Handling ocular emergencies (Proceedings)
Ocular emergencies are not commonly seen in general practice, but prompt recognition of the problem may allow for preservation of vision and/or the globe as a whole. This discussion will review five conditions that should be treated as an emergency and how to manage them properly.
A globe proptosis is a traumatic condition almost exclusive to brachycephalic breeds. The globe is forced forward and becomes trapped in front of the eyelids. These patients present with what appears as severe globe swelling and should not be mistaken for glaucoma. If the eye cannot be dealt with immediately, thick artificial tear ointment should be applied to the cornea to prevent it from drying out. With any proptosis, the chance of preserving vision is estimated at 20%. Signs that suggest a good prognosis for vision include a normal PLR and intraocular pressure, normal fundus exam, and lack of hyphema. Severe periocular inflammation, hyphema, retinal detachment, lack of PLR, and ruptured extraocular muscles all suggest a poor prognosis for preserving vision. Treatment involves rapid replacement of the globe under anesthesia and suturing the eyelids partially closed (tarsorrhaphy) until the swelling recedes. These patients are treated with topical antibiotic ointment, and oral antibiotics and steroids. The tarsorrhaphy sutures are removed at 2-3 weeks and assessment of the corneal surface and visual potential is made. Corneal ulcers are common with this condition as the cornea often dries out considerably before presentation. Lateral strabismus is also very common as the medial rectus muscle nearly always tears with a proptosis.
Acute glaucoma is a devastating disease that can strike very quickly. It involves a rapid increase in intraocular pressure as a result of decreased outflow of aqueous humor. I often use the analogy of a plugged drain to help people visualize the concept. Without treatment, permanent vision loss can occur in less than 24 hours. Common clinical signs include lethargy, corneal edema (cloudy appearance), scleral injection (bloodshot appearance), a dilated pupil, and an intraocular pressure reading greater than 30mmHg. The goal of emergency management is to immediately decrease the pressure. Several options exist to achieve this. Topical medications are often effective at quickly lowering pressure. Prostaglandin analogues such as latanoprost (Xalatan™) work very quickly in most canines. Several drops 10-15 minutes apart will usually be enough to decrease the pressure into the normal range within an hour. Other topical glaucoma medications exist and are often useful for long term management, but are not as effective in the emergency setting. Another common strategy to lower intraocular pressure is IV mannitol. This is a hyperosmotic medication that works by causing fluid to flow from the vitreous cavity into the bloodstream. It is administered via an IV catheter at a dose of 1-2 grams/kg slowly (over 15-20 minutes). A third option, typically only performed by ophthalmologists, is a direct aqueous centesis. A small needle (30g) is inserted into the anterior chamber to directly shunt fluid out of the eye. Once the pressure has been lowered, a maintenance medication protocol must be started to keep the pressure in the normal range.Penetrating corneal lacerations are another potential emergency. The most important thing is to recognize the problem and minimize manipulation of the eye. Prompt referral to an ophthalmologist is usually indicated. Emergency treatment usually involves suturing of the cornea under general anesthesia. Treatment with broad spectrum topical and oral antibiotics is needed. Ointments should be avoided for topical therapy to minimize the risk of further trauma. Steroids can be used to minimize inflammation after the risk of infection has passed. Complications can include loss of vision, prolonged uveitis, phthisis bulbi (small eye), and glaucoma.
A descemetocele is a deep corneal ulcer that is 99% eroded through the cornea. These corneas are very fragile and can rupture at any time. These are most common in brachycephalic breeds and typically occur as a result of an infected ulcer. These are nearly always a surgical emergency, although medical management can be successful in select cases. A tectonic graft to improve the strength of the cornea is the recommended option. Several types of grafts include a conjunctival pedicle graft (CPG) and a corneal-conjunctival transposition (CCT). A conjunctival graft has the benefit of bringing an immediate blood supply to the wound, but often leaves a prominent scar. The CCT is more technically challenging, but is nice for central lesions as it transposes clear cornea and decreases the permanent scar. Other management options include globe protection with a third eyelid flap or a temporary tarsorrhaphy. These options are risky as they do not treat the actual problem and corneal rupture can still occur. Application of surgical tissue glue into the ulcer has also been successful, but is not commonly performed. With proper treatment, most deep ulcers will heal and retain at least partial vision.
An anterior lens luxation is an emergency when it causes acute glaucoma. The lens is typically suspended in place behind the iris. In terriers and several other breeds, the zonule fibers that suspend the lens can begin to degenerate as a genetic condition until the lens is free to shift within the eye. If the lens moves through the pupil into the anterior chamber, it can become trapped and obstruct the normal flow of aqueous humor. These dogs often present with very acute onset of cloudy eyes and severe ocular pain. On examination, the lens can usually be identified in the anterior chamber, but it can occasionally be difficult to diagnose, especially if the cornea is opaque. Removal of the lens is the recommended option is there is still potential for vision. This procedure is called an intracapsular lens extraction and involves a large incision to remove the lens in one piece. Risks of the surgery include persistent glaucoma, retinal detachment, and chronic uveitis. Cost is also often a factor with this surgery. If vision has already been lost due to glaucoma, enucleation is usually the preferred option due to the decreased cost and complication rate. In cases where the lens is luxated but has not moved into the anterior chamber, more options exist. An aphakic crescent is the classic sign on exam used to verify that the lens has shifted. Topical therapy with medication to constrict the pupil and prevent anterior movement of the lens is common but may not be a permanent solution. Surgery to remove the lens is often still recommended in a posterior luxation, but is typically not performed in an emergency setting.