{"id":4260,"date":"2024-09-25T07:57:33","date_gmt":"2024-09-25T07:57:33","guid":{"rendered":"https:\/\/www.osmosis.org\/blog\/?p=4260"},"modified":"2025-10-01T11:38:23","modified_gmt":"2025-10-01T19:38:23","slug":"usmle-step-1-question-of-the-day-blurry-vision","status":"publish","type":"post","link":"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision","title":{"rendered":"USMLE\u00ae Step 1 Question of the Day: Blurry vision"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_80 ez-toc-wrap-center counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">In This Article<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\/#The_correct_answer_to_todays_USMLE%C2%AE_Step_1_Question_is%E2%80%A6\" >The correct answer to today&#8217;s USMLE\u00ae Step 1 Question is&#8230;<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\/#Incorrect_Answer_Explanations\" >Incorrect Answer Explanations<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\/#Main_Explanation\" >Main Explanation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\/#Major_Takeaway\" >Major Takeaway<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\/#References\" >References<\/a><\/li><\/ul><\/nav><\/div>\n\n<p class=\"wp-block-paragraph\"><em><strong>Prepare for the USMLE Step 1 exam with this detailed question about a 39-year-old woman experiencing progressive visual changes and muscle weakness. Do you know the answer? Let&#8217;s find out!<\/strong><\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A 39-year-old woman comes to her primary care physician for evaluation of visual changes. She reports having blurry vision that is more pronounced at the end of the day. The symptom started gradually around 3 months ago and has been progressing over time. The patient was recently diagnosed with an anterior mediastinal mass via chest CT. She consumes a diet rich in fresh vegetables and meats. Her temperature is 37.0\u00b0C (98.6\u00b0F), pulse is 67\/min and blood pressure is 118\/75 mmHg. Physical examination reveals weakness in the extraocular muscles. When the patient is asked to look upwards toward the ceiling for 60 seconds, she notes double vision after 40 seconds, which resolves after several minutes of rest. Visual acuity and pupillary reflexes are normal. The remainder of the physical examination is unremarkable.&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/neuromuscularjunction.png\" alt=\"MOTOR NERVE\nStructure A\nStructure B\nStructure D\nStructure E\nshowing an interaction with\nStructure C\nMuscle Fiber\"\/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Which of the following structures at the neuromuscular junction is <em>most likely<\/em> affected in this patient\u2019s condition?\u00a0<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.&nbsp;Structure A<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B.&nbsp;Structure B<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.&nbsp;Structure C<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D.&nbsp;Structure D<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.&nbsp;Structure E<\/strong><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><em>Scroll down for the correct answer!<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"The_correct_answer_to_todays_USMLE%C2%AE_Step_1_Question_is%E2%80%A6\"><\/span>The correct answer to today&#8217;s USMLE\u00ae Step 1 Question is&#8230;<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.\u00a0Structure C<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Before we get to the Main Explanation, let&#8217;s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Incorrect_Answer_Explanations\"><\/span>Incorrect Answer Explanations<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.\u00a0Structure A<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;This patient with ptosis, diplopia and extraocular muscle weakness most likely has MG, which occurs due to the formation of auto-antibodies against postsynaptic ACh receptors. In contrast, structure A is a presynaptic mitochondria, which plays no role in the pathogenesis of MG.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>\u00a0B.\u00a0Structure B<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;Structure B is a presynaptic vesicle containing ACh. Botulinum toxin works by inhibiting extravasation of these vesicles into the synaptic cavity, thereby inhibiting the release of ACh. Clinically, it can manifest as diplopia, dysarthria, dysphagia, and dyspnea. It is unlikely in this patient without any risk factors (e.g. ingestion of expired canned foods).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D.\u00a0Structure D\u00a0<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Structure D is a presynaptic calcium channel. Patients with Lambert Eaton myasthenic syndrome develop auto-antibodies against this structure. The condition manifests with muscle weakness that temporarily improves with activity. However, this patient has ptosis that is elicited by prolonged upwards gaze, which suggests that her muscle weakness is worsened with activity. This finding is more consistent with MG.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.\u00a0Structure E<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;Structure E is a vesicle that has fused with the cellular membrane and is releasing ACh into the neuromuscular junction. As mentioned before, botulinum toxin impairs this process and can manifest with flaccid muscle paralysis, diplopia, dysarthria, and\/or dysphagia.