大哉目之为体，乃先天之空窍，肇始之元明，经络之精华，荣卫之膏液，故有金珠玉液
之称，幽户神门之号。究其源，实阴阳蕴气之始，二五凝精之际，神哉空窍，列分左右，妙
合先天，大玄既备，神物渐凝，精明其聚，普照无穷。稽诸古论，则曰∶肺之精腾，结而为
气轮；肝之精腾，结而为风轮；心之精腾，结而为血轮；脾之精腾，结而为肉轮；肾之精腾
结而为水轮。气轮者，白睛是也，内应乎肺，肺为华盖，部位至高，主气之升降，少有怫
郁，诸病生焉，血随气行，气若怫郁，金受火克而亡血，血亡则病变不测，金包在水外，水
来克金，故气轮先赤，金又克木，是以其病渐及于风轮也。金色宜白，故白而光泽者顺也。
风轮者，白睛内之青睛是也。内应乎肝，肝在时为春，春生万卉，而肝开窍于目，肝木主风
故曰风轮。此轮清脆，内包膏汁，有涵养瞳神之功，其色宜青，故青莹者顺也。目有黄浊
者，乃湿热之害，惟小儿之色最正及长，食乎浓味，则泻其气，而色亦异矣。血轮者，两目
角大小红 是也。内应于心，心主血，故曰血轮。夫火在目为神光，火衰则有昏瞑之患，火
盛则有焚燥之殃。虽有两心，而无正轮。心君主也，通于大 ，故大 赤者，实火也。命门
为小心，小心者相火也，相火行君之令，通于小 。小 赤者，虚火也。若心君之主拱默，
则相火自然清宁矣。火色宜赤，惟红活为顺也。肉轮者，脾土是也。脾主肉，故曰肉轮。夫
土为五行之主，故四轮皆脾之包含，土性主静其色宜黄，得血为润，故黄泽为顺也。华佗云
目形类丸。瞳神居中而独前，如日月之丽东南，而晦西北也，内有大络者五，乃心肝脾肺
肾，各主一络，中络者六，膀胱大小肠三焦胆包络，各主一络，外有旁枝细络，莫知其数，
皆悬贯于脑，下达脏腑，通乎血气往来以滋于目。故凡病发，则目中有形色，丝络一一显见
而可验，方知何脏何腑之受病。外有二窍，以通其气，内包诸液，液出则为泪，中有神膏、
神水、神光。真血、真气、真精，皆滋目之液也。神膏者，目内包涵之膏液，膏液如破，则
黑稠水出是也。此膏由胆中渗润精汁，升发于上，积而成者，方能涵养瞳神，此膏一衰，则
瞳神有损。神水者，由三焦而发源，先天真一之气所化，在目之内，虽不可见，若被物触损
伤，则见黑膏之外，有似稠痰出者是也。即目上润泽之水，水衰则有火盛燥暴之患，水竭则
有目轮大小之疾，耗涩则有昏眇之危，亏者多，盈者少，是以世无全精之目。神光者，谓目
中自然能视之精华也。夫神光原于命门，通于胆，发于心，皆火之用事，神之在人也大矣。
在足能行，在手能握，在舌能言，在鼻能嗅，在耳能听，在目能见，有莫知其所以然而然者
夫神源舍乎心，故发于心焉。神如游龙，变化不测，人能静之，抱元守一，岂独目之无病
哉！真血者，即肝中升运于目，轻清之血乃滋目经络之血也。此血非比肌肉间混浊易行之血
因其轻清上升于高而难得，故谓之真也。真气者，即目经络中往来生用之气，乃先天真一
发生之元阳也。大宜和畅，少有郁滞，诸病生焉。真精者，乃先后二天元气所化之精汁，先
起于肾，次施于胆，而后及乎瞳神也。凡此数者，一有所损，目病生矣。大概目圆而长，外
有坚壳数重，中则清脆，内包黑稠神膏一函，膏外则白稠神水，水以滋膏，水外则皆血，血
以滋水，膏中一点黑莹，乃是肾胆所聚之精华。惟此一点烛照鉴视，空阔无穷者，是曰瞳神
此水轮也。其妙有三∶胆汁、肾气、心神也。五轮之中四轮不能视物，惟瞳神乃照物者，
风轮则有包卫含养之功，故凡风轮有损，瞳神不久留矣。此即唇亡齿寒，辅车相根据之意也。
或曰∶瞳神水乎？气乎？血乎？膏乎？曰非血，非气、非水、非膏，乃先天之气所生，后天之气
所成，阴阳之妙蕴，水火之精华。血养水，水养膏，膏护瞳神。气为运用，神则维持，喻以
日月，其理相同而午前则小，午后则大，亦随天地阴阳之运用也。大抵目窍于肝，生于肾，
用于心，润于肺，藏于脾，有大有小，有圆有长，皆由人禀受之异也。男子右目不如左目之
精华，女子左目不如右目之光彩，此各得其阴阳之定理也。然贤愚佞直，刚柔寿夭，皆验目而
知之，物之丝发差别可以辨，物之毫忽轻重可以定，遇物即知，远射无遗，岂不为神哉之至
宝乎！故古人曰∶天无二曜，一物无所生，人无两目，一物无所见。诚哉是言也，思之甚可
惊畏。夫人之精血有限，岂可妄自斫丧真元，一旦疾成始悔，究其因皆从耽酒恋色，嗜
欲无穷，或痰火头风，哭泣太伤，思虑过度，风沙烟障，不知避戒，竭视劳瞻，而不知养息
或五味四气，六欲七情，不节之所致也。由微至着，而人不知省，及疾已成矣。仍仗血气
之盛而不医，或泥巫祷灵而不治，遂成痼疾，悔怅无由，虽有金谷之富，台鼎之荣，即卢扁
复生，亦不能疗。吁嗟！堂堂之躯，同于木之偶耳。经云∶欲无其患，先制其微。盖言疾之
