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Contact lens wear (CLW) has been shown to cause an elevation in tear fluid (TF) plasmin levels. This study investigated whether the proteolytic activity assayed by a caseinolytic technique was also bound by CLs and whether certain bacterial species contribute to the production of plasmin. CLs worn by patients with corneal disease showed proteolytic activity in five out of nine cases when examined on casein agar. Histological and electron microscopic examination of the lenses revealed bacterial adherence and growth on both surfaces of the CLs. Strains of Staph. epidermidis, Staph. aureus, Pseudomonas aeruginosa and Branhamella catarrhalis, isolated from eyes with external infections, were cultured on a modified milk casein agar and examined for their proteolytic activity. Neither cultures of Branhamella catarrhalis nor Staph. aureus showed proteolytic activity when examined by direct caseinolytic assay. The proteolytic activity shown by Staph. epidermidis or Pseudomonas aeruginosa was not affected by a proteinase inhibitor aprotinin. However, when exogenous plasminogen was added into the casein agar, Staph. aureus was shown to produce caseinolytic activity. This activity was interpreted to be due to plasminogen activator (PA) activity. It was inhibited by aprotinin. Examination of culture fluids of the bacterial species mentioned above did not show caseinolytic activity. Culture fluid of Staph. aureus contained PA activity. The present study confirms the ability of certain bacterial species to adhere to CLs. Moreover, proteases such as plasmin and bacterial enzymes are present in TF during CL wear and may even adhere to the surface of CLs. Hence, bacterial growth probably contributes to the production of proteases on the ocular surface during CL wear.

Plasmin concentration was determined in tear fluid from 76 eyes showing corneal epithelial disorders, such as corneal ulcers and erosions due to trauma or contact lens wear. Nearly 70% of the eyes with corneal disease had plasmin in their tear fluid, whereas plasmin was present in only 20% of the eyes in a control group of 50 eyes. Re-examination of the plasmin positive control eyes revealed conjunctival bacterial growth or mild subclinical viral infection in most cases. We conclude that plasmin is released into the tear fluid in the presence of corneal or conjunctival lesions or infections, suggesting a pathogenic role of plasmin in these disorders. The significance of the occurrence of plasmin in tear fluid during corneal wound healing is discussed.

In the diagnosis of corneal ulcers, bacterial cultures from scrapings, investigations on viral and fungal growth, as well as staining of smears from the lesion often lead to the correct diagnosis. We report four cases of corneal ulcer where all the methods mentioned failed to reveal the causative microorganism. After the patients had received various medical treatments without any clinical improvement, soft therapeutic contact lenses were fitted, worn overnight, and removed the next morning with sterile forceps. The contact lenses were cultured in blood and Mac Leod agars. Growth of various bacteria was then detected. The infection subsided after the antibiotic treatment was changed according to the bacterial resistance. We conclude that, in selected cases, soft contact lenses may be used for microbiological studies.