The basic factor to be considered when selecting a cycloplegic for refraction is the depth to which it will depress accommodative power without deleterious effect. Secondary factors to be considered are the speed with which the maximum depression is reached, the length of time it is maintained and the speed of complete recovery therefrom.
The ideal cycloplegic is apparently nonexistent. One that will totally abolish accommodation has not been reported. One that is easily administered usually results in inconsistent depression of accommodation, a part of which is due to carelessness relative to administration and to unruly patients and not entirely to the drug itself.
Atropine sulfate ( [C17H23NO3]2H2SO4), probably the best cycloplegic available, and scopolamine hydrobromide (C17H21NO4HBr3) are toxic, and considerable care must be exercised in their administration. It is customary to instil atropine
THORNE FH, MURPHEY HS. CYCLOPLEGICS. Arch Ophthalmol. 1939;22(2):274–287. doi:10.1001/archopht.1939.00860080118011