初起，即当疗治也。制之之法，岂独药哉！内则清心寡欲，外则惜视缄光，盖心清则火息，
欲寡则水生，惜视则目不劳，缄光则膏常润，脏腑之疾不起，眼目之患即不生，何目疾之有
哉！孔子曰∶目不视邪色。戒颜子曰∶非礼勿视。皆所以正其视，养心神也。而孟夫子亦曰
胸中不正，则眸子 焉。又曰∶物交物，则引之而已矣。岂非目由心之所使，心为目
之所诱乎？故老子又曰∶含眼光，缄真气。还真子曰∶目不着于物，则心无所用，心无所用
则神不驰，神不驰兮心自固。岂非心不正由目之妄视乎？故古之圣贤，保之有方，守之有
道，缄舌含光，清心塞听，以养天真。则存德养身，不但目之无病，而寿亦延纪矣。
眼睛作为人体的至宝，其形体乃是先天形成的空窍，是生命初始的元明之光，也是经络中的精华、营卫之气所化的膏液，因此有“金珠玉液”的美称，被称为“幽户神门”。探究其本源，实则是阴阳蕴育之气的开始，是天地二气与五行精气凝结的时刻。这神奇的空窍，分列左右，精妙地契合先天之理。当大玄（宇宙根本规律）具备之后，神灵之物逐渐凝聚，精明之气汇聚于此，普照无穷。
查阅古代医论，有这样的说法：肺的精气升腾，凝结而成气轮；肝的精气升腾，凝结而成风轮；心的精气升腾，凝结而成血轮；脾的精气升腾，凝结而成肉轮；肾的精气升腾，凝结而成水轮。
气轮，就是白睛（眼白部分）。它内应于肺，肺为华盖（五脏中位置最高的脏器），部位最高，主管气的升降。如果稍有郁结，各种疾病就会产生。血随着气运行，如果气机郁结，金（肺）受火（心）克制而耗损血液，血液亡失则病变难以预测。金包在水（肾）之外，水来克金，所以气轮先变红；金又克木（肝），所以病情逐渐波及到风轮。金色适宜白色，所以白而光泽的是顺证。
风轮，就是白睛内部的青睛（黑眼球部分）。它内应于肝，肝在季节上对应春季，春天万物生长，而肝开窍于目，肝木主风，所以称为风轮。这个轮部清脆，内部包裹着膏汁，具有涵养瞳神的功能，其颜色适宜青色，所以青莹透亮的是顺证。如果眼睛出现黄浊，那是湿热的危害。只有小儿的颜色最纯正，长大后如果食用浓腻厚味的食物，就会耗泄正气，颜色也会改变。
血轮，就是两眼内外眼角的大眦和小眦处的红色部分。它内应于心，心主血，所以称为血轮。火在眼中表现为神光，火衰则有昏蒙黑暗的隐患，火盛则有焚燥的危害。虽然有心，但没有正定的轮部。心为君主之官，通于大眦，所以大眦赤红，是实火。命门为小心，小心即相火，相火执行君火的命令，通于小眦。小眦赤红，是虚火。如果心君保持拱默（清静无为的状态），那么相火自然清宁。火色适宜赤红，只有红润活泼才是顺证。
肉轮，就是脾土。脾主肌肉，所以称为肉轮。土为五行之主，所以其他四轮都包含在脾土的统摄之中。土性主静，其色适宜黄色，得到血的滋润，所以黄而润泽的是顺证。
华佗说：眼睛的形状像丸状。瞳神居中且单独向前突出，如同日月照耀东南方，而晦暗西北方。内有五条大络脉，分别是心、肝、脾、肺、肾，各自主管一条络脉；中间有六条络脉，分别是膀胱、大小肠、三焦、胆、心包络，各自主管一条络脉；外部还有旁枝细络，数量不知多少，这些都悬挂贯通于脑部，向下通达脏腑，通行气血往来以滋养眼睛。所以凡是疾病发作，眼中就会出现形色变化，丝络一一显现可见从而可以验证是哪一脏哪一腑受了病邪。
外部有两个窍道，用来通气，内部包裹各种液体，液体流出就是泪液。其中有神膏、神水、神光。真血、真气、真精，都是滋养眼睛的液体。
神膏，是眼睛内部包裹涵容的膏液。如果膏液破损，就会有黑稠的水流出。这种膏由胆中渗润的精汁，升发于上，积累而成，才能涵养瞳神。这种膏一旦衰退，瞳神就会受损。
神水，由三焦发源，是由先天真一之气所化生。在眼睛内部，虽然看不见，但如果被物体触碰损伤，就会在黑膏之外，看到类似稠痰流出的东西。这就是眼睛上润泽的水。水衰则有火盛燥暴的隐患，水枯竭则有眼睛大小轮部的疾病，消耗干涩则有昏花渺茫的危险。亏损的多，充盈的少，所以世上没有完全精纯完美的眼睛。
神光，是指眼中自然能视物的精华。神光源于命门，通达于胆，发源于心，都是火的作用。神在人身上作用巨大。在脚能行走，在手能握持，在舌能言语，在鼻能嗅闻，在耳能听声，在眼能见物，有一种不知道为什么会这样的奇妙。神的源头寄托在心，所以发源于心。神如游龙，变化莫测，人如果能使其安静，抱元守一，难道只是眼睛没有疾病吗？
真血，就是从肝中升运到眼中的轻清之血，它是滋养眼目经络的血。这种血不同于肌肉间混浊易行的血，因为它轻清上升至高处以难得，所以称为真。
真气，就是眼目经络中往来生用的气，是先天真一发生之元阳。非常宜和畅，稍有郁滞，各种疾病就会产生。
