Kim Young Hyun, Nguyen Thien, Lin Meng C, Peng Cheng-Chun, Radke Clayton J
Vision Science Group, University of California, Berkeley, CA, 94720, United States; Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA, 94720, United States; Clinical Research Center, School of Optometry, University of California, Berkeley, CA, 94720, United States.
Chemical and Biomolecular Engineering Department, University of California, Berkeley, CA, 94720, United States.
Prog Retin Eye Res. 2022 Mar;87:101012. doi: 10.1016/j.preteyeres.2021.101012. Epub 2021 Sep 29.
Hyperosmotic tear stimulates human corneal nerve endings, activates ocular immune response, and elicits dry-eye symptoms. A soft contact lens (SCL) covers the cornea preventing it from experiencing direct tear evaporation and the resulting blink-periodic salinity increases. For the cornea to experience hyperosmolarity due to tear evaporation, salt must transport across the SCL to the post-lens tear film (PoLTF) bathing the cornea. Consequently, limited salt transport across a SCL potentially protects the ocular surface from hyperosmotic tear. In addition, despite lens-wear discomfort sharing common sensations to dry eye, no correlation is available between measured tear hyperosmolarity and SCL-wear discomfort. Lack of documentation is likely because clinical measurements of tear osmolarity during lens wear do not interrogate the tear osmolarity of the PoLTF that actually overlays the cornea. Rather, tear osmolarity is clinically measured in the tear meniscus. For the first time, we mathematically quantify tear osmolarity in the PoLTF and show that it differs significantly from the clinically measured tear-meniscus osmolarity. We show further that aqueous-deficient dry eye and evaporative dry eye both exacerbate the hyperosmolarity of the PoLTF. Nevertheless, depending on lens salt-transport properties (i.e., diffusivity, partition coefficient, and thickness), a SCL can indeed protect against corneal hyperosmolarity by reducing PoLTF salinity to below that of the ocular surface during no-lens wear. Importantly, PoLTF osmolarity for dry-eye patients can be reduced to that of normal eyes with no-lens wear provided that the lens exhibits a low lens-salt diffusivity. Infrequent blinking increases PoLTF osmolarity consistent with lens-wear discomfort. Judicious design of SCL material salt-transport properties can ameliorate corneal hyperosmolarity. Our results confirm the importance of PoLTF osmolarity during SCL wear and indicate a possible relation between PoLTF osmolarity and contact-lens discomfort.
高渗性眼泪会刺激人眼角膜神经末梢，激活眼部免疫反应，并引发干眼症状。软性隐形眼镜（SCL）覆盖角膜，防止其直接经历泪液蒸发以及由此导致的眨眼周期盐分增加。为了使角膜因泪液蒸发而出现高渗状态，盐分必须穿过SCL转运至浸润角膜的晶状体后泪膜（PoLTF）。因此，穿过SCL的盐分转运受限可能会保护眼表免受高渗性眼泪的影响。此外，尽管戴镜不适与干眼有一些共同的感觉，但所测得的泪液高渗与SCL佩戴不适之间并无关联。缺乏相关记录可能是因为在戴镜期间对泪液渗透压的临床测量并未涉及实际覆盖角膜的PoLTF的泪液渗透压。相反，泪液渗透压是在泪液弯月面进行临床测量的。我们首次通过数学方法对PoLTF中的泪液渗透压进行了量化，并表明其与临床测量的泪液弯月面渗透压有显著差异。我们进一步表明，水液缺乏型干眼和蒸发型干眼都会加剧PoLTF的高渗状态。然而，根据镜片的盐分转运特性（即扩散系数、分配系数和厚度）来看，SCL确实可以通过在不戴镜时将PoLTF盐度降低至眼表盐度以下来预防角膜高渗。重要的是，如果镜片的盐扩散系数较低，干眼患者的PoLTF渗透压可降低至不戴镜时正常眼睛的水平。眨眼频率降低会增加PoLTF渗透压，这与戴镜不适一致。对SCL材料盐分转运特性进行合理设计可改善角膜高渗状态。我们的结果证实了戴SCL期间PoLTF渗透压的重要性，并表明PoLTF渗透压与隐形眼镜不适之间可能存在关联。
