{"id":1889,"date":"2026-10-20T08:51:40","date_gmt":"2026-10-20T08:51:40","guid":{"rendered":"https:\/\/laseristanbulclinic.com\/eye-tools\/eye-prescription-explained\/"},"modified":"2026-10-20T12:57:56","modified_gmt":"2026-10-20T12:57:56","slug":"eye-prescription-explained","status":"publish","type":"page","link":"https:\/\/laseristanbulclinic.com\/en\/eye-tools\/eye-prescription-explained\/","title":{"rendered":"Eye prescription reader"},"content":{"rendered":"<!-- Hero (Photo + summary card) Start -->\n<section class=\"page-hero\" id=\"top\">\n\t<div class=\"phero-inner pad with-media container-fluid\"><div class=\"row\">\n\t\t<div class=\"phero-left col-12 col-lg-7\">\n\t\t\t<div data-hero-in><ol class=\"crumbs\" aria-label=\"Breadcrumb\"><li><a href=\"https:\/\/laseristanbulclinic.com\/en\/\">Home: eye surgery in Istanbul<\/a><\/li><li><a href=\"https:\/\/laseristanbulclinic.com\/en\/eye-tools\/\">Free eye tools<\/a><\/li><li><span aria-current=\"page\">Eye prescription reader<\/span><\/li><\/ol><\/div>\t\t\t<h1 class=\"t64 hero-title phero-title\" data-lines>Online Eye Prescription Reader: Understand Sphere, Cylinder and Axis<\/h1>\n\t\t\t\t\t\t<p class=\"t22 phero-lead\" data-hero-in><strong>Before you start:<\/strong> have your latest prescription in front of you. It is the one your optician or eye doctor gave you after your last sight test, not the label on a box of lenses.<\/p>\n\t\t\t\t\t\t<div class=\"phero-ctas\" data-hero-in><a class=\"pill pill-white\" href=\"#tool\"><span class=\"pill-dot\" aria-hidden=\"true\"><\/span><span class=\"pill-label\">Read my prescription<\/span><\/a><\/div><ul class=\"phero-meta\" data-hero-in><li><svg width=\"16\" height=\"16\" aria-hidden=\"true\"><use href=\"#i-check\"\/><\/svg>Medically reviewed by <span class=\"ph\">{{surgeon}}<\/span> \u00b7 <span class=\"ph\">{{date}}<\/span><\/li><\/ul>\t\t<\/div>\n\t\t<div class=\"phero-right has-media col-12 col-lg-5\">\n\t\t\t\t\t\t<figure class=\"phero-media\" data-hero-in><img decoding=\"async\" width=\"640\" height=\"640\" src=\"https:\/\/laseristanbulclinic.com\/wp-content\/uploads\/2026\/10\/blue-eye-close-up.webp\" class=\"attachment-large size-large\" alt=\"Close-up of a blue eye\" fetchpriority=\"high\" srcset=\"https:\/\/laseristanbulclinic.com\/wp-content\/uploads\/2026\/10\/blue-eye-close-up.webp 1024w, https:\/\/laseristanbulclinic.com\/wp-content\/uploads\/2026\/10\/blue-eye-close-up-300x300.webp 300w, https:\/\/laseristanbulclinic.com\/wp-content\/uploads\/2026\/10\/blue-eye-close-up-150x150.webp 150w, https:\/\/laseristanbulclinic.com\/wp-content\/uploads\/2026\/10\/blue-eye-close-up-768x768.webp 768w\" sizes=\"(max-width: 640px) 100vw, 640px\" \/><\/figure>\n\t\t\t\t\t\t\t\t\t<div class=\"inshort\" data-hero-in><p>Use this free online eye prescription reader to see what your glasses prescription means. Each eye has a sphere (SPH) for short or long sight, a cylinder (CYL) and axis for astigmatism, and sometimes an ADD for reading, all in dioptres (D): minus means short-sighted, plus long-sighted. Want to be free of glasses? Prof. Dr. Ahmet Sat\u0131c\u0131 or Op. Dr. Aysan Bayram can tell you whether laser or lens surgery fits.<\/p><\/div>\n\t\t\t\t\t<\/div>\n\t<\/div><\/div>\n<\/section>\n<!-- Hero (Photo + summary card) End -->\n\n\n<!-- Eye Tool (Prescription reader) Start -->\n<section class=\"panel dark tool-panel\" id=\"tool\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\"><div class=\"tool-mount\" data-tool=\"rx\" data-lang=\"en\" data-consult=\"https:\/\/laseristanbulclinic.com\/en\/free-consultation\/\" data-eyetest=\"https:\/\/laseristanbulclinic.com\/en\/online-eye-test\/\" data-laser=\"https:\/\/laseristanbulclinic.com\/en\/laser-eye-surgery-turkey\/\" data-howto=\"#how-to-read-your-eye-prescription-uk-and-us-sph-cyl-axis-and\"><\/div><noscript><p class=\"t22\">This tool needs JavaScript. Please enable it, or ask a surgeon directly.