真精，是先后天元气所化生的精汁，先起于肾，其次施于胆，然后及于瞳神。凡此几种，只要有一种受损，眼病就会产生。
大概眼睛圆而长，外部有几层坚硬的壳，中间则清脆，内部包裹着一函黑稠的神膏，膏外则是白稠的神水，水以滋养膏，水外则全是血，血以滋养水，膏中有一点黑莹，乃是肾胆所聚的精华。只有这一点烛照鉴视，空阔无穷的，就叫做瞳神，这就是水轮。它的奥妙有三点：胆汁、肾气、心神。五轮之中，四轮不能视物，只有瞳神能照见物体。风轮有包卫含养的功能，所以凡是风轮有损伤，瞳神就不能久留了。这就是唇亡齿寒、辅车相依的意思。
有人问：瞳神是水吗？是气吗？是血吗？是膏吗？回答说：不是血，不是气，不是水，不是膏，而是先天之气所生，后天之气所成，是阴阳的妙蕴，水火精华。血养水，水养膏，膏保护瞳神。气负责运用，神负责维持。比喻为日月，道理相同，但午前则小，午后则大，也随着天地阴阳的运用而变化。
大致来说，目窍通于肝，生于肾，用于心，润于肺，藏于脾。眼睛有大小的区别，有圆长的不同，这都是由于人禀受的差异造成的。男子的右眼不如左眼的精华，女子的左眼不如右眼的光彩，这是各自符合阴阳的定理。然而贤愚、奸直、刚柔、寿夭，都可以通过观察眼睛来知晓。细微的差别可以辨别，毫忽的轻重可以确定，遇到事物即刻知晓，远射无遗漏，岂不是神妙的至极之宝吗！
所以古人说：天上没有两个太阳，一个物体就无法产生；人没有两只眼睛，一个物体就无法看见。这话确实如此，深思起来令人惊畏。人的精血是有限的，怎么可以妄自砍伐丧失真元，一旦疾病形成才开始后悔，追究原因，都是因为沉溺酒色，嗜欲无穷，或者痰火头风，哭泣太伤，思虑过度，风沙烟障，不知道避开禁忌，竭尽视力劳损瞻望，而不知道休养。或者是五味四气、六欲七情，不加以节制所致。由微小发展到显著，人们却不知道反省，等到疾病已经形成，仍然倚仗血气旺盛而不就医，或者迷信巫术祈祷神灵而不治疗，于是成为顽固疾病，悔恨无奈，即使有金玉财富、高官显荣，即使卢医扁鹊再生，也不能治愈。唉！堂堂身躯，同于木偶罢了。经书说：想要没有祸患，先遏制其萌芽。说的是疾病初起时，就应该治疗。遏制的方法，难道只是药物吗！对内则要清心寡欲，对外则要爱惜视力、收敛目光。心清则火息，欲寡则水生，爱惜视力则眼睛不劳累，收敛目光则膏液常滋润，脏腑的疾病不起，眼目的祸患就不生，哪里会有眼疾呢！
孔子说：目不视邪色。告诫颜回说：非礼勿视。都是为了端正视线，养护心神。孟子也说：胸中不正，则眸子眊焉（眼神昏暗）。又说：物交物，则引之而已矣。难道不是眼睛由心所驱使，心被眼睛所诱惑吗？所以老子又说：含眼光，缄真气。还真子说：目不执着于外物，则心无所用，心无所用则神不驰散，神不驰散则心自然稳固。难道不是心不正由眼睛的妄视引起吗？所以古代的圣贤，保养眼睛有方法，守护眼睛有道术，缄舌含光，清心塞听，以养护天真。这样存德养身，不仅眼睛没有疾病，寿命也能延长。
The eye, as the supreme treasure of the human body, is a hollow cavity formed in the pre-heaven (innate constitution), the primordial brightness at the beginning of life, the essence of the meridians, and the paste-like fluid transformed from Ying (Nutritive) and Wei (Defensive) Qi. Therefore, it is called "Golden Pearl and Jade Fluid" and referred to as the "Dark Chamber and Divine Gate." Investigating its source, it is actually the beginning of Yin and Yang nurturing Qi, the moment when Heaven and Earth's two energies condense with the five elements' essence. This miraculous hollow cavity is arranged left and right, exquisitely conforming to pre-heaven principles. Once the Great Mystery (fundamental laws of the universe) is complete, divine substances gradually condense, and clear spirit gathers here, illuminating infinitely.
