For the general practitioner, assessment of a corneal ulcer includes a determination of 1) the likelihood that referral will be needed and 2) the urgency with which this should occur. If surgical repair is likely, the case should be sent ASAP. Our office staff is trained to help triage cases like this; the doctors at Veterinary Vision are always available to help and, if you have determined a case is an emergency, it will be seen the same or the next day. Emergency assistance is available 24/7 by calling our regular office phone number.
When we examine these cases, we do a projection of the potential for perforation to determine whether a surgical graft is needed. Ulcers with a depth of greater than 80% are likely to need surgery. However, if the adjacent cornea exhibits malacia or severe infiltrate, there is the potential for graft failure. In these cases, we may elect to delay surgery for 1-2 days of intensive topical and subconjunctival antibiotic therapy to improve the outcome. In all cases, a risk-benefit assessment guides our treatment plan with surgery reserved for those cases where medication alone is unlikely to be successful.
How are these surgically repaired?
There are two types of grafting procedures used to repair deep ulcers. A conjunctival graft uses vascularized, elastic conjunctival tissue to patch the defect. These have the advantage of providing a source of blood vessels and immune factors that aid in the healing of a septic defect. However, these grafts are opaque and we try to avoid their use when the ulcer involves the visual axis. After a conjunctival graft has healed, transection of the pedicle (under topical anesthesia) is possible to minimize the area of opacity.
A corneoconjunctival transposition mobilizes adjacent, transparent corneal tissue to fill a defect. This type of procedure has the greatest potential to retain transparency. However, it requires that the adjacent cornea be healthy enough for grafting. The size of a defect that can be filled in this way is limited. In this example, the grafted cornea will continue to clear, allowing nearly normal vision.
How about medical management?
One of the questions we are asked by veterinarians on the phone is, “Which is the best antibiotic for corneal ulcers?” Well, the reflex answer is, “The best one is the one that works.” This obviously means that you often don’t know at presentation which would be the “best” single antibiotic. For deep, progressive corneal ulcers, we also don’t have the luxury of time required for a culture and sensitivity as you were taught in Vet School. So, selection is more often based on clinical appearance and the use of the broadest possible spectrum. Equally important to antibiotic selection is the frequency with which it is applied. Topical medication applied to the eye is generally washed away by tears within an hour. Thus, frequent medication may involve HOURLY application of topical antibiotics. And, as we tell the clients, bacteria don’t sleep at night so, for the most severe cases, this involves round the clock treatment. For this reason, we may suggest that they consider hospitalizing their pet at an emergency clinic or, during the day, back at your hospital to make this level of treatment possible for someone who needs to work and to sleep. This intensity of treatment is usually only necessary for 5-7 days.
We often use a combination of ofloxacin (0.3%) and compounded cefazolin (50 mg/ml), each applied every 2 hours, alternating so the eye is treated hourly. In addition to topical treatment, we will frequently administer a subconjunctival injection of gentamicin (4 mg) every 2-3 days. Systemic antibiotics are generally of use only in those cases where there is corneal vascularization. Systemic anti-inflammatory and pain medications are used. An Elizabethan collar is essential to prevent even the smallest opportunity to rub at the eye. Even if the owner insists that “Buffy won’t rub.”
Other emergency conditions that will be covered in our July 14 seminar are:
- Glaucoma… before it’s too late.
- Lens luxation… does it always cause glaucoma?
- Corneal laceration
- Acute blindness… causes that are emergencies.