THERAPEUTIC FORUM
The Right Weapon in the War on Bugs
Christopher J. Quinn, O.D.
We all know that conjunctival infections are common causes of “pink eye.”
What we don’t always know is the disease etiology, and whether the cause is bacterial
or viral. Here’s an update on what we know about how these bugs attack the eye and
the variety of weapons we can use to battle bacterial conjunctival infections.
Although viruses (adenovirus, herpes virus) cause most infections, bacteria can also
infect the conjunctival surface.
Staphylococcus and streptococcus inhabit the ocular surface, but the lysozymes and
antibodies in the tear film, along with the blinking mechanism, keep their population in
check. Infection occurs when the host’s defenses break down—due to immune
deficiencies or tear film abnormalities—or when a more virulent bacterial strain is
introduced into the microbial flora.
Diagnosis
Patients develop conjunctival hyperemia in one eye followed by the fellow eye several days
later. A thick muco-purulent discharge can accompany the bacterial infection, often
resulting in the lids being stuck together upon waking.
The trick is to differentiate a bacterial from a viral infection. Both often show a
similar historical picture: conjunctival hyperemia in one eye followed by involvement of
the fellow eye. They differ, however, in that most viral bugs are accompanied by
conjunctival follicles and associated pre-auricular lymphadenopathy. The discharge of
viral infections tends to be less intense and more like excessive tearing, with some lid
crusting. Allergic conjunctival reactions cause intense conjunctival hyperemia, but these
are commonly bilateral and almost always are accompanied by itching.
Treatment
Although most bacterial conjunctivitis is self-limited, treatment can shorten the disease,
increase patient comfort and prevent the spread of infection.
With today’s topical antibiotics, we can treat most cases empirically, except when
you suspect gonococcal infection. Because this organism can penetrate an intact corneal
epithelium and cause keratitis and endophthalmitis, cultures and prompt systemic and
intensive topical antibiotic treatment are mandatory. Most other infections will respond
well to treatment options.
The goal is to choose an antibiotic with a broad spectrum of activity and low propensity
for allergic or toxic responses. In true bacterial conjunctivitis, the fluoroquinolones
may best eradicate the infection without causing side effects.
Although some would argue against fluoroquinolones, when a true bacterial infection is
present, I advocate the most effective treatment option to help prevent the development of
resistant bacterial strains.
Even though there is some microbial resistance to fluoroquinolones, they are effective
against most of the major ocular pathogens. Alternatively, the aminoglycoside antibiotics
of gentamycin and tobramycin are quite effective. Although they have a higher rate of
sensitivity reactions and microbial resistance, they are still workhorse antibiotics and
are cost-effective alternatives. Drops can be supplemented with ointments at bedtime.
Other less desirable agents are available. Bacitracin, only available in an ointment, is
very effective against most gram-positive organisms, but less so against gram-negatives.
Erythro-mycin can be effective against both gram-positives and some gram-negatives, but
many staph species are resistant to it.
Sulfacetamide has a wide bacterial resistance and a high rate of allergic reactions.
Polysporin ointment, which is a combination of polymyxin-B and bacitracin, offers a broad
spectrum of activity and a low rate of allergic reaction, but its ointment-only form
limits its use in the daytime.
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