Consulting ancient theories: The essence of the Lung ascends and condenses to form the Qi Wheel; the essence of the Liver ascends and condenses to form the Wind Wheel; the essence of the Heart ascends and condenses to form the Blood Wheel; the essence of the Spleen ascends and condenses to form the Flesh Wheel; the essence of the Kidney ascends and condenses to form the Water Wheel.
The Qi Wheel refers to the Bai Jing (White Sclera). It internally corresponds to the Lung. The Lung is the Canopy of the Five Zang Organs, located at the highest position, governing the ascending and descending of Qi. If there is slight stagnation, various diseases arise. Blood follows Qi; if Qi stagnates, Metal (Lung) is overcome by Fire (Heart), leading to blood loss. When blood is lost, pathological changes become unpredictable. Metal is wrapped outside Water (Kidney); Water overcomes Metal, so the Qi Wheel turns red first. Metal also overcomes Wood (Liver), so the pathology gradually extends to the Wind Wheel. The color of Metal should be white; thus, white and lustrous indicates a favorable condition.
The Wind Wheel refers to the Qing Jing (Cornea/Iris area inside the sclera). It internally corresponds to the Liver. In terms of seasons, the Liver corresponds to Spring, when all plants grow. Since the Liver opens into the eyes and Liver-Wood governs Wind, it is called the Wind Wheel. This wheel is crisp and contains paste-like fluid internally, which has the function of nourishing the Pupil Spirit. Its color should be green/cyan; thus, clear and bright cyan indicates a favorable condition. Yellow turbidity in the eyes is caused by Damp-Heat. Only children have the purest color; as they grow up and consume rich flavors, their Qi is drained, and their color changes.
