Bonanno J A, Polse K A
Invest Ophthalmol Vis Sci. 1987 Sep;28(9):1514-20.
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 less than or equal to 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 degrees C, goggles 33 +/- 1.0 degrees C). However exposing the 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 accumulation of carbon dioxide behind the lens due to low lens CO2 transmissibility.
采用非侵入性荧光测定技术，测试了泪膜缺氧和佩戴隐形眼镜对人体活体基质pH值的影响。通过将正常睁开的眼睛暴露于通过紧贴护目镜的100%氮气中来制造缺氧环境。在暴露于氮气90分钟内，基质pH值从7.53±0.02降至7.34±0.03（n = 12，±标准差），半衰期为20分钟。取下护目镜后，基质pH值在35分钟内恢复到基线水平，半衰期为10分钟。佩戴厚水凝胶隐形眼镜（睁眼时导致泪液PO2小于或等于2 mmHg），80分钟内基质pH值从7.55±0.02降至7.15±0.04（n = 12，±标准差），半衰期为9.5分钟。取下镜片后，40分钟内达到基线pH值，半衰期为4.5分钟。缺氧（仅氮气）和佩戴隐形眼镜之间的基质pH值差异并非由于两种操作之间泪液温度的差异（佩戴隐形眼镜时为32±1.5℃，戴护目镜时为33±1.0℃）。然而，将眼睛暴露于95%氮气-5%二氧化碳中，80分钟内基质pH值降至7.16±0.05（n = 7，±标准差），半衰期为8分钟，这与佩戴隐形眼镜时产生的情况相似。这些实验表明，佩戴隐形眼镜导致角膜酸中毒的原因是：（1）缺氧代谢产生质子，以及（2）由于镜片二氧化碳透过率低，镜片后二氧化碳积聚。
