凡脏腑之精华，皆上注于目，然所以能光烛远近者，阳之用也。济之以令光明不竭
者，阴之力也。阴阳合德而为精明，非气血独能充其力也。盖气血止为阴阳之标，非即
可以称精华也。而阴阳实为气血之本，所以能致精华也。阴亏则热，故病于目也。红赤
暴痛，眼珠刺疼，夜则更甚，然虽极肿极疼。若视物则能见，岂非阴虚则热，而邪火
乘之，益耗其精神，无以为佐助清阳之用，所以赤肿刺疼，虽不能开目，而开则视物仍
见，可见阴病而阳不病，是为有火者也。阳虚则寒，故病于目也。白翳遮睛，珠不甚
痛，或全不痛，但如青盲，仍能开目，而视物则不见，岂非阳虚则寒，而浊阴犯之，遂
失其如天与日之光而不彰乎？乃阳气自病，是为无火者也。热者，补其真阴，六味汤；
寒者，补其真阳，八味汤。如是则阴阳自复，复能合德而为精明之用矣。（张）幼年
时苦病目，及长而知医，寤寐求之，始得其理，既自济获效，复以是法济人，不论老幼
男女，产后痘后。投无不应。《经》所谓∶知其要者，一言而终。诸病真阴真阳之谓
欤！或以为疑，请以浅近易见之理而喻之，犹灯之能明者火也。资其明之用者，脂膏
也。有脂膏而无火，何以能明？有火而无脂膏，则燎然猛烈，力穷乃止，二者，偏废其
一，便难以成光明之象矣。所谓火中求水，其源不竭，水中求火，其明不灭，一属有
形，一属无形，惟其无形，故能生出有形，盖造化之理，皆生于无也。
凡是脏腑的精华，都会向上汇聚到眼睛，然而之所以能看清远近物体，依靠的是阳的作用。用来资助它使光明不枯竭的，是阴的力量。阴阳和谐配合才能形成敏锐的视力（精明），并非仅靠气血就能独自承担这种力量。大概气血只是阴阳的表现形式（标），不能直接称为精华。而阴阳实际上是气血的根本，所以能够产生精华。
如果阴气亏损就会产生内热，因此眼睛会生病。表现为眼睛红赤、突然剧烈疼痛，眼球刺痛，到了夜晚症状更加严重。虽然肿胀和疼痛非常厉害，但如果看东西仍然能看见，这难道不是阴虚生热，邪火趁机侵犯，进一步耗损精神，导致无法辅助清阳发挥作用吗？所以出现红赤肿胀刺痛，虽然难以睁开眼睛，但一旦睁开仍能看见物体。由此可见，这是阴分有病而阳分无病，属于有火的证候。
如果阳气虚弱就会产生内寒，因此眼睛也会生病。表现为白翳遮蔽瞳孔，眼球不怎么痛，或者完全不痛，只是像青盲症一样，虽然能睁开眼睛，但看东西却看不见。这难道不是阳虚生寒，浊阴之气侵犯，从而失去了像天空和太阳那样的光辉而不显现吗？这是阳气自身患病，属于无火的证候。
对于热证，要补益真阴，使用六味地黄汤；对于寒证，要补益真阳，使用八味肾气汤。这样阴阳自然恢复，又能和谐配合发挥敏锐视力的作用了。（作者）冯楚瞻幼年时深受眼疾之苦，长大后懂得医学，日夜寻求医理，终于掌握了其中的道理。既然自己治疗获得了疗效，又用这种方法救治他人，不论老幼男女，也不论是产后还是痘疹之后，投药没有不奏效的。《黄帝内经》所说：“知道关键的人，一句话就能终结（阐明真理）。”说的就是各种疾病中的真阴和真阳吧！有人对此表示怀疑，请用浅显易懂的道理来比喻：就像灯之所以能明亮，是因为有火。资助火发挥照明作用的，是油脂膏脂。只有油脂膏脂而没有火，怎么能明亮呢？只有火而没有油脂膏脂，就会猛烈燃烧，力气耗尽才停止。这两者，偏废其中任何一个，就难以形成光明的景象了。所谓在火中求水，源头就不会枯竭；在水中求火，光明就不会熄灭。一个属于有形之物，一个属于无形之气，正因为无形，所以能生出有形，大概造化的道理，都生于“无”之中。
The essence of all zang-fu organs ascends and gathers in the eyes. However, the ability to see clearly at both near and far distances relies on the function of Yang (Yang Qi). The force that sustains this and prevents the light from exhausting is the power of Yin (Yin Qi). When Yin and Yang harmonize, they form "Jingming" (sharp vision), which cannot be achieved by Qi and Blood alone. Generally, Qi and Blood are merely the manifestations (biao) of Yin and Yang and cannot be directly termed as "essence." In contrast, Yin and Yang are the root of Qi and Blood, thus generating the essence.
If Yin is deficient, heat arises, leading to eye diseases. Symptoms include redness, acute swelling, and severe pain, with stabbing pain in the eyeballs worsening at night. Although the swelling and pain are extreme, if the patient can still see objects when looking, it indicates that Yin deficiency generates internal heat, allowing pathogenic fire to invade and further consume the spirit. This depletion prevents the assistance of clear Yang, resulting in redness, swelling, and stabbing pain. Even though opening the eyes is difficult, once opened, vision remains possible. This demonstrates a disease of Yin without disease of Yang, characterizing a condition with "fire" (excess heat).
If Yang is deficient, cold arises, also leading to eye diseases. Symptoms include white nebulae obscuring the pupil, with little or no pain in the eyeball. The vision resembles "Qingmang" (blindness with normal appearance), where the patient can open their eyes but cannot see objects. This indicates that Yang deficiency generates internal cold, allowing turbid Yin to invade, thereby losing the brilliance akin to the sky and sun. This represents a self-disease of Yang, characterizing a condition without "fire" (deficiency cold).
For heat conditions, tonify True Yin using Liuwei Dihuang Wan (Six-Ingredient Rehmannia Pill); for cold conditions, tonify True Yang using Bawei Dihuang Wan (Eight-Ingredient Rehmannia Pill). Through this approach, Yin and Yang naturally restore themselves and resume their harmonious function of sharp vision.
During his youth, Zhang [Feng Chuzhan] suffered greatly from eye diseases. Upon mastering medicine in adulthood, he sought its principles day and night, eventually understanding the underlying logic. After achieving efficacy in self-treatment, he applied this method to help others. Regardless of age, gender, or whether the condition followed childbirth or smallpox, his prescriptions were invariably effective. As stated in the *Classic* (*Huangdi Neijing*): "He who knows the essentials needs only one word to conclude." This refers to the True Yin and True Yang of various diseases.
Some may harbor doubts; let us use a simple analogy: Just as a lamp shines due to fire, the substance that fuels this brightness is oil/wax. With oil/wax but no fire, how can there be light? With fire but no oil/wax, the flame burns fiercely until exhausted. If either element is neglected, the phenomenon of light cannot be formed. Therefore, seeking water within fire ensures the source does not dry up; seeking fire within water ensures the light does not extinguish. One belongs to the tangible (form), the other to the intangible (Qi/Spirit). Because it is intangible, it can generate the tangible. Indeed, the principle of creation stems from the "non-being" (Wu).