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The *Jiyao* (Essential Principles) states: When the disease is in the Fu organs, it belongs to the Exterior level; one should dispel Wind and dissipate Heat. When the disease is in the Zang organs, it belongs to the Interior level; one should nourish Blood and calm the Spirit. Acute onset indicates an Exterior condition, which is easy to treat; chronic duration indicates an Interior condition, which is difficult to cure.

Zihe (Zhang Congzheng) said: Although the Sages stated that "the eyes can see when they receive Blood," there are also conditions of Blood excess and deficiency. Excess leads to obstruction in the eyes causing pain; deficiency leads to exhaustion of the eyes causing blindness. Therefore, young people mostly exhibit Blood excess, while old people mostly exhibit Blood deficiency. However, young people generally do not have Blood deficiency; among old people, some still exhibit Blood excess, which must be carefully observed. The inner canthus (Neican) is where the Foot-Taiyang Bladder Meridian begins; here, Blood is abundant and Qi is scarce. The outer canthus (Waican) is where the Foot-Shaoyang Gallbladder Meridian resides; here, Blood is scarce and Qi is abundant. The upper eyelid (Shanggan) belongs to the Foot-Taiyang Bladder Meridian, where Blood is abundant and Qi is scarce. The lower eyelid (Xiagan) belongs to the Foot-Yangming Stomach Meridian, where both Blood and Qi are abundant. However, the Foot-Yangming Stomach Meridian originates at the intersection beside the eyes and converges with the Taiyang and Shaoyang meridians at the eyes. Only the Foot-Jueyin Liver Meridian connects to the eye system. Thus, Blood excess is a Fullness syndrome of the Foot-Taiyang and Foot-Yangming meridians; Blood deficiency is a Deficiency syndrome of the Foot-Jueyin meridian. Therefore, bloodletting is suitable for the Foot-Taiyang and Foot-Yangming meridians because these two meridians have abundant Blood. The Foot-Shaoyang meridian alone is unsuitable for bloodletting because its Blood is scarce. Pricking the Foot-Taiyang and Foot-Yangming meridians to bleed will make the vision clearer; pricking the Foot-Shaoyang meridian to bleed will make the vision dimmer. One must know not to cause excess or deficiency, but rather to nourish the eyes with Blood. Generally speaking, if Blood is too much, it overflows; if too little, it dries up. When the body is hot, Blood circulates rapidly and abundantly; when cold, it circulates slowly and sparingly; this is the general principle. The eyes are the external manifestation of the Liver. The Liver governs the eyes and belongs to Wood in the Five Elements. Although trees, as objects, if too lush become obstructive, if too withered become dry. The Five Wheels of the eyes are the essence of the Zang and Fu organs and the gathering place of the collaterals. The White Wheel (Sclera) belongs to Lung Metal; the Flesh Wheel (Eyelids) belongs to Spleen Earth; the Red Vessels belong to Heart Fire; the Black Water and Divine Light (Pupil and Vision) belong to Kidney Water, and also jointly belong to Liver Wood. This is known by common people. When eye diseases occur, however, people often do not understand the pathology. How can one say that eyes do not get sick without Fire? Why? If the White Wheel turns red, it is Fire invading the Lung; if the Flesh Wheel becomes red and swollen, it is Fire invading the Spleen; if the Black Water and Divine Light are obscured, it is Fire invading the Liver and Kidney; if red vessels penetrate the eye, it is Fire being excessive itself. To treat Fire, one sentence suffices. Thus, the *Neijing* says: "When Heat prevails, swelling occurs." All cases of sudden redness and swelling of the eyes, photophobia, heaviness, tearing, and sudden blurriness due to cold are caused by excessive Heat. The method to treat Fire involves using salty-cold herbs, employing emesis or purgation methods; in acupuncture, points such as Shenting (GV24), Shangxing (GV23), Xinhui (GV16), Qian Ding (GV20), and Baihui (GV20) are selected. For opacities, they can be cleared immediately; for pain, it can cease immediately; for dimness, clarity can return immediately; for swelling, it can subside immediately. However, children should not be needled at Xinhui (GV16) because the flesh is thin and bone is superficial, risking injury to the skull. Children have Water above and Fire below, so their vision is clear; old people have Fire above and insufficient Water, so their vision is dim. The *Neijing* says: "For Blood excess, one should drain it." Another classic states: "Deficiency is tonified, Fullness is reduced." Conditions like night blindness (Que Mu) inability to see at night, and internal cataracts caused by violent anger or great sorrow, result from the Liver governing the eyes and having deficient Blood; bloodletting is prohibited, and one should only tonify the Liver and nourish the Kidney. As for sudden redness and swelling, one should prick the aforementioned five points to bleed, then apply salt-oil to the hair roots. In severe cases, this may be repeated twice or three times. Measure the severity of the disease and aim for balance.

Commentary: This refers to the urgency of bloodletting for eye diseases, applicable to acute onset with heat and pain, or chronic conditions with severe stagnation, requiring venting via a three-edged needle. However, for elderly individuals, those with chronic deficiency, and those with Qi stagnation, using fine needles for tonification and reduction is appropriate. Thus, Zihe's words are a general guideline. For the Foot-Shaoyang meridian alone, bloodletting is unsuitable; one must avoid excess or deficiency, aiming only to nourish the eyes with Blood. This intent is evident.