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A collagenase that can digest both collagen fibers in the stroma and the native collagen molecule was found in rabbit corneal epithelium, using a tissue culture assay. Calf, chicken and fetal calf serum added to the tissue culture media inhibited the collagenase, while human and rabbit serum were not inhibitory. Edathamil calcium disodium demonstrated a potent inhibitory effect on the enzyme with minimal toxicity to the epithelial cells. The clinical implications of a corneal collagenase are discussed.

The dynamic visco-elastic properties of human, monkey and rabbit lenses have been measured with a dynamic rheometer. The value for the apparent elastic modulus (Young modulus) of the lens was found to be 10 5 –10 6 dyne/cm 2 in humans and 10 4 –10 5 dyne/cm 2 in monkeys and rabbits. The value for the loss tangent was 0·3–0·4 in the human lens and 0·3–0·6 in rabbit and monkey lenses. Elastic moduli and loss tangents of the lenses showed poor dependence on temperature at 15°–55°C and on frequency of oscillation at 0·01–25 c/s. The lenses showed linear viscoelasticity when the amplitude of oscillation was below 0·02 mm, and they showed non-linear visco-elasticity when the amplitude exceeded 0·03 mm.

Under the conditions of this study, systemically or topically applied thimerosal was found to have no teratogenic effect even when given in concentrations approaching the 50% lethal dose of these compounds. A comparison of topical and subcutaneous administration of thimerosal to rabbits shows that a substantial concentration of mercury was present in blood and tissues of the treated animals and their offspring. Thimerosal was found to cross the blood-brain and placenta barriers.

Nonradioactive idoxuridine (IDU,5-iodo-2'-deoxyuridine), while not teratogenic to rats, does produce fetal maliformations in rabbits when administered topically to the eye in doses similar to those used clinically, 0.1% four times a day for 12 days. These maliformations include exophthalmos and clubbing of the forelegs. By contrast, trifluorothymidine (F3TdR), another highly effective antiherpetic agent currently under investigation but not available for general use, was found not to be teratogenic to rabbits, even when given in concentrations tenfold greater than the doses used to produce idoxuridine teratogenicity.

Collagenolytic activity was found in bovine corneal epithelium using a synthetic substrate. Increased levels were found after physical disruption of the epithelial cells. This activity was inhibited by disodium ethylene diamine tetraacetate. The release of a collagenolytic enzyme from traumatized epithelial cells may be of clinical importance in the pathogenesis of corneal stromal ulcerations.

Peptidase activity, operative at neutral pH, was found in bovine cornea and conjunctiva with a synthetic substrate assay. The same peptidase was found previously in commercial bacterial collagenase preparations. Cell fractionation of homogenates revealed the activity to be maximal in the high-speed supernatant of the corneal and conjunctival epithelium, and in the intermediate fraction of the endothelium. There was no peptidase found in the stroma. EDTA, cysteine, calf serum and calf aqueous inhibited this activity. The specificity and advantages of the substrate are discussed, and the clinical implications of a collagenase-like peptidase system within the cornea are noted.