Development of the rabbit retina. IV. Tissue tensility and elasticity in dependence on topographic specializations

A method is introduced for the quantification of specific compliance and the elasticity of small pieces of living retinal tissue. These pieces are fixed at their margins by means of tissue glue, and loaded with a small iron spherule the bending force of which can be gradually enhanced by the action of an electromagnet. Retinal bending caused by such calibrated forces is measured by a horizontal light microscope, and used for estimations of specific compliance and elasticity of the tissue. Three different particular regions of the rabbit retina--periphery, visual streak, and (prospective) medullary rays--were tested at several post-natal developmental stages. From very early stages on (day 2 p.p.) up to adulthood the peripheral retina was found to be significantly more tensile than the two other central regions. This can be shown to depend greatly on the thickness of the tissue which is lower in the retinal periphery. During early post-natal development, all retinal regions except the (prospective) medullary rays become thinner. The tensility of the tissue increases, with the exception of the medullary rays which reduce their compliance strongly. In the adult retina, however, the tensility of all retinal regions is reduced as compared with the neonatal tissue. This seems to be caused by a constant gradual increase of the elasticity of the retina during development which, in turn, may be caused by several developmental parameters, e.g. the formation of synapses, the outgrowth of glial side branches ensheathing neighbouring neuronal cells, or a reduction in extracellular clefts. It is proposed that these differences in tensility between different retinal regions, may be the cause for differential retinal expansion driven by the intraocular pressure. Thus, simple mechanical features of the tissue may contribute to the formation of important topographic specializations of the retina, e.g. the visual streak as the site of highest visual acuity.