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The *Yuan Bing Shi* (Treatise on the Causes of Disease) states: Dimness of vision, redness and swelling of the eyes, and the presence of nebulae (membranous opacities) are all considered ulcerative lesions caused by Heat. Even "eye blackness" (a colloquial term for sudden visual loss or darkening), is also caused by Heat. In cases where a person who was previously seeing clearly suddenly loses vision, it is due to severe stagnation of Heat Qi. Some claim that dimness of vision is caused by deficiency-cold of the Liver and Kidney; this is an error. They erroneously assert that the Liver manifests in the eyes and the Kidney governs the pupils, thus falsely attributing dimness to deficiency-cold.

However, Kidney Water belongs to Yin of Winter; when deficient, it should manifest as Heat. Liver Wood belongs to Yang of Spring; when deficient, it should manifest as Cold. How can Kidney Yin and Liver Yang both be deficient and manifest as Cold? Some generally state that within the Liver and Kidney there is Excess-Yin and Deficiency-Yang, providing no explanation for dimness of vision. Laypeople erroneously believe that the Qi of the Liver and Kidney is depleted and cannot reach the eyes. Yet they do not know that the Classics state: "When Heat is extreme, one closes the eyes and experiences 'eye blackness'." Is this caused by Cold?

Furthermore, Zhang Zhongjing stated that in Shanghan (Cold Damage) disease, when Heat reaches its extreme, one becomes delirious and blind. The *Zheng Li Lun* (Correct Principles Discourse) explains that this results from extreme Heat causing Fu Yu (stagnation/oppression) in the eyes. If one cannot see with the eyes nor hear with the ears, it is because Heat Qi is stagnant, causing the Xuan Fu (mysterious pores/micro-channels for fluid and Qi exchange) to close tightly. Consequently, Qi, fluids, blood vessels, Ying (Nutritive) and Wei (Defensive) Qi, and Spirit cannot ascend, descend, enter, or exit. Depending on the severity of the stagnation, the severity of the disease varies. Thus, we know that Heat stagnation in the eyes causes blindness. Therefore, those with slight dimness of vision find it difficult to distinguish objects even at close range because the eye's Xuan Fu have become small and closed, similar to viewing objects through fine silk.

Those who see visions like threads or wings moving have some closure of their Xuan Fu. Those whose vision is dim and who see floating black spots do so because extreme Heat disperses into the eyes. When Hyperactive [Heat] causes harm, it is controlled by the subsequent element, leading to the reverse emergence of tears and turbid fluids. Because these phenomena are close to the eye, even minute ones are visible, appearing like black flowers. Regarding dimness and tearing upon exposure to wind, this occurs because extreme Heat is controlled by Water transformation. Hence, the Classics state: "Jue (Reversal) leads to inability to see." In Jue syndrome, Yang Qi aggregates above and Yin Qi aggregates below. Yang aggregating above means Fire shines alone; Yin aggregating below means Foot-Yin is excessive, leading to distension. Since one portion of Water cannot overcome five portions of Fire, the eyes become dim and blind. Thus, tearing continues unabated upon exposure to wind. When Wind attacks the eyes, Yang Qi remains internally guarded within the Jingming region; this is Fire Qi blazing the eyes, hence tearing occurs upon seeing wind.

According to this discourse, extreme Heat, Fu Yu (stagnation), simultaneous reversal of Yin and Yang, and closure of the Xuan Fu are detailed causes of eye diseases, primarily governed by the transformation of Fire-Heat. If caused by spicy/hot diet, emotional disturbances, or excessive influence of Six Evils leading to Qi-Blood stagnation or deficiency/excess, the theories of Dong Yuan (Li Dongyuan), Hezi (Liu Wansu), and Chen Wuyue are already detailed. However, there are also cases caused by Phlegm-Heat, Damp-Heat, or ingestion of metallic/mineral hot drugs. Additionally, after prolonged illness, weakness of Ying and Wei, insufficiency of Liver Qi and Kidney Yin, decline of Yuan Qi and Essence, or conditions like Tuo Ying (Depletion of Camp) present distinct differences between Deficiency-Heat and Excess-Heat, requiring differentiated treatment.