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What Lies Beneath

2022; Lippincott Williams & Wilkins; Volume: 44; Issue: 5 Linguagem: Inglês

10.1097/01.eem.0000831228.50941.58

1552-3624

Michelle Johnston,

Figure: tears, physiology, anatomyFigureThere are said to be three main types of tears. Not long ago I saw a string of patients with all three within a few short hours of each other in the ED, and I thought, there's a column in that. Before we break down this triumvirate of epiphora, let us take a brief tour through the physiology of tears. We are traditionally taught that tears are produced by the lacrimal gland, but the truth is so much more complex. Also in tripartite organization, tears consist of three layers—an outer lipid layer secreted by the gangster-sounding glands of Zeis and Moll in addition to the numerous meibomian glands, a middle aqueous layer formed within the main lacrimal gland but with contributions from the more Germanic-sounding glands of Krause and Wolfring, and finally the inner mucous layer arising from the goblet cells, as well as the crypts of Henle and the glands of Manz. Who knows what they sound like? All I know is a deeply intricate system of machinery allows us to weep. Marvelous Tears Of course, tears do much more. The first of the functions is basal tearing. This produces a steady layer of tears that coats the cornea and has myriad responsibilities: keeping the cornea moist, allowing gas exchange, cleaning debris from the transparent surface as well as providing an immunologic barrier, and maintaining a smooth optical surface for optimal focus. Marvelous! We produce about a gram of these lubricating babies every day, which slows as we age. Reflex tearing is the response to an irritant. Think onions, whose infamy lies in their sulphurous nature, that when cut asunder produce a nasty volatile cocktail of sulfenic acids and oxides. These trigger transient receptor potential channels in the ophthalmic nerve (V1), setting off tearing. The classic teaching is to keep your onions in the fridge until the moment of hewing to slow the action of the catalyst enzymes. Or you could simply do as I do and get someone else to chop the onions. Bright lights and hot sensations to the tongue can do the same. Emotional tearing is the weird one. Humans are the only mammals to do this, and we cry, as you well know, in response to a plethora of strong psychological stimuli (and the odd well-choreographed TV commercial). Tears produced by emotion have a very different chemical makeup from other tears, and they are a lot more proteinaceous. They look stunningly unique under an electron microscope. Emergency Pathologies When the tears are done, they gather in a gloriously named lacrimal lake, with a lacrimal papilla forming a small elevation on the edge of the lacrimal lake. The tears continue down the tributaries through the aqueducts. It all sounds so bucolic, an emotional place, lined with weeping willows, although they do end up in the less gentrified nasal cavities. Not too many emergency pathologies of the lacrimal apparatus face us in the ED, but we should be aware of a few: Injury to the nasolacrimal duct: Dog bites figure disproportionately highly. These are usually complex, and almost universally require referral to an ophthalmologist for repair to prevent a lifetime of universal weeping. Dacryocystitis: A result of obstruction of the nasolacrimal duct, with stagnating tears getting secondarily infected, forming an abscess that also requires operative management (the unsnappily named dacryocystorhinostomy) as well as antibiotics. Sjögren syndrome: A chronic autoimmune condition attacking the secretory glands of the mouth and eyes. It is commonly associated with systemic sclerosis, systemic lupus erythematosus, or rheumatoid arthritis. Keratoconjunctival sicca can result in significant corneal pathology, including ulcers. Tear pathology needs to be taken seriously because we can condemn our patients to a lifetime of scarcity or surplus if missed. We need optimally functioning tears for ocular longevity, although the great British band of the 1980s, Tears for Fears, would like to tell us: All for freedom and for pleasure / Nothing ever lasts forever / Everybody wants to rule the world. Share this article on Twitter and Facebook. Access the links in EMN by reading this on our website: www.EM-News.com. Comments? Write to us at [email protected]. Dr. Johnstonis a board-certified emergency physician, thus the same as you but with a weird accent. She works in a trauma center situated down the unfashionable end of Perth, Western Australia. She is the author of the novel Dustfall, available on her website, http://michellejohnston.com.au/. She also contributes regularly to the blog Life in the Fast Lane athttps://lifeinthefastlane.com. Follow her on Twitter@Eleytheriusand read her past columns athttp://bit.ly/EMN-WhatLiesBeneath.