References 

1.

Abbot, W. D. and Henry, C. M.: Paredrine. Clinical investigation of sympathomimetic drugs. Amer. J. Med. Sc. 193: 661, 1937.  

2.

Ahlquist, R. P.: A study of adreno­trophic receptors. Amer. J. Physiol. 153: 586-600, 1948.  

3.

Barbae, R. P. and Smith, W. O.: A COMPARATIVE study of Mydriatic and Cycloplegic agents, in human subjects without eye disThere are two opposing forces, the tonic pull of radial muscle fibres having a sympathetic innervation tending to dilate the pupil and the circular muscle fibres having parasympathetic inner­vation tending to constrict the pupil. The mechanism of dilatation of the pupil produced by sympathomimetics is controversial. Whether it is achieved by relaxation of the circular constrictor fibres or it is an active contraction of radial dilator muscle fibres. The theory of active relaxation of sphinctef was supported by JOSEPH, [8] YONKMAN [11] and BEAN AND BOHR [4] by observing that adrenergic agents are much more POTENT in relaxing sphincter pupillae than contracting the dilator pupillae. LOWENFELD [9] showed that sympathomimetics such as, epinephrine, PHENYLEPHRINE and ephedrine dilate the pupil by active contraction of dilator pupillae.

There have been numerous attempts to explain the mechanism of action of sympathomimetics, whether it is through alpha or beta receptors. AHLQUIST [2] concluded that human iris tissue contains only alpha receptors and sympathomimetic drugs act through these receptors only. This view has been subsequently supported by BENNETT, REINKE, ALPERT, BAUM AND LEON. [5] So far there is no study to SHOW whether beta receptors exist in the human iris and what is their distribution, and what is the shape of the pupil when it dilates under the effect of sympathomimetics? This study was undertaken to investigate these problems.