Zur Morphologie des Corpus ciliare und seiner Anhangsgebilde im Licht- und Rasterelektronenmikroskop bei verschiedenen Vogelarten

Georg, Christine Elisabeth Structure of the ciliary body and its
annexes in different bird species: a light- and scanning electron
microscopic study. The aim of this study was to clarify the
structure of the ciliary body and its annexes in different bird
species. Therefore the ciliary body, the chamber angle, the fibrae
zonulares and the iris of 52 birds of 19 different species were
examined systemically for the first time, not only by light
microscopy, but also by scanning electron microscopy. Vicarious for
the different types of bulbi oculi were examined gallinaceous
birds, day-active and night-active predatory birds. The examination
showed that the general anatomy of the ciliary body is equal in all
birds. It can be divided morphologically into two parts from
posterior to anterior: the posterior part of the pars plicata and
the anterior part of the pars plicata. A prelenticular pars
plicata, pars plana and transitional region of the iris, as it
exists in mammals for the production of the aqueous humour, cannot
be found in birds. In the avian eye, the aqueous humour is produced
by the anterior part of the pars plicata. Large species-specific
differences in the content of elastic fibres in the ciliary body
could be found. Gallinaceous birds, day-active predatory birds and
the cormorant use lenticular accommodation. Their ciliary body
therefore contains many elastic fibres, while in night-active
predatory birds, which almost exclusively use corneal
accommodation, the ciliary body contains almost none. The size of
the different portions of the ciliary muscle depend on the kind of
accommodation used in the various bird species. In gallinaceous
birds and day-active predatory birds, both main parts of the
ciliary muscle, the ciliaris anterior and posterior muscle are
equal in size. In contrast to this, the anterior portion in
night-active predatory birds and the posterior portion in the
cormorant is much larger. The avian-specific active accommodation
requires an extremely deep cilioscleral sinus in all bird species.
The width of the chamber angle depends on the bulbus type. In
gallinaceous birds it is narrow, while in night-active predatory
birds it is wide open. In day-active predatory birds its width is
intermediate. The pectinate ligament in the bird is not strong
enough to support the structure of the ciliary body. It consists of
thin, mostly parallel cords which pull the ciliary body back into a
relaxed postion when the ciliaris posterior muscle relaxes. In
contrast to this, in the cormorant eye, the pectinate ligament
consists of a very dense network of thick fibres. The examination
of the Schlemm's canal showed clearly, that birds have a sinus
venosus sclerae, in contrast to the plexus venosus sclerae in most
mammals. In the anterior part of the iris of the examined Phasianus
colchicus, Tinnunculus tinnunculus, Hierofalco rusticolus and
Haliaeetus leucocephalus epitheloid cells were found, which are
similar to the pigment cells, typical to many night active
predatory birds.