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In ophthalmology, external treatment is called "dian" (topical application), and internal treatment is called "fu" (oral administration). Some cases involve only topical application without oral medication, some involve only oral medication without topical application, and some involve both. Why is this? It is because diseases are categorized as internal or external, and treatments vary in severity. If an internal pathology has formed but there are no external manifestations, topical application is unnecessary; the primary focus should be on oral medication. In the early stages of mild conditions, where there is merely slight pathogenic factor, or after the pathogen has receded leaving residual pathogens, topical application can certainly eliminate them, but combined with oral medication for a pincer attack, it is also effective. If the internal disease is severe and the external symptoms are critical, both root cause and branch symptoms must be addressed rationally, hence both methods are employed simultaneously.

Medicines are used to correct deviations and remedy deficiencies; unless absolutely necessary, either method may be omitted. Modern practitioners often prefer topical applications and disdain oral medications, or use only topical applications to avoid criticism; all these reflect biased judgment. In summary, when the root (ben) is heavier than the branch (biao), topical application should be light. As the saying goes: To stop the flow of water, nothing is better than dredging its source; to cut branches, nothing is better than severing the roots. Stirring soup to stop boiling is inferior to removing firewood from under the pot. When the branch is heavier than the root, oral medication should be light. As the saying goes: Dirty objects must be washed, mirror stains must be polished. Sweat and salt brine cause rust on swords and knives; without polishing, how can they be useful? Clinging to one's superficial views leads to confusion between root and branch; if root and branch are confused, recovery is impossible. The proverb states: When cutting branches, examine the root; while attending to the root, do not forget the branch. Focusing on the interior while neglecting the exterior is called foolishness; treating the interior while losing sight of the exterior is called stupidity. Managing both interior and exterior makes one a good physician.

Preparing medicines is like adjudicating legal cases, navigating between cold and heat, determining life and death. Using medicines is like commanding troops, distinguishing between raw and cooked states, deciding success or failure. A difference of a fraction can lead to results as different as clouds and mud; can one not be cautious? Current mediocre physicians, upon seeing eye diseases, immediately treat them as Fire syndromes. When questioned, they absurdly cite the theory that "without heat, it does not erupt; without cold, it does not stop." They fail to realize that ophthalmology includes many cases of Yin exhaustion and Yang decline, false cold and false heat, which require sweet-warm nourishing formulas. How can one solely claim it is Fire and universally apply cold-cold agents? Cold medicines damage the Stomach Qi and Blood; fear that the branch symptoms will not recede while the root essence is first depleted. Once the root is depleted, expelling pathogens becomes even harder, leading to worsening over time. These practitioners still fail to reflect, administering more decoctions, making the condition incurable. However, hot medicines are also inappropriate. If it is a Fire syndrome, applying hot substances is like pouring oil on a fire, making the flames fiercer. Some have a preference for pungent-warm properties and fear/loathe cool-cold herbs; their skills are far superior to those of mediocre physicians. Regarding raw versus cooked herbs: Raw herbs are fierce in nature and thin in flavor, acting rapidly; they are used in dispersing formulas to specialize in attacking pathogens. Cooked herbs are mellow in nature and rich in flavor, acting slowly; they are used in tonifying formulas to leverage their supportive power. Market physicians with insufficient resources often pick fresh flowers for emergencies, ignoring that herbs have specific geographical origins (Dao-di). If not recorded in the Materia Medica, the name is incorrect, and Dao-di origin cannot be established. Even if compliant, it is not the royal way. If herb qi is biased, can organ qi not become extremely imbalanced? Some dislike raw herbs, preferring elaborate cooking. One must know that herbs have aroma and flavor; excessive processing alters these and destroys the essence, leaving only dead residue. With such diminished potency, how can treatment succeed? Furthermore, sour and salty flavors do not ascend, sweet and warm do not descend, bitter and cold do not float, pungent and hot do not sink; this is their nature. Ascending herbs mixed with salty-cold agents descend directly to the lower Yuan. Sinking herbs mixed with ginger and wine float up to the vertex. Nature resides in the herb, but application lies with the human. Thus, just as multiple fortifications around the capital require virtue and military display to achieve peace, and unified rule requires law and ritual education to foster benevolence and courtesy, so too is medicine like commanding troops and preparation like adjudicating cases. Crude practitioners ignore this entirely, mishandling raw/cooked and cold/hot balances, rarely avoiding fatal errors. Alas!