The Blood Wheel refers to the red areas at the inner and outer canthi (angles) of both eyes. It internally corresponds to the Heart, which governs Blood, hence the name Blood Wheel. Fire manifests as Divine Light in the eyes. If Fire is deficient, there is a risk of dimness and darkness; if Fire is excessive, there is the disaster of burning and dryness. Although there are two hearts (referring to anatomical lobes or functional aspects), there is no fixed wheel. The Heart is the Monarch, connecting to the outer canthus; redness in the outer canthus indicates Excess Fire. the Ming Men (Gate of Life) is the "Small Heart," and the Small Heart is Ministerial Fire. Ministerial Fire executes the orders of the Sovereign Fire and connects to the inner canthus. Redness in the inner canthus indicates Deficient Fire. If the Heart Monarch remains tranquil and inactive, Ministerial Fire naturally becomes clear and peaceful. The color of Fire should be red; only vibrant red indicates a favorable condition.
The Flesh Wheel refers to the Spleen-Earth. The Spleen governs flesh/muscles, hence the name Flesh Wheel. Earth is the master of the Five Elements, so the other four wheels are encompassed by the Spleen. Earth's nature is quiet, and its color should be yellow. Nourished by Blood, yellow and moist indicates a favorable condition.
Hua Tuo said: The shape of the eye resembles a sphere. The Pupil Spirit is centered and protrudes forward alone, like the sun and moon shining on the southeast while being dim in the northwest. There are five major collaterals internally, belonging to the Heart, Liver, Spleen, Lung, and Kidney, each governing one collateral. There are six middle collaterals, belonging to the Bladder, Large Intestine, Small Intestine, San Jiao (Triple Burner), Gallbladder, and Pericardium, each governing one collateral. Externally, there are numerous branch collaterals whose number is unknown. All these hang and connect to the brain, extending downward to the Zang-Fu organs, circulating Qi and Blood to nourish the eyes. Therefore, whenever disease occurs, colors and shapes appear in the eyes, and the network vessels become visible for verification, allowing one to know which Zang or Fu organ is diseased.
Externally, there are two orifices to allow Qi passage. Internally, various fluids are contained; when these fluids exit, they become tears. Inside, there are Shen Gao (Divine Paste), Shen Shui (Divine Water), and Shen Guang (Divine Light). True Blood, True Qi, and True Essence are all fluids that nourish the eyes.
Shen Gao is the paste-like fluid contained within the eye. If this paste breaks, dark and thick water flows out. This paste is formed by the accumulation of essence fluid seeping from the Gallbladder and rising upward. It can only nourish the Pupil Spirit after formation. If this paste declines, the Pupil Spirit is damaged.
Shen Shui originates from the San Jiao and is transformed from the Pre-heaven True One Qi. Inside the eye, although invisible, if touched and injured by objects, one can see something resembling thick phlegm appearing outside the black paste. This is the moistening water on the eye. If Water declines, there is a risk of Excess Fire and dryness/agitation; if Water dries up, diseases of the eye wheels occur; if consumed and dry, there is a danger of dim vision. Loss exceeds gain, so there are no perfectly pure eyes in the world.
Shen Guang refers to the essence in the eye that enables natural vision. Shen Guang originates from the Ming Men, connects to the Gallbladder, and emanates from the Heart. It functions through Fire. The role of Spirit in humans is great. It allows walking in the feet, grasping in the hands, speaking with the tongue, smelling with the nose, hearing with the ears, and seeing with the eyes. There is a mystery where one does not know why it happens. The source of Spirit resides in the Heart, so it emanates from the Heart. Spirit is like a roaming dragon, changing unpredictably. If people can calm it, embrace the Origin, and guard the One, will it not benefit not only the eyes but the whole body?
True Blood is the light and clear blood ascending from the Liver to the eyes, which nourishes the eye meridians. This blood differs from the turbid and easily flowing blood in muscles. Because it is light, clear, rises to the high position, and is rare, it is called "True."
True Qi is the Qi circulating and functioning within the eye meridians, which is the Primordial Yang generated from the Pre-heaven True One Qi. It should be harmonious and smooth; slight stagnation leads to various diseases.
True Essence is the essence fluid transformed from the Yuan Qi of Pre-heaven and Post-heaven. It starts in the Kidney, then acts on the Gallbladder, and finally reaches the Pupil Spirit. If any of these are damaged, eye diseases arise.
