Development of the New Zealand White Rabbit Eye: I. Pre- and Postnatal Development of Eye Tunics.

The New Zealand white (NZW) rabbit has been and is right now regularly utilized in ophthalmic surgery evaluation. Inside NZW rabbit eye, the visibility of ocular structures throughout surgical procedure is fantastic. Younger rabbits are used in different ages for the evaluation of ophthalmic surgery. Complete studies of ocular development in the NZW rabbits have not been reported previously. The aim of the present investigation was to describe the major landmarks and the time course of the pre- and post-natal development of the complete eye tunics of the NZW rabbit to give a superb model as well as a fruitful area for further ophthalmological investigations. Serial histological sections of NZW rabbit prenatal (E13-E28) and post-natal (P1-P14) stages were examined, respectively. The eye of the NZW rabbit developed in a similar manner to that of the human and domestic animals eyes; the principal differences were at the time of occurrence of certain developmental events, absence of pigmentation which represent an exploited benefit for ophthalmic surgery, remarkable Bowman's membrane at E25, poor developed ciliary stroma and juvenile retinal layer until P9. In human, the basic morphogenetic processes of the development of eye tunics are completed towards the end of the first half of gestation period. However, the latter represents the beginning stage of the development of eye tunics in the rabbit. Thus, allowing various extensive ophthalmic researches to be performed.

Scleral spur and ciliary muscle in man and monkey.

The development of the human scleral spur and the role of the scleral spur in human and monkey eyes were studied by measuring the height of the scleral spur, the thickness of the uveal meshwork and the thickness of the longitudinal ciliary muscle. In an attempt to study how the tension of the ciliary muscle is transmitted to the inner wall of the Schlemm's canal, interconnections within the trabecular meshwork were also studied. The results indicate that after 40 weeks of gestation there is little or no further change with aging in the height of the scleral spur but there is a change in shape. The scleral spur is much less developed in monkey eyes than in human eyes. The corneoscleral meshwork predominates over the uveal meshwork in most human eyes while in monkey eyes the situation is the opposite. In man the thickness of the meridional part of the ciliary muscle attached to the scleral spur varies greatly in eyes with a well developed scleral spur. Interconnecting trabecular beams composed of elastic-like fiber were observed in the uveal and corneoscleral meshwork, as well as in the juxtacanalicular meshwork, extending to the cells of the inner wall of the Schlemm's canal. These findings and the dense structure of the scleral spur suggest that in monkey eyes, and at least in some human eyes, contraction of the ciliary muscle causes unfolding of the trabecular meshwork, not so much through the movement of the scleral spur as by movement of the interconnecting trabecular beams and fibers. One important role of the scleral spur is probably to keep the corneoscleral meshwork open when the ciliary muscle relaxes, and another is to enable inward-forward movement of the circular part of the ciliary muscle by pulling the posterior tip of the ciliary muscle anteriorly when the ciliary muscle contracts. A rigid scleral spur is an advantage for these two functions.

Normal uveal melanocytes in culture.

Normal uveal melanocytes of rhesus and cynomolgus macaques can be grown in culture for 3-9 months and subcultured a few times. Postnatal and adult choroidal melanocytes are terminally differentiated cells. They are melanin-containing but not actively melanin-synthesizing cells. They do not undergo cell division, nor do they incorporate tritiated thymidine, but otherwise they are metabolically active. Postnatal and young adult iridial melanocytes are metabolically more active than choroidal cells. They require a feeder cell layer for attachment and to be maintained in a healthy condition. An endothelial cell line established from a rhesus fetal choroid-retina proves to be an effective feeder layer for adult iridial cells. Fetal uveal melanocytes divide slowly and usually require some stimulus and a special culture environment supplemented with 12-O-tetradecanolphorbol-13-acetate and cholera toxin. They can grow and differentiate in vitro. Iridial melanocytes grow and change into cells resembling postnatal choroidal melanocytes. Similar changes occur during development in utero. These findings further suggest that, in vivo, iridial melanocytes migrate and mature to become choroidal melanocytes.

Histochemistry of elastic and related fibres in the human eye in health and disease.

Although the presence of mature elastic fibres in the sclera, trabecular meshwork and Bruch's membrane of the human eye has been recognized for many years, it is only latterly that the existence of the elastic-related fibres oxytalan and elaunin has been appreciated. The microfibrillar component of elastic, oxytalan, which is present in several ocular structures in infancy, can either mature to fully-developed elastic tissue or, as in the cornea, disappear in subsequent years. Deposition of elastic fibres, particularly the incomplete forms, can occur in the post-developmental period in a variety of disease states but the stimulus and functional significance in most situations is obscure. The evidence suggests, however, that the capacity to form elastic-related tissue is not confined to any one cell type.

Ontogeny of substance P-containing structures in the ocular tissue of the rat: an immunohistochemical analysis.

The ontogeny of the substance P-like immunoreactivity (SPI) containing system in the ocular tissue of the rat was examined by means of the indirect immunofluorescence method. SPI-containing amacrine cells first appeared at postnatal day 4 and displaced SPI-containing amacrine cells at postnatal day 5. After this time, they developed markedly reaching their maximum content and distribution at postnatal day 14. On the other hand, SPI-containing cells in the trigeminal ganglion were first seen at gestational day 17 and reached their maximum content at birth. SPI-containing fibers in the cornea and uvea were first observed at gestational days 17-19. The SPI-containing fibers in the iris reached their maximum content at birth, while those in the cornea, choroid and ciliary body were fully developed at postnatal day 3. In the adult rats, numerous SPI structures were still seen in the ocular tissue, retina, cornea and uvea. These findings suggest that SPI might play some role in the developing ocular tissue in addition to its neurotransmitter or neuromodulator role in the adult, because SPI structures appear in the retina before establishment of synaptogenesis and in the cornea and uvea during the fetal stage.