uveitis that may develop within hours of the injury, but in some cases, may not be appreciated until days after the event1,2,3 (Figure 3).
Ultrasonography is a valuable tool to assess the damage to the eye when the visual axis is not clear and the posterior segment cannot be examined, for example due to hyphaema, corneal oedema or cataract formation.
This diagnostic tool should be reserved for use by specialists if a perforating injury is suspected, as the mechanical manipulation of the eye may cause further damage in inexperienced hands or may result in leakage of an unstable eye that may then require urgent surgical repair.
After careful assessment, a decision can be made as to whether medical treatment or surgical repair is warranted. Small (less than 2mm) self-sealed perforations and superficial lacerations do not often require surgical repair. Provided there is also a formed anterior chamber, no iris prolapse and reasonable patient comfort, such injuries can be treated medically.
In cases where there is a corneal flap, this can be trimmed off by a specialist, if the deficit is shallow (less than one third of the thickness of the cornea) and afterwards, the patient can be treated medically. The following medical treatment can be considered.
As cat claws may harbour harmful bacteria – which can be introduced into both the cornea and eye – appropriate antibiotic choices include chloramphenicol or ofloxacin, which penetrate the cornea well.
To relieve a ciliary spasm and keep the pupil dilated, atropine one per cent should be applied to effect to maintain a dilated pupil.
Atropine should not be used if there is significant dry eye, if the intraocular pressure is raised, or in very small or debilitated patients, as systemic absorption can cause tachycardia and drying of bronchial secretions. Alternatively, tropicamide eye drops may be given at a higher frequency.
Systemic NSAIDs will provide pain relief and reduce intraocular inflammation.
Systemic broad-spectrum antibiotics should be added in case of a perforating injury.
A buster (Elizabethan) collar should be used to prevent self-trauma.
The patient should be rested and not be allowed to swim until wound healing is completed.
Surgical repair, thus referral to an ophthalmologist, is indicated in the following circumstances:
• non-perforating corneal wound where the superficial edges are gaping or a corneal flap is present;
• deep corneal lacerations – that is, greater or equal to half of the corneal depth;
• perforating corneal wounds; and
Surgical treatment requires specialist equipment and expertise. Procedures may include the removal of a corneal flap or suturing of an unstable corneal wound with or without grafting procedures.
Precise suture placement is achieved using magnification, microsurgical instrumentation and techniques, and fine suture material. In case of an iris prolapse, replacement with or without partial resection of the iris tissue may be necessary (Figures 4 and 5). In case of a lens injury, removal of the lens via phacoemulsification may be necessary to prevent or treat a lens-induced uveitis.
Extensive intraocular damage, as well as financial restraints, may prevent the surgical repair in some patients. Therefore, enucleation of the damaged eye occasionally provides a humane alternative.
Complications following intraocular surgery may occur months to years following the injury, including secondary glaucoma and retinal detachment, making regular monitoring of patients necessary to recognise and treat such complications effectively.
Lens traumata in cats have been associated with the development of a malignant and often life-threatening intraocular sarcoma several years post-injury, and therefore close monitoring – and in some patients, early enucleation – may be considered in this species, particularly if eyes are not visual.
The prognosis for the eye and vision very much depends on the extent of the injury. In general, there is a better prognosis for non-penetrating corneal wounds. Perforating injuries always have the risk of an endophthalmitis due to bacterial or fungal infections, even though these complications are rare6.
Cat claw injuries to the eye are relatively common. Gentle patient handling is required with an immediate thorough assessment of the damage sustained. General anaesthesia may be helpful in these often very painful patients.
Superficial corneal lacerations, without an apparent corneal flap, may heal uneventfully when treated like a corneal ulcer. Deep and full-thickness lacerations usually require surgical repair by primary closure or using different grafting procedures.
Rupture of the lens requires urgent lens removal via phacoemulsification to avoid an often blinding phacoclastic uveitis.
Owner education appears essential when trying to avoid these often severe injuries to the eye. Puppies should not be left to play with cats, at least during the first three months of their lives.
• Please note some drugs mentioned in this article are not licensed for use in dogs and cats and are used under the cascade.
Figure 1. The right eye of a two-year-old Chihuahua following a cat scratch injury. Note the corneal laceration and the hyphaema.
Figure 2. A 12-week-old Labrador retriever puppy with a perforating corneal wound with iris prolapse. The brown round lesion in the dorsolateral aspect is the iris tissue covered by a layer of fibrin. There is some corneal oedema surrounding the lesion. The iris prolapse is further emphasised by the distorted iris (dyscoria) towards the lesion. A small amount of fibrin and blood are found in the anterior chamber.
Figure 3. A springer spaniel following a penetrating injury and lens trauma that has developed a phacoclastic uveitis and secondary glaucoma (3a). This eye also had a retinal detachment and was enlarged only four days after the initial injury (3b). The globe was enucleated.
Figure 4. The same puppy as in Figure 1 after surgical repair of the corneal wound. Partial resection of the iris was required in this patient. Following the direct suture of the cornea with 9/0 Vicryl, a special bandage contact lens (marked with black dots to make it easier to recognise) and a temporary tarsorrhaphy were placed to protect the eye during the healing process.
Figure 5. The same puppy as Figure 1 two weeks following the procedure. The corneal wound is healed and corneal vascularisation of the area is slowly regressing. The pupil is slightly dyscoric due to the partial iris resection. There is no evidence of lens involvement. The pupil is still dilated following the administration of atropine eye drops. The long-term prognosis for this eye and vision is excellent.