Generally, the eye is round and long, with several layers of hard shell externally, crisp internally, containing a container of dark-thick Shen Gao. Outside the paste is white-thick Shen Shui; Water nourishes Paste. Outside the water is Blood; Blood nourishes Water. In the center of the paste is a spot of black brilliance, which is the gathered essence of the Kidney and Gallbladder. Only this spot, illuminating and viewing with infinite openness, is called the Pupil Spirit, which is the Water Wheel. Its wonder lies in three aspects: Gallbladder Juice, Kidney Qi, and Heart Spirit. Among the Five Wheels, the four cannot see objects; only the Pupil Spirit can illuminate objects. The Wind Wheel has the function of protection and nourishment; thus, if the Wind Wheel is damaged, the Pupil Spirit cannot remain long. This is the meaning of "if the lips are gone, the teeth will be cold" and "the cheekbone and jaw support each other."
Someone asks: Is the Pupil Spirit Water? Qi? Blood? Paste? The answer is: It is neither Blood, nor Qi, nor Water, nor Paste. It is born from Pre-heaven Qi and formed by Post-heaven Qi, the wonderful accumulation of Yin and Yang, and the essence of Water and Fire. Blood nourishes Water, Water nourishes Paste, and Paste protects the Pupil Spirit. Qi handles operation, and Spirit maintains it. Comparing it to the sun and moon, the principle is the same: smaller in the morning, larger in the afternoon, following the operation of Heaven and Earth's Yin and Yang.
Generally, the eye orifice connects to the Liver, is born from the Kidney, is used by the Heart, is moistened by the Lung, and is stored by the Spleen. Eyes vary in size and shape (round or long) due to individual constitutional differences. In men, the right eye is less essential than the left; in women, the left eye is less brilliant than the right. This conforms to the fixed principles of Yin and Yang. However, wisdom vs. folly, flattery vs. honesty, rigidity vs. flexibility, longevity vs. premature death can all be verified by observing the eyes. One can distinguish minute differences and determine slight weights. Recognizing objects instantly and seeing far without omission—how can this not be the supreme treasure of divinity!
Thus, the ancients said: "Heaven has no two suns; without one, nothing can be born. Humans have no two eyes; without them, nothing can be seen." These words are true and thought-provoking. Human Jing (Essence) and Blood are limited. How can one recklessly destroy the True Yuan? Regretting only after disease forms, tracing the cause reveals indulgence in alcohol and lust, endless desires, Phlegm-Fire headache, excessive crying, overthinking, exposure to wind/sand/smoke without avoidance, visual fatigue without rest, or lack of moderation in the Five Flavors, Four Qi, Six Desires, and Seven Emotions. From subtle to manifest, people fail to reflect. By the time disease forms, relying on robust Qi without medical treatment, or trusting witchcraft and prayers instead of curing, leads to chronic illness. With regret and no recourse, even with immense wealth and high status, if Lu Qian (famous physicians) were reborn, they could not cure it. Alas! The noble body is like a wooden puppet. The Classic says: "To avoid disaster, control it at its inception." This means treating disease when it first arises. The method of control is not just herbs! Internally, one must clear the mind and reduce desires; externally, one must cherish vision and conceal light. Clear mind extinguishes Fire; reduced desires generate Water; cherishing vision prevents eye strain; concealing light keeps paste moist. If Zang-Fu diseases do not arise, eye problems do not occur. How could there be eye diseases?
Confucius said: "Do not look at evil colors." He warned Yan Hui: "Look not contrary to propriety." Both aim to correct vision and nourish Heart Spirit. Mencius also said: "If the chest is not upright, the pupils will be dim." And: "When things interact with things, they lead us away." Is it not that the eyes are directed by the Heart, and the Heart is seduced by the eyes? Thus, Laozi said: "Contain the gaze, seal the True Qi." Zhenhuanzi said: "If the eyes do not cling to objects, the Heart has no use; if the Heart has no use, Spirit does not scatter; if Spirit does not scatter, the Heart naturally stabilizes." Is it not that an unrighteous Heart stems from the eyes' wrongful gazing? Therefore, ancient sages preserved eyes with methods and guarded them with Dao: sealing the tongue, containing light, clearing the mind, blocking hearing, to nourish True Nature. By preserving virtue and nourishing the body, not only will the eyes be free of disease, but lifespan will also be extended.