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</div><div><span>Refraction</span></div></div>
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<article><div id="d-article"><div class="page-info"><div class="page-title"><a name="start" id="start">
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</a><h1 class="with-also" itemprop="name">Refraction</h1>
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</noscript></div><div class="main"><div id="ency_summary"><p>A refraction is an eye exam that measures a person's prescription for eyeglasses or contact lenses.</p></div><section><div class="section"><div class="section-header"><div class="section-title"><h2>How the Test is Performed</h2></div><div class="section-button"><button type="submit" aria-controls="section-1" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-1"><p>This test is performed by an ophthalmologist or optometrist. Both of these professionals are often called an "eye doctor."</p><p>You sit in a chair that has a special device (called a phoroptor or refractor) attached to it. You look through the device and focus on an eye chart 20 feet (6 meters) away. The device contains lenses of different strengths that can be moved into your view. The test is performed one eye at a time.</p><ul><li>The eye doctor will then ask if the chart appears more or less clear when different lenses are in place.The results depend on your responses.</li><li>Then, a device shines specialized light into your eyes and also determines your refraction. Responses from you are not needed. Each type of refraction has their own benefits.</li></ul></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>How to Prepare for the Test</h2></div><div class="section-button"><button type="submit" aria-controls="section-2" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-2"><p>If you wear contact lenses, ask the doctor if you need to remove them and for how long before the test.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>How the Test will Feel</h2></div><div class="section-button"><button type="submit" aria-controls="section-3" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-3"><p>There is no discomfort.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>Why the Test is Performed</h2></div><div class="section-button"><button type="submit" aria-controls="section-4" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-4"><p>This test can be done as part of a <a test="test" href="./003434.htm">routine eye exam</a>. The purpose is to determine whether you have a refractive error (a need for glasses or contact lenses).</p><p>For people over age 40 who have normal distance vision but difficulty with near vision, a refraction test can determine the right power of reading glasses.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>Normal Results</h2></div><div class="section-button"><button type="submit" aria-controls="section-5" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-5"><p>If your uncorrected vision (without glasses or contact lenses) is normal, then the refractive error is zero (plano) and your vision should be 20/20 (6/6).</p><p>A value of 20/20 (6/6) is normal vision. This means you can read 3/8-inch (1 centimeter) tall letters at 20 feet (6 meters). A small type size is also used to determine normal near vision.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>What Abnormal Results Mean</h2></div><div class="section-button"><button type="submit" aria-controls="section-6" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-6"><p>You have a refractive error if you need a combination of lenses to see 20/20 (6/6). Glasses or contact lenses should give you good vision. If you have a refractive error, you have a "prescription." Your prescription is a series of numbers that describe the powers of the lenses needed to make you see clearly.</p><p>If your final vision is less than 20/20 (6/6), even with lenses, then there is probably another, non-optical problem with your eye.</p><p>The vision level you achieve during the refraction test is called the best-corrected visual acuity (BCVA).</p><p>Abnormal results may be due to:</p><ul><li><a test="test" href="./001015.htm">Astigmatism</a> (abnormally curved cornea causing blurred vision)</li><li><a test="test" href="./001020.htm">Hyperopia</a> (farsightedness)</li><li><a test="test" href="./001023.htm">Myopia</a> (nearsightedness)</li><li><a test="test" href="./001026.htm">Presbyopia</a> (inability to focus on near objects that develops with age) </li></ul><p>Other conditions under which the test may be performed:</p><ul><li><a test="test" href="./001032.htm">Corneal ulcers and infections</a></li><li>Loss of sharp vision due to <a test="test" href="./001000.htm">macular degeneration</a></li><li><a test="test" href="./001027.htm">Retinal detachment</a> (separation of the light-sensitive membrane (retina) in the back of the eye from its supporting layers)</li><li><a test="test" href="./001028.htm">Retinal vessel occlusion</a> (blockage in a small artery that carries blood to the retina)</li><li><a test="test" href="./001029.htm">Retinitis pigmentosa</a> (an inherited disorder of the retina)</li></ul></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>Risks</h2></div><div class="section-button"><button type="submit" aria-controls="section-7" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-7"><p>There are no risks with this test.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>Considerations</h2></div><div class="section-button"><button type="submit" aria-controls="section-8" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-8"><p>You should have a complete eye examination every 3 to 5 years if you have no problems. If your vision becomes blurry, worsens, or if there are other noticeable changes, schedule an exam right away.</p><p>After age 40 (or for people with a family history of <a test="test" href="./001620.htm">glaucoma</a>), eye exams should be scheduled at least once a year to test for glaucoma. Anyone with diabetes should also have an eye exam at least once a year or as recommended by their provider.</p><p>People with a refractive error should have an eye exam every 1 to 2 years, or when their vision changes.</p></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>Alternative Names</h2></div><div class="section-button"><button type="submit" aria-controls="section-Alt" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-Alt"><p>Eye exam - refraction; Vision test - refraction; Refraction</p></div></div></section><section><div class="section sec-mb"><div class="section-header"><div class="section-title"><h2>Images</h2></div><div class="section-button"><button type="submit" aria-controls="section-tnails" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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<li><img src="//medlineplus.gov/ency/images/ency/tnails/9925t.jpg" alt="Normal vision" title="Normal vision" class="side-img"/><a href="../imagepages/9925.htm">Normal vision</a></li>
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</ul></div></div></section><section><div class="section"><div class="section-header"><div class="section-title"><h2>References</h2></div><div class="section-button"><button type="submit" aria-controls="section-Ref" role="button" title="Expand/Collapse section"><span class="icon icon-section-action">
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</div></div><div class="section-body" id="section-Ref"><p>Chuck RS, Dunn SP, Flaxel CJ; American Academy of Ophthalmology Preferred Practice Pattern Committee, et al. Comprehensive adult medical eye evaluation preferred practice pattern. <em>Ophthalmology</em>. 2021;128(1):1-29. <a href="https://www.aaojournal.org/article/S0161-6420(20)31026-5/fulltext" target="_blank">www.aaojournal.org/article/S0161-6420(20)31026-5/fulltext</a>. Published November 12, 2020.</p><p>Jacobs DS, Afshari NA, Bishop RJ, et al. Refractive errors preferred practice pattern. <em>Ophthalmology</em>. 2023;130(3):P1-P60. PMID: 36543603 <a href="https://pubmed.ncbi.nlm.nih.gov/36543603/" target="_blank">pubmed.ncbi.nlm.nih.gov/36543603/</a>.</p><p>Jacobs DS, Lee JK, Shen TT, et al. Refractive surgery preferred practice pattern. <em>Ophthalmology</em>. 2023;130(3):P61-P135. PMID: 36543604 <a href="https://pubmed.ncbi.nlm.nih.gov/36543604/" target="_blank">pubmed.ncbi.nlm.nih.gov/36543604/</a>.</p><p>Wu A. Clinical refraction. In: Yanoff M, Duker JS, eds. <em>Ophthalmology</em>. 6th ed. Philadelphia, PA: Elsevier; 2023:chap 2.3.</p></div></div></section>
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