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The *Ling Shu* (Spiritual Pivot), chapter "Da Huo Lun" (Treatise on Great Confusion), states: The essence and qi of the five zang organs and six fu organs all ascend to pour into the eyes, thereby forming the essence of the eyes. The gathering place of this essence is the eye socket (Ke, meaning a hollow or窝; it refers to the gathering and condensing of essence to form a cavity). The essence of bone manifests as the pupil (Tongzi); the essence of sinews manifests as the black part of the eye (Heiyan, i.e., iris/cornea area); the essence of blood manifests as the collaterals (Lu, including major and minor red vessels); the essence of qi gathered in the eye socket manifests as the white part of the eye (Baiyan); and the essence of muscle manifests as the constraints and wrapping (Yueshuo, Guoxie, referring to the upper and lower eyelids). The essence of sinew, bone, blood, and qi combines with the meridians to form the visual system (Mu Xi) (various essences merge with blood vessels to connect to the eye), ascending to connect with the brain and exiting posteriorly at the nape of the neck. It further states: The pupil and black part follow Yin, while the white part and red vessels follow Yang. Thus, when Yin and Yang harmonize, the eyes rotate and become bright and clear. Observing this treatise, the theory of Five Wheels (Wu Lun) and Eight Palaces (Ba Kuo) used by later generations for diagnosing eye diseases likely originates from here.

The so-called "Qi Wheel" (Qi Lun) is the rising and condensation of Metal Essence, which corresponds to the scripture's statement that "the essence of qi in the socket manifests as the white part." The white part belongs to the Lung (Fei), which governs Qi, hence it is called the Qi Wheel. In the Five Elements, the Lung belongs to Metal, which is extremely hard, thus the sclera is particularly firm. The "Wind Wheel" (Feng Lun) is the rising and condensation of Wood Essence, corresponding to "the essence of sinews manifests as the black part." The black part belongs to the Liver (Gan), which governs sinews, belongs to Wood in the Five Elements, and corresponds to Wind, hence it is called the Wind Wheel. Since Wind nature is moving, the cornea/iris is indeterminate in position and has a bluish-green color. The "Blood Wheel" (Xue Lun) is the rising and condensation of Fire Essence, corresponding to "the essence of blood manifests as collaterals." The collaterals belong to the Heart (Xin), which governs Blood, hence it is called the Blood Wheel. In the Five Elements, the Heart belongs to Fire, which has two types: Ministerial Fire and Sovereign Fire, hence it is distributed at the two corners of the eyes without a central wheel. The "Flesh Wheel" (Rou Lun) is the rising and condensation of Earth Essence, corresponding to "the essence of muscle manifests as the constraints and wrapping." It belongs to the Spleen (Pi), which governs muscle, hence it is called the Flesh Wheel. In the Five Elements, the Spleen belongs to Earth, which encompasses all things and covers the other four zang organs. Since the four zang organs are wrapped and bound, when open, they move and perform myriad functions; when closed, they are still and silent.

The "Water Wheel" (Shui Lun) is the rising and condensation of Water Essence, corresponding to "the essence of bone manifests as the pupil." The pupil belongs to the Kidney (Shen), which governs bone and belongs to Water in the Five Elements, hence it is called the Water Wheel. Water is the essence of Tian Yi (One Heaven), so it uniquely occupies the center. Internally, there are six large collaterals connecting to the Heart, Lung, Spleen, Liver, Kidney, and Mingmen (Gate of Life); six middle collaterals connecting to the Gallbladder, Stomach, Large Intestine, Small Intestine, Sanjiao (Triple Burner), and Bladder; and externally, numerous tiny fine collaterals of unknown number. (These collaterals are clearly visible when facing light, even in birds and beasts.) All these collaterals penetrate the brain, connect downward to the zang-fu organs, circulate Qi and Blood, and nourish the eyes through their flow. Therefore, in any eye disease, changes in color, shape, and collaterals become visible, allowing one to verify which internal zang or fu organ is diseased. Externally, there are two apertures to vent Qi, containing various fluids internally that exit as tears. Furthermore, there are Shen Gao (Divine Paste), Shen Shui (Divine Water), Shen Guang (Divine Light), Zhen Qi (True Qi), and Zhen Jing (True Essence), all of which are source fluids nourishing the eye.

Shen Gao refers to the paste-like fluid contained within the eye; if ruptured, thick black fluid flows out. It is formed by the accumulation of refined juices seeping from the Gallbladder, nurturing the pupil spirit; if deficient, damage occurs. Shen Shui originates from the Sanjiao, transformed by the primordial True One Qi of congenital origin. It is invisible inside the eye. If damaged by contact, black paste resembling thick phlegm becomes visible. Outside the eye, it is the moistening water. If Water is deficient, there is a risk of Fire excess causing dryness and agitation; if Water is exhausted, there are deformities of the eye wheels; if Water is consumed and dry, there is danger of dim vision. Deficiency is common, abundance is rare.

