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The red filaments within the eye are the root of the nebula (corneal opacity/scarring), and the nebula is the sprout of the red filaments. When red filaments fill the eye, they each correspond to specific meridians. If one does not follow the meridian patterns and indiscriminately uses medicines to dissipate opacities, there will be no effect.

For instance, if the opacity develops from the inner canthus outward, it is a disease of the Hand-Taiyang (Small Intestine) and Foot-Taiyang (Bladder) meridians; one should take Qianghuo Shengfeng Tang (Notopterygium Decoction for Overcoming Wind) with added Cangzhu (Atractylodis Rhizoma) and Manjingzi (Vittatis Fructus). If the opacity enters from the lateral acute angle and extends obliquely downward toward the Kerenren acupoint (area anterior to the ear), it is a disease of the Foot-Shaoyang (Gallbladder), Hand-Shaoyang (Sanjiao), and Hand-Taiyang (Small Intestine) meridians; add Longdancao (Gentianae Radix), Gaoben (Ligustici Rhizoma et Radix), and Renshen (Ginseng Radix). If the opacity descends along the ocular blood vessels, it is a disease of the Foot-Jueyin (Liver) and Hand-Shaoyin (Heart) meridians; double the dosage of Chaihu (Bupleuri Radix) and Huanglian (Coptidis Rhizoma). If the opacity ascends from below to above the limbus, it is a disease of the Hand-Taiyang (Small Intestine) meridian; add Wuweizi (Schisandrae Chinensis Fructus) and Mutong (Akebiae Caulis). By adjusting prescriptions according to the meridians, efficacy will naturally follow immediately.

To eliminate the nebula, one must first dissipate the red filaments. Observe which meridian's red filament appears first, and begin treatment on those appearing later. Red filaments present for three years appear purplish-red; those present for two years appear wood-red (dark brown); those present for one year appear bright red. First dissipate the bright red, then the wood-red, and finally the purplish-red. Treating according to the meridians yields miraculous results. The formula for Shengfeng Tang is found in Zhenren's *Mijue* (Secrets). Since both nebula and red filaments are present, use the blowing method (blowing medicinal powder into the eye) and dropping method (applying eye drops) from *Mijue*.

When the eye suddenly erupts with swelling, pain, and burning heat, before red filaments and nebula have formed, it is appropriate to promote urination and defecation. This allows the fire pathogen to exit through the urine and stool, providing an outlet so that fire does not attack upward to the eye, thereby curing the disease. However, once red filaments and nebula have already formed, if one hastily uses cold-natured medicines to promote urination and defecation, the coldness will freeze and solidify the nebula, turning it into an entrenched and difficult-to-cure condition. It is often seen that practitioners treating eye diseases, regardless of whether opacities exist, immediately use purgative formulas to drain fire. This damages the stomach and spleen with coldness, prevents the vital energy from ascending, and gives rise to various ailments, let alone merely failing to resolve the nebula? Initially use Lizhi Gao (Pear Juice Ointment), subsequently use Baiyu Ding (White Jade Tablet), and finally use Saowu Dan (Fog-Sweeping Elixir) as eye drops.

The classics state: "The eye sees only when nourished by blood," meaning that the essence of blood flows upward to the eye to provide clarity. In chronic diseases, overuse of cold-natured medicines damages the stomach and spleen; overuse of dispersing medicines depletes the essence. This leads to stagnation of qi and blood, causing the nebula to persist. In treating nebula resulting from old age or long duration, one must first tonify qi and nourish blood. When qi and blood are sufficient, the nebula naturally becomes mobile and easy to dissipate. Insufficient blood means the eye lacks nourishment; excessive fire consuming blood also means the eye lacks nourishment. In such cases, topical application is not suitable.