G1-0-8 Surface anesthesia on the cornea of rabbits

G.1.0.8
Surface anesthesia on the cornea of rabbits
PURPOSE AND RATIONALE
Following the pioneering work of Sollmann (1918),
block of the rabbit corneal reflex as described by
Régnier (1923) has become a standard test method for
evaluating local anesthetics.
PROCEDURE
Albino rabbits of either sex weighing 2.5–3 kg are
placed into rabbit holding cages. The upper and lower
eyelashes are carefully clipped. The conjunctival sac
of one eye is held open, thus forming a pocket. From
a 1 ml syringe with a 22-gauge needle, 0.5 ml of a
solution of the anesthetic is applied into the conjunctival sac for 30 sec. Then the procedure is repeated, so
that 1.0 ml is applied within 1 min. One ml of the
standard (0.1% solution of tetracaine hydrochloride)
is applied to the other eye. Effective local anesthetics
extinguish the corneal reflex (blinking) elicited by
any touch of the cornea. For quantitative purposes,
the irritation with a bristle according to von Frey
(1894, 1896, 1922) has been recommended. An
equine hair bending at a load of 230 mg is attached
perpendicularly to a glass rod. Within 25 sec, the cornea is touched 100 times. The summation of many
stimuli applied this way gives better results than a
single touch with a glass rod. The test is started 5 min
after application of the drug and repeated every 5 min
until anesthesia vanishes and blinking occurs again.
The time between disappearance and reappearance of
the corneal reflex is registered.
EVALUATION
Using the time of loss of the corneal reflex as parameter after application of different doses, dose-response
curves can be established and potency ratios versus
the standard calculated.
MODIFICATIONS OF THE METHOD
Chance and Lobstein (1944) used guinea pigs for
testing surface anesthesia by the corneal reflex.
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