<\/p><\/noscript><\/div><\/div><\/div><\/section>\n<section class=\"psec pad tight\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\"><div class=\"tool-after prose\"><p data-reveal><strong>Before you start:<\/strong> have your latest prescription in front of you. It is the one your optician or eye doctor gave you after your last sight test, not the label on a box of lenses.<\/p><\/div><\/div><\/div><\/div><\/section><!-- Eye Tool (Prescription reader) End -->\n\n\n<!-- FAQ (Question and answer rows) Start -->\n<section class=\"psec pad\" id=\"how-to-read-your-eye-prescription-uk-and-us-sph-cyl-axis-and\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\">\n\t\t<h2 class=\"t48 sec-title\" data-reveal>How to read your eye prescription (UK and US): SPH, CYL, AXIS and ADD<\/h2>\n\t\t\t<p class=\"t22 sec-lead\" data-reveal>Your prescription has one row per eye. The American Academy of Ophthalmology (AAO) explains the columns.<\/p>\n\t\t\t<div class=\"prose sec-pre\"><div class=\"tbl-wrap\" data-reveal><table class=\"tbl rsp\"><thead><tr><th scope=\"col\">Column<\/th><th scope=\"col\">What it tells you<\/th><th scope=\"col\">How to read it<\/th><\/tr><\/thead><tbody><tr><th scope=\"row\">OD \/ OS<\/th><td data-label=\"What it tells you\">Right eye and left eye<\/td><td data-label=\"How to read it\">Some practices write RE and LE; OU means both<\/td><\/tr><tr><th scope=\"row\">SPH (sphere)<\/th><td data-label=\"What it tells you\">The main lens power<\/td><td data-label=\"How to read it\">Minus means short-sighted, plus long-sighted<\/td><\/tr><tr><th scope=\"row\">CYL (cylinder)<\/th><td data-label=\"What it tells you\">Extra power for astigmatism<\/td><td data-label=\"How to read it\">Empty or 0 means none<\/td><\/tr><tr><th scope=\"row\">AXIS<\/th><td data-label=\"What it tells you\">Direction of the astigmatism<\/td><td data-label=\"How to read it\">A whole number from 1 to 180 degrees<\/td><\/tr><tr><th scope=\"row\">ADD<\/th><td data-label=\"What it tells you\">Extra power for near work<\/td><td data-label=\"How to read it\">Reading glasses, bifocals, varifocals<\/td><\/tr><tr><th scope=\"row\">Prism<\/th><td data-label=\"What it tells you\">Correction for double vision<\/td><td data-label=\"How to read it\">Measured in prism dioptres, with a base direction<\/td><\/tr><\/tbody><\/table><\/div><p data-reveal>Example: <strong>\u22122.00 \u22120.75 \u00d7 180<\/strong> means 2 dioptres of short sight and 0.75 dioptres of astigmatism along the 180\u00b0 (horizontal) line.<\/p><\/div>\n\t\t\t<div class=\"qa-list\">\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">What is a dioptre (diopter)?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>A dioptre (D; Americans write diopter) is the unit of lens power: one divided by the focal length in metres. Prescriptions go up in steps of 0.25 D.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">What does SPH (sphere) mean on an eye prescription?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>SPH is the main lens power. A minus number corrects short sight (myopia), where distant objects look blurred. A plus number corrects long sight (hyperopia), where near objects are harder to see. &#8220;Plano&#8221; means no sphere power. Your spherical equivalent is the sphere plus half the cylinder: \u22122.00 with \u22121.00 of cylinder is \u22122.50 D.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">What do cylinder (CYL) and axis mean?