The eyelids perform an integral role in maintaining the health of the ocular surface. Fundamental to this role is the perfect apposition that normal eyelids maintain with the globe. Disruption of this apposition will lead to ocular surface problems if not treated appropriately.
Eyelid lacerations are typically caused by sharp trauma and result in a full-thickness tear in the eyelid. It is extremely rare for any portion of the eyelid to be removed by the trauma. However, because of extensive swelling, it may seem that there are portions missing. If the laceration presents as an acute event, it should be surgically repaired immediately, as prolonging repair may result in devitalization of tissues.
If the wound is already very old and the tissue is already extensively devitalized, the globe should be protected with topical ophthalmic antibiotic ointment, and the eyelid should be allowed to heal by second intention. Once everything heals, reconstructive surgery to restore a functional eyelid can be performed.
The goal of surgical repair is to return the eyelid to exactly the same conformation as before the trauma. The extensive vascularization and blood supply to the eyelids will result in survival of all but the most devitalized of tissues. Unless the tissue is completely devitalized, it should not be resected. Even dangling pedicles should be kept and sutured into their original position. The edges of the laceration need only be cleaned, but should not be "freshened" by removing tissue. Even though the swelling may make it appear that there are portions of the eyelid that are missing, this is rarely the case. Holding the edges of the eyelid margin together will usually make this clearer.
Full-thickness lacerations should be closed in two layers. Simple interrupted sutures are used to appose the tissue between the skin and the conjunctiva (the muscle and tarsal layers), making sure no sutures go deeper than the conjunctiva. The skin is then closed by first placing a figure-of-eight suture at the eyelid margin. Then simple interrupted sutures are placed to close the rest of the skin. It is of utmost importance that the figure-of-eight suture be placed appropriately and that the eyelid margins be realigned exactly. If this is not achieved, the repair could result in entropion, sutures rubbing on the cornea, or the eyelid margin healing with a notch defect, which could then result in an unhealthy ocular surface. My suture of choice for this repair is 4-0 to 6-0 Vicryl.
Third Eyelid and Conjunctival Lacerations
Conjunctival lacerations typically do not need to be repaired surgically, as they will very rapidly by epithelialization on their own. Lacerations of the third eyelid, if they result in exposure of the cartilage of the third eyelid, should be sutured, making sure suture placement does not result in sutures rubbing on the cornea.
Trauma to the cornea typically results in either a superficial ulcer or a full-thickness corneal laceration. It is very unusual for trauma to cause a midstromal ulcer. Midstromal ulcers or descemetoceles are much more likely to be secondary to infection.
By far the most common ocular injury, a superficial corneal ulcer is one in which only the epithelium has been scraped off the underlying stroma. The epithelium has a very rapid healing mechanism that will result in complete re-epithelialization within 1–3 days, depending on the size of the ulcer. As long as the stroma does not get infected, the eye will heal itself. These ulcers do not have any appreciable depth and many times can only be detected by staining them with fluorescein. Treatment of an uncomplicated superficial ulcer is aimed at preventing infection and controlling pain. The first goal is best accomplished by applying a topical broad-spectrum antibiotic (3–4 x day; more often may slow healing). The pain is most effectively controlled by topical atropine (1–2 x day).
Lacerations of the cornea are most commonly caused by cat claws, although any other sharp object can cause them. As the size of the laceration increases, the likelihood of retaining vision decreases. Hyphema or a laceration that extends beyond the limbus is a poor prognostic factor. Because there is such a short distance between the cornea and the front of the lens, another important consideration - even when the laceration is small and the eye is clear - is the integrity of the lens. If the lens capsule is damaged, exposure of the lens material to the immune system may result in catastrophic uveitis.
If there is a chance to retain vision, the corneal laceration should be closed primarily. Closure is achieved by placing simple interrupted sutures of 7-0 to 9-0 absorbable or nonabsorbable material. The sutures should be mid- to two-thirds stromal depth but not enter the anterior chamber. If there is iris tissue protruding through the incision, it should be replaced as long as the laceration is less than 12 h old. If the iris tissue has been entrapped for longer, it should be resected. If the lens capsule is damaged, then removal of the lens material may be needed to prevent catastrophic inflammation, unless the lens capsule defect is very small - in which case it may seal spontaneously. As both of these procedures are best performed under an operating microscope and with training in microsurgical techniques, referral of these cases to a specialist should be considered. After surgery, eyes should be treated with topical and oral antibiotics as well as mydriatics.
If there is no chance for vision, enucleation is usually indicated.
