Angle-closure, pupil dilatation, and pupil block.

PREVious papers (Lowe, 1964a) have remarked that when the pupils of eyes with shallow anterior chambers, narrow angles, and open peripheral iridectomies are dilated with homatropine, a considerable proportion of the eyes with persistently narrow angles develop angle-closure, a consequent fall in outflow facility, and a rise in intra-ocular pressure that may reach the fifties within two hours. When the same eyes have their pupils dilated equally widely with 1 per cent. I-adrenaline base or 10 per cent. phenylephrine eye-drops, none of the angles closes, facility of outflow is likely to be increased, and small falls in intra-ocular pressure may occur (Lowe, 1964b). The angle-closure induced by homatropine in such eyes is caused by peripheral folding of the iris at the time of pupil dilatation, and the last fold of the iris may be in contact with the lateral wall of the angle so firmly that the iris may push forwards as far as Schwalbe's line, completely smothering the trabeculae. Subsequent unpublished experiments have shown that this type of angle-closure is liable to occur with other tropine-style drugs and that the degree of angle-closure is (in general) related to the width of pupil dilatation. Thus it occurs more frequently after 1 per cent. cyclopentolate ("Mydrilate", "Cyclogyl") than after 4 per cent. homatropine, which in turn causes more angle-closure than 4 per cent. eucatropine ("Euphthalmine") or 0 5 per cent. tropicamide ("Mydriacyl"). The tropine-style drugs therefore act in a similar manner (although to varying degree) as pupil dilators. Likewise, they act in a similar manner (and also to a varying degree) in sometimes causing reduction in facility of outflow even in the presence of an open angle., By contrast, the adrenaline-style drugs-I per cent. I-adrenaline base ("Eppy" 1 per cent.) and 10 per cent. phenylephrine ("Neosynephrine" 10 per cent.)-although equal or more efficient pupil dilators than the tropine group, were found not to cause the iris to fold at the extreme periphery, so that no angles closed in the presence of an open peripheral iridectomy.