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>CYL corrects astigmatism, where the eye is shaped more like a rugby ball than a football, so light focuses in more than one place (NHS). The axis says in which direction the cylinder acts: 90 is vertical, 180 horizontal. The AAO says most people have 0.5 to 0.75 D of astigmatism, and 1.5 D or more typically needs correction.<\/p>\n<p data-reveal>Some practices write the cylinder with a plus sign, others with a minus; both describe the same lens. To switch, add sphere and cylinder, flip the cylinder&#8217;s sign and add 90 to the axis (subtract 180 if it passes 180). So \u22122.00 \u22121.00 \u00d7 180 equals \u22123.00 +1.00 \u00d7 90. The reader shows both.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">What do ADD, PD, prism and BVD mean?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal><strong>ADD<\/strong> is the near addition for presbyopia, which the AAO says typically becomes noticeable shortly after 40; your near power is sphere plus ADD. <strong>PD<\/strong> is the distance between your pupil centres. <strong>BVD<\/strong>, back vertex distance, is the gap between the back of the lens and the cornea, normally 12 to 14 mm. It matters above about \u00b14.00 D, because moving the lens changes the power reaching your eye, which is also why contact-lens prescriptions differ from glasses.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">Is a 1.50 eye prescription bad?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>No. A prescription measures the lens you need, not the health of your eyes. A sphere of \u22121.50 is low myopia: the international definition counts \u22120.50 D to just above \u22126.00 D as low, and \u22126.00 D or stronger as high, which carries a higher risk of retinal problems (EyeWiki, AAO). A cylinder of 1.50 is where the AAO says astigmatism typically needs correction.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">Can you get an online eye prescription?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>Not from a reader like this: it explains a prescription but cannot create one. The AAO says online vision tests can measure prescription power for healthy adults aged 18 to 39 with mild to moderate prescriptions and no symptoms, but cannot detect eye disease with hidden symptoms, suit neither high-power nor irregular prescriptions, and must never be used to order contact lenses. Prescriptions must be approved by an optometrist or ophthalmologist. In the UK, eligible people can have a free NHS sight test every two years. To convert 6\/6 or 20\/20, use our <a href=\"https:\/\/laseristanbulclinic.com\/en\/eye-tools\/visual-acuity-converter\/\">visual acuity converter<\/a>.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"qa-row\" data-reveal><div class=\"row\"><h3 class=\"qa-q col-12 col-lg-4\">Which prescriptions can laser or lens surgery treat?<\/h3><div class=\"qa-a prose col-12 col-lg-8\"><p data-reveal>The Royal College of Ophthalmologists (RCOphth) says laser suits people over 18 whose prescription has changed by no more than 0.5 D in two years and falls within these ranges; higher ones usually need a lens-based option.<\/p><div class=\"tbl-wrap\" data-reveal><table class=\"tbl rsp\"><thead><tr><th scope=\"col\">Correction<\/th><th scope=\"col\">Typical range<\/th><\/tr><\/thead><tbody><tr><th scope=\"row\">Laser: short sight<\/th><td data-label=\"Typical range\">Up to \u221210.00 D<\/td><\/tr><tr><th scope=\"row\">Laser: long sight<\/th><td data-label=\"Typical range\">Up to +4.00 D<\/td><\/tr><tr><th scope=\"row\">Laser: astigmatism<\/th><td data-label=\"Typical range\">Up to \u00b16.00 D<\/td><\/tr><tr><th scope=\"row\">ICL (FDA range): myopia \/ toric cylinder<\/th><td data-label=\"Typical range\">\u22123.00 to \u221220.00 D \/ 1.00 to 4.00 D<\/td><\/tr><\/tbody><\/table><\/div><p data-reveal>Read about <a href=\"https:\/\/laseristanbulclinic.com\/en\/myopia-treatment\/\">myopia (short-sightedness) treatment<\/a> or <a href=\"https:\/\/laseristanbulclinic.com\/en\/laser-eye-surgery-turkey\/\">laser eye surgery in Turkey<\/a>. Your surgeon decides after scans of your cornea, lens and retina.