Proptosis results from traumatic forces pushing the globe anteriorly to the point where the eyelids rest behind the globe's equator. The amount of force necessary for proptosis varies based on cranial conformation. Brachycephalic dogs require very little force, while dolichocephalic dogs require a lot. As the globe is pushed forward, extraocular muscles may tear and the optic nerve may be damaged. Once the globe's equator is anterior to the eyelid margin, it becomes entrapped in that position. The pressure of the eyelids on the globe cuts off the venous return, and the conjunctiva anterior to the eyelids begins to swell, making it even harder for the globe to go back to its original position. Because the eyelids can no longer lubricate the corneal surface, it begins to desiccate. Surgical treatment should be performed at once.
The prognosis for vision is low. The majority of proptosed eyes become blind. If there is no vision on presentation, then most likely they will not regain vision.
Not all proptosed eyes should be replaced. The blood supply to the inside of the eye travels alongside the extraocular muscles. If too much of the vasculature is compromised, the globe will undergo avascular necrosis. Proptosis in which there are three or more torn extraocular muscles should be enucleated. The most common muscle to be torn is the medial rectus. Therefore, the most common abnormality after globe replacement is lateral strabismus unless the muscle is surgically reattached. Proptoses in which the globe is ruptured should be enucleated. Proptosed globes that have hyphema may be replaced, but may become phthisical and require enucleation later.
Surgical replacement of a proptosed globe is fairly simple. The easiest way to bring the eyelids back in front of the globe where they belong is to perform a lateral canthotomy. Once the palpebral fissure is larger than the globe, the eyelids can usually be brought to their normal position fairly easily. A complete temporary tarsorrhaphy should be performed after replacement. If there is extreme swelling and hemorrhage behind the globe, it may be necessary to preplace the sutures for the temporary tarsorrhaphy and then, using a scalpel handle to shield the globe, tighten the sutures as the globe is pushed back into the orbit. Stents should be used to distribute the tension of the sutures on the eyelids. The lateral canthotomy is repaired with simple interrupted sutures, and the tarsorrhaphy is left in place for at least 2 weeks to allow the swelling to go down.
Blunt trauma results in globe rupture only with extreme force. Often this type of trauma leads to irreparable damage within the eye that makes visual recovery impossible. The most common clinical signs seen after this type of trauma are hyphema, subconjunctival hemorrhage, and conjunctival and eyelid swelling. Additionally, these globes show no signs of vision, lacking a menace response or a consensual pupillary light reflex. The most common place for globe ruptures to occur in small animals is at the posterior pole. As such, it is usually not possible to visualize the rupture without the aid of ultrasonography. Indistinct scleral borders on ultrasound along with signs of intraocular hemorrhage on ultrasound help confirm the diagnosis. Though visual recovery is unusual in almost all cases, some cases may heal to the point of having a comfortable eye. However, for most cases, enucleation is the treatment of choice.
Trauma-Induced Anterior Uveitis
Sometimes trauma to the globe doesn't result in an overt rupture or a laceration but still causes bleeding or inflammation within the eye. In these cases, the cardinal signs of anterior uveitis will be present (aqueous humor flare, hyphema, miosis, reduced intraocular pressure, etc.) after a traumatic event. This inflammation should be treated with topical steroids and atropine until complete resolution.
Corneal foreign bodies may range from small plant seeds that become adhered to the corneal surface and can be remove by aggressive flushing, to thorns or other sharp fragments that completely penetrate the cornea. Corneal foreign bodies should be removed and the resulting defect closed as for a corneal laceration. As with corneal lacerations, an important prognostic factor is the integrity of the lens.
Most conjunctival foreign bodies can be removed under topical anesthesia. The remaining conjunctival defect does not need to be closed surgically unless it is very large (> 1 cm in diameter).
Intraocular foreign bodies may or may not need to be removed based on the reactivity of the material and their location. Plant foreign bodies are very reactive, and if there is any chance of preserving vision, removal should be attempted. Metal foreign bodies may be very reactive (copper or iron) or relatively inert (gold, lead, plastic, glass, etc.). If the foreign body is inert and located in the posterior segment, removal may result in more damage than good. Diagnosis of the foreign body may be very difficult if the ocular medium is opaque and there is not a clear history. Radiographs, ultrasound, MRI, or CT or a combination of these modalities may be necessary in order to determine the location and nature of the foreign body. The foreign bodies themselves may result in permanent visual loss, or subsequent damage from disruption of the lens capsule or endophthalmitis (septic or sterile) may also result in visual compromise. Because of the many factors involved in determining the prognosis and most appropriate treatment plan, referral to a specialist should be considered in these cases.