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Main_Explanation\"><\/span>Main Explanation<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The patient has&nbsp;extraocular muscle weakness&nbsp;that&nbsp;worsens&nbsp;with repeated activity and improves with rest. These findings are concerning for&nbsp;myasthenia gravis (MG). MG is often associated with thymic abnormalities (e.g., thymic hyperplasia or&nbsp;thymoma), as seen in this patient with recent diagnosis of mediastinal mass on CT scan.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">MG is a&nbsp;type II hypersensitivity&nbsp;reaction that develops when B-cells begin producing antibodies against&nbsp;nicotinic acetylcholine&nbsp;(ACh)&nbsp;receptors&nbsp;on muscle cells. Myasthenia gravis causes muscle weakness via two mechanisms. First, the antibodies block the binding of ACh to its receptors. Second, the antibodies can activate the&nbsp;classical complement pathway, resulting in destruction of ACh receptors.&nbsp;&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Due to the reduced number of available ACh receptors,&nbsp;ACh released at the nerve terminal is unable to generate the postsynaptic potential needed to induce muscle contraction, resulting in muscle weakness. The weakness is more pronounced with the repeated use of a muscle group, since it causes depletion of the ACh store in the neuromuscular junction.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">A minority of people with MG produce another type of antibody against&nbsp;muscle-specific tyrosine kinase&nbsp;(MuSK). This antibody attacks proteins within myocytes and also results in impaired muscle cell activity.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Major_Takeaway\"><\/span>Major Takeaway<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">MG is a&nbsp;type II hypersensitivity&nbsp;reaction that is most commonly caused by the production of auto-antibodies against&nbsp;nicotinic ACh receptors. The antibodies prevent the binding of ACh to its receptors and cause complement-mediated receptor destruction. A minority of cases are caused by the production of auto-antibodies against&nbsp;MuSK.&nbsp;&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"References\"><\/span>References<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Melzer, N., Ruck, T., et al. (2016) Clinical features, pathogenesis, and treatment of myasthenia gravis: A supplement to the Guidelines of the German Neurological Society.&nbsp;Journal of Neurology. 263, 1473-1494. Doi: 10.1007\/s00415-016-8045-z.&nbsp;<\/li>\n\n\n\n<li>Pasnoor, M., Dimachkie, M.M., Farmakidis, C., Barohn, R.J. (2018) Diagnosis of myasthenia gravis.&nbsp;Neurologic Clinics. 36(2), 261-274. Doi: 10.1016\/j.ncl.2018.01.010.&nbsp;<\/li>\n\n\n\n<li>Trouth, A.J., Dabi, A., et al. (2012) Myasthenia gravis: A review.\u00a0Autoimmune Diseases. 874680. Doi: 10.1155\/2012\/874680.\u00a0<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image\"><a href=\"https:\/\/www.osmosis.org\/ultimate-guide\/usmle-step-1\" target=\"_blank\" rel=\"noreferrer noopener\"><img decoding=\"async\" src=\"https:\/\/osmose-it.s3.amazonaws.com\/IEVwkP8WQJe3hUkVpLPWPGOTRBqGDF-v\/_.png\" alt=\"Osmosis sign up ad\"\/><\/a><figcaption class=\"wp-element-caption\"><em><em><sub>The United States Medical Licensing Examination (USMLE\u00ae) is a joint program of the Federation of State Medical Boards (FSMB\u00ae) and National Board of Medical Examiners (NBME\u00ae). Osmosis is not affiliated with NBME nor FSMB.\u00a0<\/sub><\/em><\/em><\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><em><strong>Want more USMLE\u00ae Step 1 practice questions? Try Osmosis by Elsevier today! Access your\u00a0<em><strong><a href=\"https:\/\/www.osmosis.org\/login?type=create\" target=\"_blank\" rel=\"noreferrer noopener\">free trial<\/a><\/strong><\/em>\u00a0and find out why millions of current and future clinicians and caregivers love learning with us.<\/strong><\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Test your knowledge with a USMLE Step 1 question on a patient with progressive blurred vision and muscle weakness linked to a mediastinal mass. Which neuromuscular structure is affected?<\/p>\n","protected":false},"author":202,"featured_media":4261,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[27,20,16,1366,1369,44],"tags":[1236,1238,1239,1241,1240,1242,1237,1244,1243,664],"class_list":["post-4260","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-medicine","category-exam-prep","category-do","category-questions","category-step-1-questions","category-step-1","tag-acetylcholine-receptor","tag-anterior-mediastinal-mass","tag-autoimmune-disease","tag-autoimmune-neurology","tag-extraocular-muscle-weakness","tag-mg-diagnosis","tag-myasthenia-gravis","tag-neurology-education","tag-neuromuscular-junction","tag-usmle-step-1"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v23.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>USMLE\u00ae Step 1 Question of the Day: Blurry vision - Osmosis Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-1-question-of-the-day-blurry-vision\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"USMLE\u00ae Step 1 Question of the Day: Blurry vision - Osmosis Blog\" \/>\n<meta property=\"og:description\" content=\"Test your knowledge with a USMLE Step 1 question on a patient with progressive blurred vision and muscle weakness linked to a mediastinal mass. 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