How to read your eye prescription.

OD (oculus dexter) is the right eye; OS (oculus sinister) is the left eye. OU (oculus uterque) means both eyes together. On most prescriptions OD is listed first, in the top row. The abbreviations come from Latin and appear on paper forms and lens orders worldwide.

SPH (sphere) is the main correction, in diopters, for nearsightedness (minus) or farsightedness (plus). CYL (cylinder) corrects astigmatism, an uneven curve in the eye. AXIS (0 to 180 degrees) states the orientation of that curve. CYL and AXIS always appear together; one without the other means the paper is incomplete.

A minus number means the eye is nearsighted: light from distant objects focuses in front of the retina instead of on it, so far things blur while close things stay sharp. A plus number means the opposite, with light focusing behind the retina.

−3.00 D sits in the moderate range on the standard scale (mild is 0 to −3.00, moderate −3.00 to −6.00, high beyond that). It is a common, unremarkable correction, not a severe one. The number describes how much lens power is needed, not a judgment on the eye.

ADD is extra plus power for close-up focusing, added to the distance number for reading, screens, or other near work. It typically increases with age and applies to both eyes almost equally. It appears in progressive and bifocal lenses, or as a separate pair of reading glasses.

Yes. PD (pupillary distance) is the space between your pupils in millimeters, and online lens shops require it to center the lenses correctly in the frame. Opticians often leave it off a printed prescription because in-store measurement handles it directly. It can be measured at home with a phone camera.

Validity is set by law in your country, commonly one to two years, and shops enforce it by rejecting expired orders. The date is on the paper itself. If your paper does not show a date or the date has passed, a new eye exam is required before ordering.

Not directly. Glasses and contact lens numbers differ because contacts sit on the eye while glasses sit a few millimeters in front of it (vertex distance), which matters most above about ±4.00 D. Contact lenses also need a base curve and diameter that a glasses paper does not include.

A short adjustment period, often the first few days, is a common report when a correction changes, especially with new astigmatism or PD numbers. If headaches persist beyond a week or two, the fitting or the numbers may be off, and the shop or optician is who to contact.