Effects of hyaluronic acid fractions in the rabbit eye. Two fractions of hyaluronic acid with different molecular weight (Ial, molecular weight 500,000-730,000 and Healon, molecular weight 750,000) were injected intracamerally or intravitreously in the rabbit eye. Although the fraction with higher molecular weight caused an increase in intraocular pressure, no change of this parameter was found after administration of the fraction with the lower molecular weight. Furthermore, various inflammatory reactions in ocular tissues were observed during slit-lamp biomicroscopy after administration of Healon but not of Ial. No inflammatory reaction was found after subchronic instillation of the compounds. 