[Comparison of tolerance to hydrophilic contact lenses made of Hema (37% H2O) and Hema-Degma (55%, 65% H2O) in the rabbit eye. II. Changes in corneal transparency due profound degenerative processes].

The authors investigated on the rabbit eye the effect of long-term continuous wearing (14, 21, 28 days) hydrophilic contact lenses (h. c. l.) with varying degrees of hydration (37%, 55%, 65% water). Long-term wearing of the lenses caused disorders in all corneal layers. These changes are identical in all types of contact lenses, only their onset is earlier and the extent is more marked in contact lenses with a low hydration (37% water). Contrary to epithelial changes in the corneal stroma, the changes are qualitatively different depending on the degree of hydration of the contact lens. Prolonged application of contact lenses with 37% water leads to infiltration of the stroma by inflammatory cells which carry the activities of destructive lysosomal enzymes. The latter are gradually released into tissues and local degenerative processes develop which in some instances culminate by ulceration. Other corneas are vascularized. The described changes in stroma were not found in hydrophilic contact lenses with 55% and 65% water. After prolonged application of highly hydrated contact lenses (65% water) the authors, however, observed uptake of liquid from the upper third of the stroma due to the contact lens which dried on the eye and acted on the cornea as a hypertonic solution. In this subepithelial zone the staining of glycosaminoglycans was reduced, similarly as the enzymatic activities in keratocytes which suggests serious degenerative processes, i. e. disorders in the synthesis of components of the ground substance of the corneal stroma.