Postoperative endophthalmitis is rare, but it can be devastating. To prevent this bacterial infection, we must first understand it. Staphylococcus epidermidis is the most common causative agent, and the lid margins, including the cul-de-sac, are its usual source. Eighty-two percent of infections are introduced when the patient’s own flora enters the eye from the lid margin, conjunctiva or nasal area during surgery. Sometimes the intraocular lens (IOL) or the instruments you use introduce the pathogen.

Let’s consider what to keep in mind and which treatments work best.

Research has identified several risk factors for endophthalmitis.

• A large inoculum
. Some research on monkeys indicates that an inoculum threshold exists. When a monkey is injected with 103 or fewer S. epidermidis, it doesn’t develop an endophthalmitis, but at 104 it does. The immune system can destroy a small number of bacteria and prevent infection, but is overwhelmed by a large number. We need to minimize the bacteria in the cul-de-sac.
• A broken posterior capsule.
When vitreous moves into the anterior chamber, it provides a culture medium for bacteria. The risk of endophthalmitis is 10 to 15 times higher in patients with broken posterior capsules than in other patients. If you break a posterior capsule, you must treat it aggressively with antibiotics.
• Intraocular lenses.
As you know, the haptics of intraocular lenses (IOLs) are made either of prolene or polymethyl methacrylate (PMMA). Bacteria adhere with greater affinity to prolene than to PPMA. So IOLs made with prolene haptics have five times the risk of association with endophthalmitis that IOLs with PPMA haptics do.
• Diabetes
. Diabetes also seems to increase the endophthalmitis risk, possibly because patients who have diabetes are less able to clear the bacteria from their eyes.

Take the following steps to prevent postsurgical endophthalmitis:

• Treat lid disease preoperatively.
Because the threshold inoculum is so important, it’s vital to treat lid disease, such as blepharitis and canaliculitis, and to keep the surgical field sterile. Preoperative antibiotics can help. Ofloxacin (Ocuflox) and povidone-iodine (Betadine), at 5% to 15%, treat lid disease effectively. Tetracycline, used for a couple of weeks preoperatively, also works. Recommend lid scrubs and perhaps an antibiotic steroid ointment at bedtime, too.
Mupirocin (Bactroban), a super bacitracin, is newly approved for treatment of methicillin-resistant Staphy-lococcus aureus. This gel was approved by the FDA 18 months ago for nasal application. It also has off-label uses before surgery. We rub it on the lids of high-risk patients – those at risk of nosocomial infections who might be resistant to most antibiotics.
Because neither mupirocin nor bacitracin penetrate tissue well, they treat only surface pathogens and don’t affect bacteria in other parts of the body. This helps prevent development of drug-resistant pathogens.
• Isolate the lids.
Drape your patient’s lids with an inclusive, wrap-around drape. We use tape.
• Treat skin diseases preoperatively.
Patients with a skin disease, especially rosacea, should be treated with doxycycline 100 mg b.i.d. preoperatively for 2 weeks, then 100 mg once daily. Doxycycline causes fewer gastrointestinal adverse effects than tetracycline, and its dosing is more convenient than tetracycline’s t.i.d.
• Administer perioperative antibiotics
. The benefits of perioperative antibiotic use are anecdotal and unverified. However, if you believe in perioperative antibiotic prophylaxis, you’ll want broad-spectrum coverage, high solubility, sustained presence in the tear film and low toxicity.
We continue an antibiotic postoperatively until the epithelium has healed – about 3 days to a week.

Up front, we recommend using fluoroquinolones for surgical prophylactic therapy. Let’s look at how we’ve arrived at this decision by reviewing more traditional treatments.

• Dexamethasone
. The traditional prophylactic treatment to use for endophthalmitis is 0.1% dexamethasone (TobraDex), which kills gram-negative organisms. Yet 80% to 95% of postsurgical endophthalmitis cases and corneal ulcers are caused by S. epidermidis or another gram-positive organism. Although you want your antibiotic to have some gram-negative coverage, gram-positive efficacy is more important. So, for example, tobramycin is not the best treatment to use after cataract surgery, photorefractive keratectomy (PRK) or laser in-situ keratomileusis (LASIK).
• Vancomycin.
Vancomycin in a balanced salt solution (BSS) is often used, but it has drawbacks. We believe the cornea serves as an ophthalmic barrier. A basic requirement of antibiotic efficacy is that the antibiotic must penetrate the eye. If it lies on the cornea, it will be ineffective.
Vancomycin, however, stays in the anterior chamber for only 2 hours. It also might not stay in the anterior chamber long enough to affect the pathogens throughout their lifecycle, as is necessary. It can be hard to tell how much vancomycin from the bottle actually enters the eye, too. And one recent study shows that vancomycin is associated with an increased risk of cystoid macular edema.
Still, when we do cataract surgery, we’ll often squirt a bolus of vancomycin under the posterior capsule for prophylactic effect.
Trovafloxacin (Trovan) and levofloxacin (Levaquin) are new, third-generation fluoroquinolones with excellent efficacy against staphylococci and streptococci. They will probably replace vancomycin because of their superior solubility and lower toxicity.
• Tobramycin (Tobrex).
We put tobramycin in BBS, but the amount of the drug that actually gets into the eye is problematic because of its poor solubility. Don’t use tobramycin if you break the posterior capsule, because it will sink and pull on the fovea or the optic nerve, which can cause severe damage. Tobramycin also isn’t effective against staphylococci and streptococci, and it can be toxic.

Because penetration is an important issue with antibiotic use, we studied the extent of penetration into the cornea and aqueous of several fluoroquinolone antibiotics (ciprofloxacin [Ciloxan], ofloxacin and norfloxacin [Chibroxin]). Ofloxacin had five times the penetration of ciprofloxacin and six times that of norfloxacin, which has poor penetration and a limited spectrum of activity.

A fluoroquinolone must have good penetration in the anterior chamber, which both ciprofloxacin and ofloxacin do. It’s impossible to show that one fluoroquinolone antibiotic is better than another for antibacterial prophylaxis during cataract surgery, but there are strong pharmacologic and physiologic reasons to use one that enters the anterior chamber.

Fluoroquinolones have better coverage than aminoglycosides. The most effective way to get antibiotics into the eye is by aggressively dosing with a topical fluoroquinolone. The most aggressive dosing gets 1 mcg to 2 mcg into the anterior chamber.

Fluoroquinolones do have some drawbacks. Some studies claim that ciprofloxacin can be toxic to the corneal epithelium in PRK or phototherapeutic keratectomy. We haven’t seen much toxicity when we use fluoroquinolones q.i.d.

Ciprofloxacin also seems to be more susceptible to chelation in patients who are taking antacids. Cations chelate ciprofloxacin more than they do ofloxacin. These cations are present in Alcon’s BSS (+) and AMO’s BSS (Endosol), so remember that your irrigating solutions can inhibit ciprofloxacin.

Fluoroquinolones are great for ocular isolates, because they’re broad-spectrum. Ofloxacin kills 92% of gram-positive bacteria; ciprofloxacin kills 86%. For gram-negative bacteria, the figures are 98% for ofloxacin and 99% for ciprofloxacin.

For corneal ulcers caused by Pseudomonas aeruginosa, ciprofloxacin might be best. But it doesn’t work well against streptococci, whereas ofloxacin does. Ciprofloxacin and ofloxacin are 85% to 90% effective against S. epidermidis. An hour or two is plenty of time for anterior segment concentration to decrease your inoculum.

We’ll always worry about endophthalmitis. But new medications such as the fluoroquinolones make our responsibility lighter. Be open to therapeutic innovations, and you’ll serve your patients well.