Effect of in vivo and in vitro surface protein deposits on the oxygen permeability of polyhydroxyethylmethacrylate gel contact lenses.

The effect of surface protein deposits on the oxygen permeability of polyhydroxyethylmethacrylate ( polyHEMA ) gel contact lenses was studied using: (1) previously worn lenses with protein deposits accumulated in vivo, and (2) new lenses with protein deposited in vitro. The oxygen permeability (Dk) of the protein-deposited in vivo lenses was determined before and after cleaning, and that of the new lenses before and after in vitro protein deposition. For both groups of lenses, the oxygen permeability did not change significantly after either cleaning (in vivo lenses) or protein deposition (in vitro lenses). It is concluded that surface protein deposits on polyHEMA lenses do not alter the oxygen permeability of the lenses.

Calcium and protein in tears: diurnal variation.

With the use of an automatic titrator for calcium and a microcolorimetric assay for protein, diurnal variations in tear calcium and total protein values were studied in nine subjects during a ten-day period. Tear calcium and total protein concentrations were found to be individualized functions that were dependent on the sampling time and sampling day. Prolonged eye closure resulted in an approximate twofold increase in both tear calcium and total protein concentrations. The concentrations of both species remained relatively constant during the day between 8 AM and 5 PM, exhibiting few substantive variations. Diurnal changes in tear calcium and protein values closely paralleled one another. It was found that the tear concentrations of these two species could be related with a simple linear function, which suggests that calcium binding and transport by tear protein may be occurring.

Calcium in tears and contact lens wear.

Tear calcium levels were measured in 27 normal subjects. An instrumental technique that required only 5- to 10-microL tear samples was used for this purpose. A mean of 2.11 +/- 49 (SD) mg/dl of calcium with a range of 1.05 to 3.49 mg/dl was determined for 67 tear samples from 27 subjects. This is in excellent agreement with more elaborate and previous methods. Various factors involved in tear calcium levels were also studied. Tear calcium levels were not significantly affected by the normal walking-hour wear of either hard or soft contact lenses among 22 women aged 19 to 35 years. Tear calcium day-to-day and diurnal variations were found for five of five subjects in a three-day study. Further studies of these variable phenomena are indicated.