<\/p><\/div><\/div><\/div>\n\t\t\t<\/div>\n\t<\/div><\/div><\/div><\/section>\n<!-- FAQ (Question and answer rows) End -->\n\n\n<!-- Note (Callout) Start -->\n<section class=\"psec pad tight\" id=\"disclaimer\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\">\n\t\t\t<div class=\"callout line\" data-reveal><p data-reveal>This reader explains the numbers on a glasses prescription. It does not measure your eyes, diagnose any condition or show whether you are suitable for treatment. Only an optometrist or ophthalmologist can examine you and prescribe. If your vision changes suddenly, see an eye doctor.<\/p><\/div>\n\t<\/div><\/div><\/div><\/section>\n<!-- Note (Callout) End -->\n\n\n<!-- Call to Action (Panel) Start -->\n<section class=\"panel grad cta-panel\" id=\"try-our-other-free-eye-tools\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\"><div class=\"cta-panel-inner row\">\n\t<div class=\"col-12\"><div class=\"cta-panel-copy\">\n\t\t\t\t<h2 class=\"t48\" data-reveal>Try our other free eye tools<\/h2>\n\t\t\t\t<p class=\"t22\" data-reveal>Take the <a href=\"\/en\/eye-tools\/astigmatism-test\/\">astigmatism test<\/a>, the <a href=\"\/en\/eye-tools\/lens-finder-quiz\/\">lens finder quiz<\/a>, the <a href=\"\/en\/eye-tools\/colour-blindness-test\/\">colour blindness test<\/a> or the <a href=\"\/en\/eye-tools\/amsler-grid-test\/\">Amsler grid test<\/a>, or explore the <a href=\"\/en\/eye-tools\/eye-colour-calculator\/\">eye colour chart and inheritance calculator<\/a>.<\/p><p class=\"t22\" data-reveal>Prof. Dr. Ahmet Sat\u0131c\u0131 (laser, ICL and lens exchange) and Op. Dr. Aysan Bayram (laser) treat short sight, long sight and astigmatism in a fully equipped, Ministry of Health\u2013licensed operating theatre in Istanbul.<\/p>\t\t\t<\/div><\/div>\n\t<div class=\"col-12\"><div class=\"cta-panel-side\"><\/div><\/div>\n<\/div><\/div><\/div><\/div><\/section>\n<!-- Call to Action (Panel) End -->\n\n\n<!-- FAQ (FAQ accordion) Start -->\n<section class=\"faq pad\" id=\"faq\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\"><div class=\"faq-grid\">\n\t<div class=\"faq-side\">\n\t\t\t\t<h2 class=\"t48\" data-reveal>Eye prescription: frequently asked questions<\/h2>\n\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"acc\" data-stagger>\n\t\t\t\t<div class=\"acc-item is-open\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"true\" aria-controls=\"faq-00201a7a-a1\" id=\"faq-00201a7a-q1\">What does SPH mean on an eye prescription?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a1\" role=\"region\" aria-labelledby=\"faq-00201a7a-q1\"><div class=\"acc-body\"><p data-reveal>SPH is the sphere, the main lens power in dioptres. Minus corrects short sight; plus corrects long sight.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"acc-item\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"false\" aria-controls=\"faq-00201a7a-a2\" id=\"faq-00201a7a-q2\">What does CYL mean on an eye prescription?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a2\" role=\"region\" aria-labelledby=\"faq-00201a7a-q2\"><div class=\"acc-body\"><p data-reveal>CYL is the cylinder, the extra power that corrects astigmatism. It always comes with an axis.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"acc-item\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"false\" aria-controls=\"faq-00201a7a-a3\" id=\"faq-00201a7a-q3\">What is the axis on an eye prescription?