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In human life, the ears are responsible for hearing and the eyes for vision; thus, among the five sense organs, the eyes and ears play the predominant roles. Comparing the two, the eyes are even more critical. Why? For one who is blind in the eyes but uses the ears to substitute for vision becomes an invalid, whereas one whose hearing is not acute but whose vision is clear and can also listen remains a whole person. In ancient times, Yan Di (Shennong, the Divine Farmer) pitied the suffering of the people from epidemics and premature death. He gathered fruits of herbs and trees, tasted them carefully, distinguished their properties of cold, warm, dry, and hot, identified the appropriate roles of sovereign, minister, assistant, and courier in prescription formulation, and compiled medical texts. When the people suffered from diseases, medicines brought immediate recovery. Yet why did this text neglect the treatment of eye diseases? It was likely that in ancient times, desires had not yet proliferated, preserving life was favorable, and eye diseases were extremely rare. Later, as knowledge expanded, the mind was agitated internally, and essence was exhausted externally. Heart disease leads to blood failing to nourish the eyes; kidney disease causes dimness of the pupils; lung pathology results in increasing blood vessels on the sclera (white part of the eye); liver disorders lead to the formation of corneal opacities or membranes. These are all caused by emotional desires, initially unnoticed, accumulating over time until vision dims, at which point the source of eye disease is recognized. Alas! The livelihood of the people relies primarily on unobstructed paths, akin to asking if such conditions existed in the time of Yan Di. Therefore, many books omit this topic, not out of negligence. Sun Simiao (Sun Zhenren) wrote "Secrets of Ophthalmology" to supplement the deficiencies in Yan Di's medical texts, but its original manuscripts were often kept secret and failed to spread widely. Yu Cong, in his youth, studied hard and injured his eyes through overuse; physicians could not cure him. He prayed to the City God (Chenghuang), received four volumes of a book in a dream, and upon waking, encountered a manuscript transmitted by Wang Fuwan, which matched the dream exactly. Cong applied the prescriptions found therein, and his eyes recovered. For others with eye diseases, he diagnosed the specific etiology and treated them, achieving universal cures. Cong then compiled "Chan Wei" (Elucidating Subtleties) and "Ru Men" (Introduction) to transmit to the world and future generations, having them printed via woodblock printing by Feng Suikun and others. Alas! With the publication of this book, how could it be inferior to Yan Di's medical texts? I served in official posts for over thirty years, burdened by complex administrative documents, leading to eye strain and mental fatigue, resulting in poor vision. Cong medicated me, restoring my vitality; this is Cong's merit. Now that Cong is old, fortunately, his book has been preserved. I wish that readers of this book will treasure it as they would medical texts and never forget Cong's contributions, thereby expressing deep gratitude.
Preface written on the first auspicious day of the spring of Xinsi year in the Kangxi reign by Wang Jichang, Gentleman Attendant of Benzhi (Fengzhi Dafu), Prefect of Jiaozhou, from Pingling.