Effects of rigid gas permeable contact lens extended wear on rabbit cornea assessed by LDH activity, MDH activity, and albumin levels in tear fluid

We used noninvasive biochemical techniques to study the effects on rabbit corneas of 7-day extended wear of rigid gas permeable (RGP) contact lenses of varying oxygen transmissibilities. Corneal effects were assessed through measurement of lactate dehydrogenase (LDH) and malate dehydrogenase (MDH) activities and albumin levels in tears. The RGP contact lenses used had Dk/L(total) values ranging from 33 to 64 x 10^-9 (cm/sec)(mL O₂/mL mmHg) and were of uniform 0.15 mm center thickness. Extended wear of high Dk (Dk/L(total) = 34) and super high Dk (Dk/L(total) = 56) lenses caused an increase in tear LDH activity from 1,190 U/L (before lens wear) to over 18,000 U/L during 7 days of continuous wear. These contact lenses also caused gradual increases in tear MDH activity from 431 U/L (before lens wear) to over 750 U/L after 7 days of continuous wear. Extended wear of the ultra high Dk lens (Dk/L(total) = 64), however, caused no significant increase in LDH or MDH activity in tears. Tear albumin levels in all contact lens wearing eyes increased after 1 day of lens wear, then gradually recovered to normal values after 2 days of continuous wear. The changes in albumin levels did not correlate with Dk/L(total) values of lenses worn. We conclude that: 1) tear LDH and MDH activities can provide an objective, noninvasive method for assessing physiological effects of RGP contact lens wear on the cornea over time; 2) changes in tear albumin levels may reflect the initial adaptive mechanical stress of RGP contact lens wear on the conjunctiva; and 3) ultra high Dk RGP contact lenses appear to permit safe extended wear, producing no increase in LDH or MDH activity in tears after 7 continuous days of use.