Showing papers by "Jitka Cejkova published in 1989"

[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].

Abstract: 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.

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

Abstract: The authors compared on the rabbit eye the tolerance of hydrophilic contact lenses with equal parameters (0.2 mm central and peripheral thickness, 7.4 radius, 15 mm diameter) with a different degree of hydration (37% H2O-Hema), (55% and 65% H2O-Hema-Degma) during continuous wear for a period of two weeks (1, 2, 3, 4, 7 and 14 days). Special attention was devoted to changes in the transparency of the cornea. Changes of the transparency due to wearing of contact lenses were due to changes of corneal hydration. The cause of increased corneal hydration were metabolic and later also morphological disorders in the corneal endothelium. The activity of Na+-K+-dependent adenosine triphosphatase and gamma-glutamyl transferase were reduced, followed by a change in the shape and size of endothelial cells. Later the activities of both enzymes were reduced also in the epithelium. Keratocytes had reduced alkaline phosphatase and gamma-glutamyl transferase activities. The staining properties of glycosaminoglycans in the stroma remained, however, unaltered, similarly as the activity of acid glycosidases and other investigated lysosomal enzymes. The onset of increased corneal hydration caused by a disorder of the active water ion transport and of metabolites in the cornea depended on the percentage of water in hydrophilic contact lenses. It was observed latest after application of contact lenses with 65% water.