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a3\" role=\"region\" aria-labelledby=\"faq-00201a7a-q3\"><div class=\"acc-body\"><p data-reveal>The axis, from 1 to 180 degrees, is the direction of the astigmatism. It is only used with a cylinder.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"acc-item\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"false\" aria-controls=\"faq-00201a7a-a4\" id=\"faq-00201a7a-q4\">What does BVD mean on an eye prescription?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a4\" role=\"region\" aria-labelledby=\"faq-00201a7a-q4\"><div class=\"acc-body\"><p data-reveal>BVD is back vertex distance, the gap between lens and eye, normally 12 to 14 mm. It matters mostly above about \u00b14.00 D.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"acc-item\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"false\" aria-controls=\"faq-00201a7a-a5\" id=\"faq-00201a7a-q5\">Can I use my glasses prescription to order contact lenses?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a5\" role=\"region\" aria-labelledby=\"faq-00201a7a-q5\"><div class=\"acc-body\"><p data-reveal>No. A contact-lens prescription is different because the lens sits on the eye, and the AAO says never to order contacts from a home vision test.<\/p><\/div><\/div><\/div>\n\t\t\t\t<div class=\"acc-item\"><h3><button type=\"button\" class=\"t32\" aria-expanded=\"false\" aria-controls=\"faq-00201a7a-a6\" id=\"faq-00201a7a-q6\">Does my prescription show whether I can have laser eye surgery?<svg width=\"24\" height=\"24\" aria-hidden=\"true\"><use href=\"#i-plus\"\/><\/svg><\/button><\/h3><div class=\"acc-panel\" id=\"faq-00201a7a-a6\" role=\"region\" aria-labelledby=\"faq-00201a7a-q6\"><div class=\"acc-body\"><p data-reveal>It gives a first indication: the RCOphth says laser most likely suits up to \u221210.00 D, +4.00 D and \u00b16.00 D of astigmatism. Your surgeon must also check your corneas and eye health.<\/p><\/div><\/div><\/div>\n\t\t\t<\/div>\n\t<\/div><\/div><\/div><\/div><script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"What does SPH mean on an eye prescription?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"SPH is the sphere, the main lens power in dioptres. Minus corrects short sight; plus corrects long sight.\"}},{\"@type\":\"Question\",\"name\":\"What does CYL mean on an eye prescription?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"CYL is the cylinder, the extra power that corrects astigmatism. It always comes with an axis.\"}},{\"@type\":\"Question\",\"name\":\"What is the axis on an eye prescription?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The axis, from 1 to 180 degrees, is the direction of the astigmatism. It is only used with a cylinder.\"}},{\"@type\":\"Question\",\"name\":\"What does BVD mean on an eye prescription?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"BVD is back vertex distance, the gap between lens and eye, normally 12 to 14 mm. It matters mostly above about \u00b14.00 D.\"}},{\"@type\":\"Question\",\"name\":\"Can I use my glasses prescription to order contact lenses?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. A contact-lens prescription is different because the lens sits on the eye, and the AAO says never to order contacts from a home vision test.\"}},{\"@type\":\"Question\",\"name\":\"Does my prescription show whether I can have laser eye surgery?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It gives a first indication: the RCOphth says laser most likely suits up to \u221210.00 D, +4.00 D and \u00b16.00 D of astigmatism. Your surgeon must also check your corneas and eye health.\"}}]}<\/script><\/section>\n<!-- FAQ (FAQ accordion) End -->\n\n\n<!