As the saying goes: “Eyes never get enough of seeing, and stomachs never get enough of eating.” Everyone knows that eyes are important visual organs, and as the saying goes, “Without eyes, one is blind,” which is why we say “blind eye” when referring to a misjudgment of someone. So how does Traditional Chinese Medicine (TCM) view the eyes? Do they have other functions akin to a lens for observation?
According to TCM, the eyes not only have visual functions but can also be used to observe the health status of internal organs, diagnosing many ophthalmic diseases. As it is said, “The essence of the five zang and six fu organs all rise up to the eyes, providing their essence,” “The eyes are messengers of the heart,” “The essence of the gallbladder is the white of the eye, the essence of muscles is the ligament, wrapping and gathering the essence of tendons, bones, blood, and qi, and together with the pulse form a system, connecting upward to the brain.” This unique method of observing the eyes for diagnosis is called the Five-Wheel Differentiation. The Five-Wheel Differentiation uses the theory of the five elements and the theory of zang-fu organs to divide the eye into five positions: the flesh wheel, blood wheel, qi wheel, wind wheel, and water wheel, corresponding to the spleen, heart, lung, liver, and kidney respectively. “Wheel” literally means round. The eyelid, pupil, iris, anterior sclera, vitreous body, etc., are all round or spherical, so through the TCM thinking of “image, idea, response,” each part of the eye is divided into a “wheel”; secondly, the word “wheel” implies rotation, movement, and flexibility, and the eyes are known as the “residence of spirit and clarity” and “the organ of vision,” so using “wheel” to understand the eyes and apply it throughout the physiology, pathology, and diagnosis of ophthalmic diseases is most appropriate. Let's take a closer look at the unique Five-Wheel Differentiation in TCM ophthalmology.
Flesh Wheel
The flesh wheel corresponds to the eyelid and conjunctiva. Since the spleen governs flesh, the flesh wheel is attributed to the spleen. The main function of the flesh wheel is to control the opening and closing of the eyelids, protect the eyeball, and nourish it. The opening and closing of the eyelids, one up and one down, is just like the spleen rising and the stomach descending, and the spleen and stomach are the hub of the body's ascending and descending qi. Therefore, from the perspective of the movement characteristics of the flesh wheel, the spleen and stomach are closely related to the physiology and pathology of the eyelids. Conversely, abnormal changes in the flesh wheel can also reflect the physiological and pathological state of the spleen and stomach.
Clinically, flesh wheel differentiation is often used for eyelid diseases. For example, redness, swelling, and erosion of the eyelids are often caused by damp-heat in the spleen and stomach, disturbing the eyelids; a stye can be caused by residual pathogenic factors and latent heat in the spleen and stomach; chalazion (meibomian gland cyst) is often due to spleen dysfunction and accumulation of phlegm-dampness; blepharitis is often caused by damp-heat in the spleen and stomach and exposure to wind pathogen; eyelid twitching is often caused by deficiency of both heart and spleen, blood deficiency in the liver and spleen, and wind arising from blood deficiency; and ptosis is often related to spleen qi deficiency and sinking of central qi.
Blood Wheel
The blood wheel corresponds to the inner and outer canthus of the eye, including the caruncle, semilunar fold, upper and lower tear points, and vessels in the canthus. Since the heart governs blood and vessels, the blood wheel is attributed to the heart. Therefore, lesions of the blood wheel are often related to the heart and small intestine. The caruncle belongs to the blood wheel, and the tears it secretes have the effect of nourishing the eyeball. Therefore, in clinical practice, tearing disorders are often due to deficiency of both qi and blood, and can be treated by methods that tonify qi and nourish blood to stop tears. Acute dacryocystitis is often caused by heat accumulation in the heart channel and exuberant heat-toxin in the heart and spleen.
It should be noted that since the liver governs tears and the kidney governs water, diseases of the canthus are often related to the liver and kidney. In clinical practice, treatment should be based on actual conditions and differentiated syndromes.
Qi Wheel
The qi wheel corresponds to the sclera, anterior sclera, and bulbar conjunctiva, commonly known as the “white of the eye.” Since the lung governs qi and respiration and is associated with the color white, lesions of the qi wheel are often related to the lung and large intestine. Clinically, many diseases of the white of the eye, such as pterygium, subconjunctival hemorrhage, and epidemic keratoconjunctivitis, are often related to invasion by wind-heat, heat accumulation in the lung channel, damp-heat with wind, and heat causing blood to run amok in the lung. Clinically, symptoms often include redness of the white of the eye, eye pain and itching, grittiness and burning sensation, and treatment should focus on dispersing wind-heat, clearing fire and detoxifying, cooling blood and reducing redness, and regulating the bowels. If there is a deficiency pattern, then nourishing the lung and yin, and tonifying qi and generating body fluids should be considered.
Wind Wheel
The wind wheel corresponds to the cornea and the black of the eye except for the central pupil. Since the liver is the organ of wind-wood, lesions of the cornea are often related to the liver and gallbladder. The wind wheel is exposed externally, and in terms of the plane of the eye, it is located relatively higher, therefore, the wind wheel is most susceptible to external pathogens and toxins, being injured by wind-heat or affected by disease transmission from other wheels.
Clinically, the incidence rate of corneal diseases is high, mainly including herpetic keratitis, bacterial keratitis, and fungal keratitis. Common clinical manifestations include many small star-shaped opacities gathered in the black of the eye (positive fluorescein staining test), decreased vision, gritty and burning sensation, photophobia and tearing, and in severe cases, constriction of the pupil, pus in the anterior chamber, corneal rupture and collapse leading to blindness. Corneal diseases are often caused by exuberant liver fire, wind-heat in the liver meridian, yin deficiency of the liver and kidney, damp-heat in the liver and gallbladder, and exposure to wind-heat. Therefore, treatment should focus on clearing liver fire, dispelling wind and heat, nourishing yin and clearing heat, and removing opacities and improving vision.
Water Wheel
The water wheel corresponds to the pupil and intraocular tissues. Since the kidney governs water and the pupil is the deepest part, lesions of the pupil and intraocular tissues are often related to the kidney, and because essence and blood share the same origin, they are also often related to the liver.
Clinically, acute anterior uveitis, iridocyclitis can be caused by yin deficiency of the liver and kidney, leading to virtual fire rising and scorching the iris; chronic anterior uveitis is often caused by yang deficiency of the spleen and kidney, failing to vaporize fluid upwards, resulting in dryness and an irregularly shaped pupil.
Secondly, the pathological color changes of the water wheel are more varied than those of other wheels. For example, redness of the pupil is often due to bleeding in the fundus; a pale green pupil accompanied by narrowing of the visual field is often seen in primary open-angle glaucoma; whitening of the pupil is often cataract; yellowing of the pupil is often seen in intraocular tumors such as retinoblastoma, retinal detachment, vitreous proliferation, vitreous abscess, etc.
In addition, we can also diagnose some internal ocular diseases by observing the pupil. However, due to the lack of modern technology in ancient times, modern TCM practitioners need to use fundus photography and ophthalmoscopy for examination if they suspect internal ocular lesions after observing the pupils.