CORNEAL ACIDOSIS DURING CONTACT-LENS WEAR - EFFECTS OF HYPOXIA AND CO2

  • 1 September 1987
    • journal article
    • research article
    • Vol. 28  (9) , 1514-1520
Abstract
The effects of tear-film hypoxia and contact lens wear on human in vivo stromal pH was tested using a non-invasive fluorometric technique. Hypoxia was produced by exposing the normal open eye to 100% nitrogen gas passed through tight-fitting goggles. Stromal pH dropped from 7.53 .+-. 0.02 to 7.34 .+-. 0.03 (n=12, .+-.SD) within 90 min of nitrogen gas exposure, t1/2 = 20 min. After removing the goggles, stromal pH returned to baseline in 35 min, t1/2=10 min. Wearing a thick hydrogel contact lens which caused a tear PO2.ltoreq.2 mm Hg with the eyes open, reduced stromal pH from 7.55 .+-. 0.02 to 7.15 .+-. 0.04 (n=12, .+-.SD) in 80 min, t1/2=9.5 min. After removing the lens, baseline pH was reached in 40 min, t1/2=4.5 min. The stromal pH differences between hypoxia (N2 only) and contact lens wear were not due to differences in tear temperature between the two procedures (contact lens wear 32 .+-. 1.5.degree. C, goggles 33 .+-. 1.0.degree. C). However exposing to eye to 95% nitrogen-5% carbon dioxide reduced stromal pH to 7.16 .+-. 0.05 (n=7, .+-.SD) in 80 min, t1/2=8 min, which was similar to that produced during contact lens wear. These experiments show that contact lens wear causes corneal acidosis by: (1) the production of protons from hypoxic metabolism; and (2) the acumulation of carbon dioxide behind the lens due to low lens CO2 transmissibility.