INTRODUCTION

Because of the laminar structure of the eye, flat preparations afford an unusually favourable opportunity to study such structures as retinal and choroidal vessels. Valuable information on the retinal vessels was obtained with flat preparations (Friedenwald 1949, Ashton 1949), with trypsin digestion technique (Kuwabara & Cogan 1960), and with the injection-digest method (Knight 1966). Fluorescein angiographic findings for the iris in different eye diseases (A. Vannas 1969, S. Vannas et al. 1969, Raitta & S. Vannas 1969, Karjalainen 1971) stimulated increasing interest in the iris vasculature at the Helsinki University Eye Hospital. Because of this, study of the blood vessels of the iris with 3at preparations was started in 1969. Being of nearly the same size as the human eye, the pig eye was chosen for subject of study and could be used as a model for the human eye. This type of material was readily available and the pig iris, with its strongly developed vascular wall structures, was also assumed to be especially informative. I t was important to verify the myelinated nerves seen in flat preparations (1) so as to differentiate them without any doubt from the iris vessels. Thus an examination of the course and structure of these nerves was made and included in this study. The results obtained in flat preparations for blood vessels and myelinated nerves were confirmed with light microscopical serial sections and electron microscopically.