Dear Nikola,

In the diagnosis and treatment of conjunctivitis,
ignorance reigns and theory runs wild. 
(Purulent) conjunctivitis with a discharge of creamy white pus 
is presumptively bacterial in origin.
(Non-purulent) conjunctivitis with a watery discharge, or none at all,
(redness only) is presumptively allergic or viral.
To what extent, if any, non-purulent conjunctivitis "weakens" the tissues
and makes them susceptible to "secondary" purulent conjunctivitis is
speculative, as is the issue whether antibiotics should be prescribed
for presumptively viral conjunctivitis "preventively" to forestall
bacterial overgrowth.

Cultures are problematic, because the healthy conjunctiva is not necessarily
sterile. Results take days to be reported. If the infection is threatening
one does not wish to delay treatment where highly effective antibiotics
are available; otherwise the infection has often resolved by the time 
"the culture comes back." 

Antibiotics to treat conjunctivitis (and keratitis - the much more serious
infection of the cornea) should be applied topically, as drops or ointment.
Not by mouth and not by subcutaneous (under the skin) subconjunctival
(into the conjunctiva), intravenous (into the vein) injection. Nor should
they be given my mouth. Topical antibiotics may be administered as drops
or ointment, instilled by pulling down and placing inside the lower lid.
Drops do not blur the vision, but are washed away by the tears more quickly.
Ointment transiently blurs vision, but maintains a higher antibiotic
concentration with less frequent application.

Because the medication (ointment or drops) is virtually in contact with
the offending bacteria, very high conjunctival concentrations of antibiotic 
are easily obtained, the antibiotics are often highly effective, and
in my experience bacterial resistance has not been a problem. 
The pharmaceutical industry has succeeded in making effective,
inexpensive medications (erythromycin, bacitracin-polysporin) seem obsolete,
and has flooded the market with very expensive and presumably superior
products, eagerly adopted by physicians in the vanguard of scientific
progress, and eagerly paid for by patients,"because my eyes are very
important to me."  I myself have been stubbornly old-fashioned and 
prescribed the same antibiotic, erythromycin eye ointment, for 50 years,
without encountering allergic reactions or "bacterial resistance."
Bacitracin-Polysporin ointment has theoretically a wider spectrum.
(Beware of Neosporin, which is commonly prescribed and is highly allergenic.)

A rare but important potential complication of infectious conjunctivitis
is infectious keratitis, much more likely to occur if the cornea is scratched.
Keratitis can lead to corneal scarring, severe impairment of vision,
and in case of perforation to loss of the eye. The use of topical
antibiotics for conjunctivitis not otherwise requiring treatment to 
decrease the risk of corneal infection is an issue of much theoretical
interest to me. The physician who withholds antibiotics for the 
individual patient in order avoid fostering socially undesirable 
antibiotic resistance, is like the general who sends his soldier to
die on the front lines in order that the battle may be won. When I
went to medical school I did not intend to join the Public Health Army,
but to learn to care for this one individual patient whose life is
peculiarly his own. Perhaps I have, or should have, a flood of 
erythromycin resistant staphylococci on my conscience, - that's 
speculative -, but of hundreds of patients I possibly (over)treated
with erythromycin eye ointment, I had not a single complication, and
none developed a corneal ulcer or endophthalmitis, none went blind.

Jochen