ABSTRACT
The iris and ciliary body comprise the anterior portion of the uvea-the densely vascularized layer of the eye that is located between the outer scleral coat and the inner
In this chapter, the physiological and pharmacological basis for autonomic neuroeffector transmission in the iris and ciliary body is reviewed. The anterior uvea of the eye is richly supplied with peripheral nerve fibres from sympathetic, parasympathetic and sensory sources. Recent studies show that ocular autonomic nerves contain a variety of peptide and non-peptide cotransmitters in addition to the ‘classical’ neurotransmitters noradrenaline and acetylcholine. Although functional receptors for many of these putative transmitters have been identified in ocular tissues, the physiological significance of cotransmission or modulation in the iris and ciliary body is only beginning to come to light. This chapter begins with a detailed description of the peripheral innervation of the iris and ciliary body and the histological distribution of various neurotransmitters to specific target structures. The subsequent section describes the physiology and pharmacology of autonomic neuroeffector transmission in the iris sphincter and dilator muscles and discusses recent evidence for dual, reciprocal autonomic regulation of these muscles. The final section describes the anatomy and transport physiology of the ciliary epithelium and reviews current evidence for autonomic neural influences on aqueous humour formation. The central role of the adenylyl cyclase system in control of aqueous humour secretion is discussed. Due to species variability in the anatomy, innervation and neurotransmitter content of the anterior uvea, emphasis is placed on human data wherever possible.
