THE THEOLOGICAL BEHAVIOR OF ANIMAL VITREUS AND ITS COMPARISON WITH VITREAL SUBSTITUTES

Some important eye pathologies, such as diabetic proliferative retinop athy and retinal detachment, are strictly connected to different gel v itreus alterations. Therefore there is a strong need in ophthalmology for vitreal substitutes. Until now many synthetic and natural polymers have been tested as vitreal substitutes, but no one has proved to be an ideal vitreal substitute. An ideal vitreal substitute, apart from o ther characteristics, such as transparency, permanency, biocompatibili ty, etc. must have a theological behaviour compatible with the surroun ding tissues. The viscoelastic behaviour of different animals' gel vit reus, evaluated by means of steady shear viscosity and small-amplitude oscillatory measurements, is typical of solid-like rubbery gels with dynamic elastic modulus G' higher than the dynamic viscous modulus G'' in the typical frequency range investigated (0.05-10 Hz). On the othe r hand the theological behaviour of current or candidate vitreal subst itutes (silicone oil, HPMC, high molecular weight hyaluronic acid and chemically-crosslinked hyaluronic acid), analysed with the same techni que, is generally different from that of natural vitreus.