-- List (Sources and medical review) Start -->\n<section class=\"psec pad tight\"><div class=\"container-fluid px-0\"><div class=\"row g-0\"><div class=\"col-12\"><details class=\"sources\" data-reveal><summary class=\"t22\">Sources for the facts on this page<\/summary><ol>\n\t\t<li>OD\/OS, sphere (minus = short-sighted, plus = long-sighted, &#8220;\u22129.00 D&#8221; example), cylinder, axis (1\u2013180), add, prism (double vision), contact-lens prescription differs from glasses: American Academy of Ophthalmology, &#8220;How to Read Your Eyeglasses Prescription&#8221; https:\/\/www.aao.org\/eye-health\/glasses-contacts\/how-to-read-eyeglasses-prescription<\/li>\n\t\t<li>Astigmatism: most people have 0.5\u20130.75 D, 1.5 D or more typically needs correction; can change over time: AAO, &#8220;What Is Astigmatism?&#8221; https:\/\/www.aao.org\/eye-health\/diseases\/what-is-astigmatism<\/li>\n\t\t<li>Astigmatism = &#8220;rugby ball&#8221; shape, light focused at more than one place; short-sightedness and long-sightedness definitions; laser and lens surgery not available on the NHS: NHS, &#8220;Astigmatism&#8221; https:\/\/www.nhs.uk\/conditions\/astigmatism\/ \u00b7 &#8220;Short-sightedness (myopia)&#8221; https:\/\/www.nhs.uk\/conditions\/short-sightedness\/ \u00b7 &#8220;Long-sightedness (hyperopia)&#8221; https:\/\/www.nhs.uk\/conditions\/long-sightedness\/<\/li>\n\t\t<li>Presbyopia becomes noticeable shortly after age 40: AAO, &#8220;What Is Presbyopia?&#8221; https:\/\/www.aao.org\/eye-health\/diseases\/what-is-presbyopia<\/li>\n\t\t<li>Online vision tests: healthy adults 18\u201339, mild to moderate prescriptions; cannot detect hidden disease; not for high-power or irregular prescriptions; never for contacts; prescriptions approved by an optometrist or ophthalmologist; exams every 5\u201310 years at 18\u201339: AAO, &#8220;Using a home vision test to order glasses online&#8221; https:\/\/www.aao.org\/eye-health\/tips-prevention\/self-home-vision-test-order-glasses-online<\/li>\n\t\t<li>Keeping spherical equivalent constant when changing cylinder (+0.50 D cylinder with \u22120.25 D sphere); axis scale 1\u2013180: AAO, &#8220;Refraction 101: Go Forth and Refract&#8221; https:\/\/www.aao.org\/young-ophthalmologists\/yo-info\/article\/refraction-101-go-forth-and-refract<\/li>\n\t\t<li>Myopia \u2264 \u22120.50 D spherical equivalent; low myopia down to just above \u22126.00 D; high myopia \u2264 \u22126.00 D; spherical-equivalent definition: Flitcroft DI, et al., &#8220;IMI \u2013 Defining and Classifying Myopia&#8221;, Invest Ophthalmol Vis Sci 2019;60:M20\u2013M30 https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC6735818<\/li>\n\t\t<li>High myopia \u2265 \u22126.00 D; complications (retinal detachment, myopic maculopathy, macular holes); yearly review when stable: EyeWiki (AAO), &#8220;Pathologic Myopia (Myopic Degeneration)&#8221; https:\/\/eyewiki.org\/Pathologic_Myopia_(Myopic_Degeneration)<\/li>\n\t\t<li>With-the-rule (steepest vertical, axis about 90 in plus-cylinder terms) and against-the-rule (steepest horizontal, about 180; most common in adults over 40): EyeWiki (AAO), &#8220;Physiology of Astigmatism&#8221; https:\/\/eyewiki.org\/Physiology_of_Astigmatism<\/li>\n\t\t<li>Anisometropia (\u2265 1.0 D difference between eyes) in 17.9% of 134,603 refractive-surgery candidates: Deuchert et al., PLoS One 2025 https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC11698341\/<\/li>\n\t\t<li>EVO ICL FDA range: myopia \u22123.0 to \u221220.0 D; toric cylinder 1.0\u20134.0 D: EyeWiki (AAO), &#8220;Implantable Collamer Lens&#8221; https:\/\/eyewiki.org\/Implantable_Collamer_Lens<\/li>\n\t\t<li>Spectacle prescriptions normally treated as current for two years: College of Optometrists, &#8220;Prescriptions more than two years old&#8221; https:\/\/www.college-optometrists.org\/clinical-guidance\/guidance\/knowledge,-skills-and-performance\/sale-and-supply-of-spectacles\/prescriptions-more-than-two-years-old<\/li>\n\t\t<li>Free NHS sight test every 2 years for eligible people: NHS, &#8220;How often can I have a free NHS eye test?