A glasses prescription may have terms on it that you don't understand. Let's go through some of them. • OD/OS/OU - These are abbreviations for oculus dextrus, oculus sinister, and oculus uterque. They are Latin terms for right eye, left eye, and both eyes. A lot of modern optometrists use RE and LE nowadays (right eye and left eye). • SPH - This is short for 'sphere'. It refers to the power of your eye's lens, which optometrists measure in 'dioptres' (D). If the number in this section features a minus symbol (-), you're shortsighted. If it has a plus symbol (+) or no symbol, you are long-sighted. • CYL - This is short for 'cylinder'. Cylinder indicates lens power for astigmatism. A number in this column will usually have a minus sign in front of it, but you may sometimes find a plus sign. If there is no number at all, you either have no astigmatism, or it's very slight and you have nothing to worry about. • Axis - This will be a number between 1 and 180. You will only find an axis when your prescription also has a cylinder power. An 'x' always precedes the axis. • Add - This is the power that helps you read. It is always a positive number, even if it doesn't start with a plus sign (+). It is usually between 0.75 and 3.00. It will be the same for both eyes. • Prism - Optometrists measure this in prism dioptres, or 'p.d.' They may also use a ⧍ symbol. Few prescriptions feature a prism measurement. This is to help with eye alignment problems. An abbreviation will follow the p.d. measurement - BU/BD/BI/BO. These mean base up, base down, base in, and base out. This is the direction that the thickest edge of the lens will move in adjustment. Your prescription may also feature specific lens recommendations. This could include anti-reflective coating, photochromic (see above), or progressive lenses. These are all considerations designed to give you a comfortable corrective experience.