Preface

The eye is our window to the world and the loss of its function has a most profound effect on our ability to interact with the world around us. Despite this there is a tendency to underestimate the range, complexity and subtlety of the processes that sustain its function. In this volume we present a view that attempts to draw together various aspects of our understanding of the autonomic neural control of the eye and linked aspects of its pathophysiology.

On one level the contributions highlight the role of the autonomic nervous system in sustaining the balance and normal functions of ocular tissues such as the cornea and on another they highlight its role in the specific visual functions centering around the control of accommodation and pupillary diameter. Whilst the regulation of accommodation is inextricably embedded in the processes of vision, it is intriguing that the preganglionic neurons in the Edinger-Westphal nuclei associated with accommodation and the pupillary light reflex also seem to influence choroidal blood flow and possibly intraocular pressure in the cat. Picking up the latter point regarding intraocular pressure as an example, the issue of the control of intraocular pressure is of enormous clinical significance for the major blinding disease glaucoma. The evidence for the role and pharmacology of the autonomic neural influences in the control of aqueous humour formation thus provides crucial insight into this matter.

Clearly there are many levels of interaction between the systems sustaining the function of the eye and its autonomic innervation and our objective has been to provide in each of the areas covered an insight into the relative significance of the different components. In the retinal vessels for example the autonomic nervous system seems to have little influence, with autoregulatory processes providing the main control of retinal vascular tone and blood flow. While the dual control of vessels by perivascular autonomic and sensory-motor nerves at the advential-medial border and by endothelial vasodilator and vasoconstrictor mechanisms from the intimal side is now recognised (see Burnstock and Ralevic, 1994), there are many special features of the eye that require a level of detail beyond the scope of the present volume such as the afore-mentioned control of intraocular pressure, the blood-aqueous barrier and the origin in the CNS of some nerves controlling blood flow in the eye. Indeed, in some cases these features of the eye lack the research necessary to provide an adequate account.

We have also decided not to devote a separate chapter to diseases of the eye concerned with abnormalities in autonomic function, but rather to refer to disease conditions within

Adam M.Sillito

the separate chapters. However for fuller coverage of this topic the Editors recommend the excellent review by Collins and O’Brien (1990). Finally it is our particular hope that this volume on the Nervous Control of the Eye will act as a stimulus to further work in this important field.

Geoffrey Burnstock and Adam Sillito

REFERENCES

Burnstock, G. and Ralevic, V. (1994). New insights into the local regulation of blood flow by perivascular nerves and endothelium. British Journal of Plastic Surgery, 47, 527–543.

Collins, B.K. and O’Brien, D. (1990). Autonomic dysfunction of the eye. Seminars in Veterinary Medicine and Surgery (Small Animal), 5, 24–36.