Eye exposure to the organophosphorus (OP) irreversible
acetylcholinesterase inhibitor sarin results in long-term
miosis and reduction in visual function.
Anticholinergic drugs, such as
atropine or
homatropine, which are used topically in order to counter these effects may produce
mydriasis and partial cycloplegia, which may worsen visual performance. This study was aimed to test the efficacy of short-acting
anticholinergic drugs against
sarin-induced
miosis and
visual impairment, which will minimally insult vision. Long-Evans rats, exposed topically to various
sarin doses from 0 to 10 μg, showed a dose-dependent
miosis, which returned to pre-exposure levels within 24-48 h.
Tropicamide treatment rapidly widened the
miotic effect to a different extent depending on time following treatment and dosage given.
Cyclopentolate, however, showed a delayed response that finally widened the pupils in a dose-dependent manner.
Atropine treatment showed a rapid widening of the pinpoint pupils exceeding baseline level finally causing
mydriasis. Light reflex test showed that the contraction ability of the iris following
atropine treatment was impaired, as opposed to the use of
tropicamide which facilitated the iris contraction, similar to control. Finally,
tropicamide and
atropine treatments ameliorated the
visual impairment, as opposed to
cyclopentolate, which worsened visual performance. Considering that
tropicamide treatment against
sarin exposure did not cause
mydriasis nor did it impair the iris contraction flexibility as a response to light, the use of this
drug should be taken into consideration as a first-choice topical treatment against OP intoxication.