A consonant construction of the hyaloid and retinal vascular systems by the angiogenic process.

There has been much debate as to whether the retinal vasculature forms by angiogenesis or vasculogenesis, thus angiogenesis is now accepted. We suppose that signals necessary for proper localization and development of the hyaloid and retinal vascular systems are already in place prior to the time at which these systems are developed. The remarkable conservation of vascular patterning suggests that specific genetic programs coordinate its formation. Evidence for a genetic program comes particularly from the characterization of gene-targeted mice and mutational analysis in zebrafish, but the exact genetic pathways remain poorly defined. Considering all the things from the aspect of angiogenesis significant differences exist between the mentioned vascular systems only in their lifetime (a) and location (b): (a) The hyaloid vasculature is a complex of transient intraocular vessels, while the retinal vessels are adapted for the whole life. (b) The hyaloid system fills the interior of the optic cup and this way "occupies" three-dimensional space while the distribution of the retinal vessels is relatively planar (two-dimensional) in the retina. We assume that retinal vessels are "built" in the same manner as the hyaloid vasculature and the outcomes at the embryological, histological, cellular and molecular levels confirm it. We show a consonant construction of both systems. The human organism does not have any rational reason to build up one system (i.e. the hyaloid vasculature) by angiogenesis and practically the same system (i.e. the retinal vessels) by another, de novo process, in the eye. It would be a waste of energy and various essential molecules. Thus, it seems that the retinal vascular system is an advanced copy of the hyaloid vessels (Tab. 1, Ref. 143).