An Indian eye-surgery book vanished from China. Korea kept part of it. The operation was cataract couching: a needle goes in beside the white of the eye and pushes the clouded lens out of the way. The Sushruta Samhita describes the Indian procedure. By the Tang dynasty it was in Chinese medicine, taught under the name of one book, the Longshu pusa yanlun, "Bodhisattva Nagarjuna's eye treatise". In 752 Wang Tao's Waitai miyao already quotes an older Indian treatise on the eye. Then the trail breaks. The original Longshu book was not handed down in China. A large part of it was copied into Korea's great medical compendium Uibang yuchwi, compiled under King Sejong in 1445. It has 8 sections and 30 eye diseases. It names heat and wind as main causes. It says the cataract forms when poison and heat gather in the brain and the eye's "oil" runs down over the pupil. And it gives the golden-needle method step by step, to be done only when the film has hardened "like white jade". Korean scholars Kim and Kang call it a record of Indian medical ideas already lost in China. An operation travelled from India to China. The Chinese copies of the book were lost. A Korean encyclopedia kept the text. 🙏🙏 Sources: Wang Tao, Waitai miyao (752); Yi fang lei ju vol. 64 (Joseon); Kim & Kang, Korean J. Med. Hist. 22(1), 2013; Deshpande, Bull. SOAS (1999) Photo 1: Cataract couching in India (painting, undated). Wellcome Library, London, CC BY 4.0 Photo 2: Uibang yuchwi, volume 201 cover (Joseon, 1477 per Commons). Public domain, via Wikimedia Commons