&#8221; https:\/\/www.nhs.uk\/nhs-services\/opticians\/how-often-can-i-have-a-free-nhs-eye-test\/ (carried from the Online eye test page, where it was checked)<\/li>\n\t\t<li>Dioptre = reciprocal metre, 3 D focuses at one-third of a metre, 0.25 D steps; OU\/RE\/LE\/plano\/DS\/ADD\/PD definitions; transposition rule (flip cylinder sign, add 90\u00b0 to axis, subtract 180\u00b0 if over 180); back vertex distance (12\u201314 mm, significant beyond \u00b14.00 D): Wikipedia, &#8220;Dioptre&#8221; https:\/\/en.wikipedia.org\/wiki\/Dioptre \u00b7 &#8220;Eyeglass prescription&#8221; https:\/\/en.wikipedia.org\/wiki\/Eyeglass_prescription \u00b7 &#8220;Vertex distance&#8221; https:\/\/en.wikipedia.org\/wiki\/Vertex_distance (reference summaries; the reviewing surgeon may confirm against a textbook)<\/li>\n\t\t<li>Emergency numbers: 112 in the EU, European Commission https:\/\/digital-strategy.ec.europa.eu\/en\/policies\/112 \u00b7 112 in T\u00fcrkiye, 112.gov.tr https:\/\/www.112.gov.tr\/kilis\/acil-durumlarda-tek-numara-112 \u00b7 999 in the UK, NHS https:\/\/www.nhs.uk\/nhs-services\/urgent-and-emergency-care-services\/when-to-call-999\/ \u00b7 911 in Canada, Parks Canada https:\/\/parks.canada.ca\/voyage-travel\/securite-safety\/urgence-emergency<\/li>\n\t\t<li>Own calculations (not external facts): spherical equivalent (sphere + cylinder \u00f7 2), transposition examples, near power (sphere + ADD), the &#8220;mixed astigmatism&#8221; test (sphere and sphere + cylinder of opposite signs), the 61\u2013120\u00b0 \/ 1\u201330\u00b0 \/ 151\u2013180\u00b0 orientation boundaries (to be confirmed by the reviewing surgeon), and the five QA samples.<\/li>\n\t<\/ol><\/details><\/div><\/div><\/div><\/section>\n<!-- List (Sources and medical review) End -->\n\n\n<!-- Call to Action (Assessment band) Start -->\n<section class=\"cta-band\" id=\"assessment\">\n\t<div class=\"contact-bg\" aria-hidden=\"true\"><span><\/span><span><\/span><span><\/span><\/div>\n\t<div class=\"cta-inner pad container-fluid\"><div class=\"row\">\n\t\t<div class=\"col-12 col-lg-7\"><div class=\"cta-copy\">\n\t\t\t\t\t\t<h2 class=\"t64\" data-reveal>Want to know what your prescription means for treatment?<\/h2>\n\t\t\t\t\t\t<p class=\"t22\" data-reveal>Send us your prescription and one of our surgeons will tell you which treatments may suit you, with no obligation.<\/p>\t\t\t\t\t\t<div class=\"cta-actions\" data-reveal><a class=\"pill pill-white\" href=\"#tool\"><span class=\"pill-dot\" aria-hidden=\"true\"><\/span><span class=\"pill-label\">Send my prescription for a free review<\/span><\/a><a class=\"pill pill-line\" href=\"https:\/\/wa.me\/905416390785?text=Hello%20Laser%20Istanbul%20Clinic%2C%20I%20would%20like%20some%20information%20about%20eye%20treatment.%20Sent%20from%3A%20https%3A%2F%2Flaseristanbulclinic.com%2Fen%2F\" target=\"_blank\" rel=\"noopener\"><span class=\"pill-dot\" aria-hidden=\"true\"><\/span><span class=\"pill-label\">WhatsApp: +90 541 639 07 85<\/span><\/a><\/div>\n\t\t\t\t\t<\/div><\/div>\n\t\t\t\t<div class=\"col-12 col-lg-5\"><div class=\"proof-card\" data-reveal>\n\t\t\t\t\t\t<div class=\"proof-text\">\n\t\t\t\t\t\t\t\t<h3 class=\"t48\">3 eye surgeons<\/h3>\n\t\t\t\t\t\t\t\t\t\t\t\t<p class=\"t22\">Your case is reviewed by a named surgeon, not a salesperson. 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