有病目者问曰∶片脑之功，治目何多？予闻而哂之曰∶君知其功，亦知其害乎？病者愕然
曰∶举世之人，由稚及老，虽愚夫愚妇，皆知片脑为治眼之药，眼科无不以此为先，今君独
言害者何也？莫非骇俗乎！曰∶予非穿凿而好哓舌，亦非绝弃而不用，但用之得其当耳。子既
病目，亦曾点否？曰∶点。曰∶子既点，且以此试为子问，有点片脑，初觉凉快，少顷烦热
而闷燥者；有点片脑，而目愈昏；有点而障愈浓病愈笃者，有之乎？病者曰∶皆有之。且人
之目病，无有不点片脑者。子之目既点片脑，今何为而不愈，而乃矜羡其功之多也？客愀然
而起曰∶诚愚之所未闻，敢请教。曰∶片脑利害兼有，功过相半，然利害虽在片脑之性味，
而功过则由医者用之当不当耳。我以此语子，子静听而以理揆之，且目非热不发，非寒不止
此指大意而言也。若夫血见热则行，见寒则凝，寒甚则伤血，热甚则伤精，此理之自然。
今遍考诸家所论片脑，有称为寒，有称为热，有称为常，有称为劫，皆不知眼科心法之故。
夫片脑寒热兼有，阴中之阳，味凉而性热，实眼科之劫药也。味有形也，性无形也，血有形
也，气无形也，今片脑味凉性热，味不能退无形之火，性不能行有形之血，是以血虽得热而
欲行，而寒又为之绊，火虽得寒而欲退，而热又为之助，故寒反伤其血，热反伤其精。古人
有曰∶寒非纯寒，热非纯热，寒热夹攻，反伤精血，而目之为窍至高，火性炎上，最易攻犯
今内火炽，已怫郁极矣。况其脉道幽深，经络高远，而内治之药，未能便达于目，故用外
劫之药，反攻之法，假其性以引夫邪火从窍而出，假其味以润之，舒其涩痛，且香能通窍，
不过暂用其劫，而不可常也。如凝脂赤肿、天行暴风、蟹睛赤虬、风烂涩痛等症，是其所治
之病也，其他俱不可用耳。如若火息，不赤痛涩烂之症，皆宜减去片脑，片脑之功，只能散
赤劫火，润涩定痛，其害则耗散阳光，而昏眇不明，凝结膏汁，而为白障难除，为其热极生
寒，火兼水化也。屡见患凝脂、赤膜、花翳、蟹睛，皆片脑凝结，成大白片而不得去，方见
片脑生寒，火兼水化之害。大抵目病用片脑，如以贼攻贼，其功亦速，贼败则我胜，若不夺
其权而再纵之，则矫肆生祸乱作矣。故凡用片脑劫病，既退之后，再复多用，则膏汁凝，而
目之光华弱矣。必减片脑用之方妙，而内仍须服补养调治之药，庶不损于瞳神耳。
有一位患眼病的人问道：“冰片（Borneol）的功效，治疗眼病为什么这么多？”我听了便嘲笑他说：“您只知道它的功效，也知道它的危害吗？”病人惊讶地说：“天下人，从幼童到老人，即使是愚笨的男子和妇女，都知道冰片是治疗眼睛的药物，眼科没有不把它作为首选的，现在您唯独说它有危害，为什么呢？莫非是为了惊世骇俗吗？”我说：“我并不是牵强附会而喜欢多嘴，也不是绝对抛弃而不使用，只是使用得当罢了。您既然患有眼病，也曾点过冰片吗？”回答说：“点过。”我说：“您既然点过，那就让我借此机会为您分析一下：有的点了冰片，起初觉得凉爽舒适，过了一会儿却感到烦热、胸闷、烦躁；有的点了冰片，视力反而更加昏花；有的点了之后，内障更加浓重，病情更加严重，有这样的情况吗？”病人说：“都有这种情况。而且人的眼病，没有不点冰片的。您的眼睛既然点了冰片，现在为什么没有痊愈，反而夸耀它的功效多呢？”客人脸色变得严肃，起身说道：“这确实是我未曾听过的道理，冒昧请教。”我说：“冰片利害兼具，功过参半。然而，利与害虽然取决于冰片本身的性味，但功与过则取决于医生使用是否得当。我把这话告诉您，请您静心倾听，并用常理来推究它。况且，眼病不是遇到热邪就不会发作，不是遇到寒凉就不会停止——这里指的是大概的意思而言。至于血液，见到热就会运行，见到寒就会凝滞，寒太甚则会损伤血液，热太甚则会损伤精血，这是自然的道理。
如今遍考各家对冰片的论述，有的称它为寒，有的称它为热，有的称它为平性，有的称它为劫药，这都是不了解眼科心法的原因。冰片寒热兼具，属于阴中之阳，味道凉而性质热，确实是眼科中的劫药。味道是有形的，性质是无形的；血液是有形的，气是无形的。如今冰片味凉性热，其凉味不能消退无形的火邪，其热性不能推动有形的血液，因此，血液虽然因为热而想要运行，但凉寒又束缚着它；火邪虽然因为寒而想要退去，但热性又助长着它。所以，寒反而损伤了血液，热反而损伤了精血。古人曾说：‘寒不是纯寒，热不是纯热，寒热相互夹攻，反而损伤精血。’而眼睛作为窍道位置最高，火性炎上，最容易攻犯头部。如今体内火邪炽盛，已经郁结到了极点。何况脉道幽深，经络高远，内服的药物，不能轻易到达眼部，所以使用外用的劫药，采用反攻的方法，借它的性质引导邪火从窍道排出，借它的味道滋润眼部，舒缓涩痛。而且香气能够通窍，不过是暂时使用它的劫夺之力，而不能经常使用。像凝脂翳、赤肿、天行暴盲、蟹睛、赤膜、风烂、涩痛等症状，是它所治疗的疾病，其他情况都不可以使用。如果火邪平息，没有赤痛涩烂等症状，都应该减去冰片的使用。冰片的功效，只能消散红赤、劫除火邪、滋润干燥、定止疼痛；它的危害则是耗散阳气，导致视物昏花不明，凝结膏汁，形成难以去除的白色内障。这是因为热极生寒，火兼水化之故。多次见到患凝脂翳、赤膜、花翳、蟹睛的病人，都是因为冰片凝结，形成大的白色薄片而无法去除，这才看到冰片生寒、火兼水化的危害。大抵眼病使用冰片，如同以贼攻贼，功效也迅速，贼寇败退则我方胜利；如果不剥夺它的权力而再次放纵它，那么它就会矫情放肆，生出祸乱。所以凡是使用冰片劫夺病邪，在病邪退去之后，如果再继续使用过多，就会导致膏汁凝结，眼睛的光华减弱。必须减少冰片的使用才妙，并且内部仍然需要服用补养调治的药物，这样才不会损伤瞳神（瞳孔及晶状体等内部结构）。
A patient with an eye disease asked, "Why does Borneol (Pian Nao) have so many applications in treating eye diseases?" I heard this and smiled, saying, "Do you know its benefits, but also do you know its harms?" The patient was startled and said, "People throughout the world, from children to the elderly, even foolish men and women, all know that Borneol is a medicine for treating eyes. No school of ophthalmology fails to use it as a first choice. Now you alone speak of its harm. Why? Is it merely to shock the vulgar?" I replied, "I am not being pedantic or fond of idle talk, nor am I advocating its absolute abandonment. I simply advocate using it appropriately. Since you suffer from an eye disease, have you used it as eye drops?" He answered, "Yes." I said, "Since you have used it, let me ask you this: Have you experienced cases where, after applying Borneol, one initially feels cool and comfortable, but shortly thereafter experiences irritability, heat, chest tightness, and restlessness? Have you encountered cases where vision becomes more blurred after application? Or cases where opacity worsens and the condition deteriorates?" The patient said, "All such cases exist. Moreover, no eye disease is treated without using Borneol. If your eyes were treated with Borneol, why have they not healed, yet you still boast of its efficacy?" The guest rose with a solemn expression and said, "This is indeed something I have never heard. I dare to ask for instruction."