Shen Guang is the essence of visual perception. It originates from Heart Fire and operates through Gallbladder Fire. Spirit (Shen) is great in humans, not limited to vision. Even walking, grasping, speaking, laughing, listening, and hearing require the governance of Spirit; otherwise, the body is merely a lifeless form. True Blood (Zhen Xue) resides in the Liver, ascending to nourish the eyes. It refers to the blood in the five zang and six fu organs and meridians, not the scattered blood in muscles and skin, hence called "True." True Qi (Zhen Qi) is nourished by meridians; Qi must precede Blood for nourishment, representing the generated primordial Yuan Qi. True Essence (Zhen Jing) is derived from postnatal and prenatal sources, transformed from True Yuan into fluid, rooted in the Kidney, applied to the Gallbladder, and reaching the essence of the pupil. If any of these are damaged, eye disease arises.

Generally, the eye is round and elongated, with several layers of hard shell externally, containing crisp clarity internally, and enclosing Shen Gao. Outside the paste is Shen Shui, and outside the water is Blood. Blood nourishes Water, and Water nourishes Paste. Inside the paste is a small, dark, bright spot, which is the concentrated essence of the Kidney and Gallbladder. Only this spot is empty, bright, pure, and illuminating infinitely, known as the Water Wheel. However, only when these three (Gallbladder bile, Kidney essence, Heart spirit) are present is full spiritual clarity achieved. When the Five Wheels are complete, external correspondence is extensive (Qi, Wind, Blood, Flesh, Water). Together they are seamless; separately, they are orderly. Water is the substance, Fire is the function. Qi is movement, Spirit is maintenance. They subtly combine Yin and Yang, their light resembling sun and moon. Pupil size is smaller in the morning and larger in the afternoon, following heavenly and earthly waxing and waning. Males tend to have stronger left eyes, females right eyes, distinguishing yin-yang endowment. Rigidity/flexibility, longevity/shortness of life, deceit/honesty, wisdom/foolishness can all be verified by the eyes. Truly miraculous and precious.

There are also Eight Palaces (Ba Kuo). This theory uses the Eight Trigrams and eight directions, internally matching zang-fu organs and differentiating meridians, which seems reasonable. The meanings were fully explained in the Five Wheels section above, so no further elaboration is needed here. Only the names of the Eight Palaces are recorded for verification. 1. Chuan Song Kuo (Palace of Transmission), corresponding to Qian Trigram, located northwest, connecting to Large Intestine and belonging to Lung. 2. Jin Ye Kuo (Palace of Fluids), corresponding to Kan Trigram, located north, connecting to Bladder and belonging to Kidney. 3. Hui Yin Kuo (Palace of Meeting Yin), corresponding to Gen Trigram, located northeast, connecting to Upper Jiao and matching Mingmen. 4. Qing Jing Kuo (Palace of Purity), corresponding to Zhen Trigram, located center, connecting to Gallbladder and belonging to Liver. 5. Yang Hua Kuo (Palace of Nourishment and Transformation), corresponding to Xun Trigram, located southeast, connecting to Middle Jiao and matching Liver collateral. 6. Bao Yang Kuo (Palace of Womb Yang), corresponding to Li Trigram, located south, connecting to Small Intestine and belonging to Heart. 7. Shui Gu Kuo (Palace of Water and Grain), corresponding to Kun Trigram, located southwest, connecting to Stomach and belonging to Spleen. 8. Guan Quan Kuo (Palace of Gate Spring), corresponding to Dui Trigram, located west, connecting to Lower Jiao and matching Kidney collateral. Matching six to eight leaves two unmatched. Repeating Liver and Kidney collaterals is because the eye root originates in Kidney and specializes in Liver, making them superior to other zang organs. These describe the generation and pairing of Five Wheels and Eight Palaces.

Knowing this, one understands that internal injuries involve internal movement of zang Qi, affecting the Five Wheels. External invasions do not originate from zang transformation; external pathogens first attack the collaterals, then pass from collaterals to palaces, and from palaces to wheels. Thus, internal injury manifestations show no swelling or pain, or pain is slight. Vision may gradually blur, night blindness (Ji Mang, Que Mu) may occur, photophobia may arise, inability to focus on distant objects, dryness preventing opening, eyelid shrinking, trichiasis (Dao Jie Quan Mao), green nebula/white membrane, yellow sclera/blue cornea, dilated or constricted pupils, tilted eyes, greasy discharge, angular cheilitis/ulceration, tearing, diplopia (seeing one as two), color distortion (red as white), straight as slanted, curved as straight—these gradual symptoms belong to internal injury, involving zang and Yin.

External invasion manifestations appear suddenly like wind and fire, with unbearable itching and pain. Sensation of sand in the eye, external ulcers, frequent oily tears, sudden onset of astigmatism/star nebula, stinging sensation looking at sun, burning sensation near lamps, accompanied by nasal congestion/toothache or fever/headache—these sudden symptoms belong to external invasion, involving fu and Yang. Therefore, diseases of fu organs are easy to cure, while diseases of zang organs are difficult to heal. For zang diseases, examine which zang and cause; for fu diseases, examine which pathogen and collateral, then regulate, disperse, tonify, or drain. Warmth, cooling, ascending, descending depend on the judgment of skilled practitioners. Select formulas.