Purpose

Corneal nerves comprise the densest sensory network in the body. Dysfunction of the corneal cold sensitive neurons (CSN) is implicated in ophthalmic disorders, including Dry Eye Disease, the most common ocular surface disorder. The preservative Benzalkonium chloride (BAK) and the mydriatic agent Phenylephrine hydrochloride (PHE) are considered to be inactive at the level of the CSNs. The purpose of this study is to test the impacts of continuous exposures to BAK or PHE at their clinically used concentrations on corneal nerve structure and function.

Methods

In vivo extracellular electrophysiology of the rat trigeminal ganglion was used to monitor CSN functional response to stimuli mimicking physiological states and stressors of the cornea. Corneal nerve structure was evaluated by immunostaining.

Results

Among the tested stimuli, cold probe receptive field stimulation and hyperosmolar stress were the most sensitive methods of detecting activity changes. CSN activity was attenuated after 30 min exposure to either PHE or BAK. After an hour-long washout period, BAK-treated neurons failed to recover activity while PHE-treated neurons showed signs of functional recovery. Intraepithelial nerve density was reduced and nerve fragmentation was increased in BAK-treated corneas, while PHE exposure left corneal nerves structurally intact.

Conclusions

Our study suggests that prolonged ocular instillations of BAK or PHE alter CSN activity through two different processes — irreversible neuronal damage in the case of BAK vs. reversible attenuation in the case of PHE.

中文翻译：

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苯扎氯铵，一种常见的眼科防腐剂，会损害大鼠角膜冷敏感神经活动

目的

角膜神经构成了体内最密集的感觉网络。角膜冷敏感神经元 (CSN) 的功能障碍与眼科疾病有关，包括最常见的眼表疾病干眼症。防腐剂苯扎氯铵 (BAK) 和散瞳剂盐酸苯肾上腺素 (PHE) 在 CSN 水平上被认为是无活性的。本研究的目的是测试连续暴露于临床使用浓度的 BAK 或 PHE 对角膜神经结构和功能的影响。

方法

大鼠三叉神经节的体内细胞外电生理学用于监测 CSN 对模拟生理状态和角膜应激源的刺激的功能反应。通过免疫染色评估角膜神经结构。

结果

在测试的刺激中，冷探针感受野刺激和高渗压力是检测活动变化最敏感的方法。CSN 活性在暴露于 PHE 或 BAK 30 分钟后减弱。经过一个小时的清除期后，BAK 处理的神经元未能恢复活动，而 PHE 处理的神经元显示出功能恢复的迹象。BAK 处理的角膜上皮内神经密度降低，神经断裂增加，而 PHE 暴露使角膜神经结构完好无损。

结论

我们的研究表明，长时间眼部滴注 BAK 或 PHE 通过两个不同的过程改变 CSN 活性——BAK 情况下的不可逆神经元损伤与 PHE 情况下的可逆衰减。