I said, "Borneol possesses both benefits and harms; its merits and faults are equal. However, while the pros and cons lie in the nature and flavor of Borneol itself, the actual outcome depends on whether the physician uses it appropriately. Listen carefully and reason through this. Generally speaking, eye diseases do not flare up unless provoked by heat, nor do they subside unless addressed by cold—this refers to the general principle. Blood flows when exposed to heat and coagulates when exposed to cold; excessive cold damages blood, while excessive heat damages essence. This is the natural order.
Reviewing various theories on Borneol, some classify it as cold, some as hot, some as neutral, and some as a 'plundering' drug (Jie Yao). All these views fail to grasp the core principles of ophthalmology. Borneol possesses both cold and hot properties; it is Yang within Yin. Its flavor is cool, but its nature is hot. It is truly a plundering drug in ophthalmology. Flavor is tangible; nature is intangible. Blood is tangible; Qi is intangible. Borneol has a cool flavor and a hot nature. Its cool flavor cannot dissipate intangible fire, and its hot nature cannot move tangible blood. Thus, although blood desires to flow due to heat, it is restrained by cold; although fire desires to retreat due to cold, it is aided by heat. Consequently, cold damages blood, and heat damages essence. As the ancients said: 'Cold is not purely cold, and heat is not purely hot. When cold and heat attack together, they damage essence and blood.' The eye is a orifice located at the highest point. Fire nature tends to blaze upward and easily attacks the head. Currently, internal fire is blazing and extremely stifled. Furthermore, since the meridians are deep and distant, internal medicines cannot easily reach the eyes. Therefore, external plundering drugs are used to employ a counter-attack method: borrowing its nature to guide pathogenic fire out through the orifice, and borrowing its flavor to moisten the eye, relieving dryness and pain. Fragrance can also unblock orifices. One should only temporarily use its plundering power, not continuously. Conditions such as corneal ulceration (Ning Zhi), redness and swelling, epidemic acute blindness (Tian Xing Bao Feng), crab-eye deformity (Xie Jing), red filaments, wind-induced erosion, dryness, and pain are indications for its use. Other conditions are not suitable.
If the fire has subsided and there are no symptoms of redness, pain, dryness, or erosion, Borneol should be reduced or omitted. The efficacy of Borneol lies only in dispersing redness, clearing fire, moistening dryness, and alleviating pain. Its harm lies in depleting Yang energy, causing blurred vision, and condensing ocular fluids into white opacities that are difficult to remove. This is due to extreme heat generating cold, and fire transforming with water. I have frequently seen patients with corneal ulcers, red filaments, floral nebulae, or crab-eye deformities where Borneol condensed into large white flakes that could not be removed. Only then did I witness the harm of Borneol generating cold and fire transforming with water.
Generally, using Borneol for eye disease is like using a thief to fight thieves; its effect is rapid. Once the 'thief' is defeated, we win. But if we do not strip its authority and allow it to run rampant again, it will cause chaos. Therefore, whenever Borneol is used to plunder pathogens, after the pathogens recede, continued excessive use will cause ocular fluids to condense and diminish the luster of the eyes. It is essential to reduce the dosage of Borneol for optimal results. Internally, one must still take nourishing and regulating herbs, so as not to damage the pupil spirit (Tong Shen)."