Understanding Your Eye Exam Results: Common Terms Explained
October 15, 2026
Quick Answer:
Eye exam results use shorthand to describe your prescription. SPH (sphere) indicates nearsightedness or farsightedness, CYL (cylinder) and AXIS describe astigmatism, ADD is the extra power for reading in multifocal lenses, and PD (pupillary distance) is the spacing between your pupils. Knowing these terms helps you understand your results and shop for glasses or contacts confidently.
Your eye exam report may look like a chart of numbers and abbreviations. Here’s what the most common terms mean.
Prescription terms
- OD and OS. OD refers to the right eye (oculus dexter), and OS refers to the left eye (oculus sinister). OU means both eyes.
- SPH (Sphere). The main lens power. A minus (−) number means nearsightedness, which makes distant objects blurry. A plus (+) number means farsightedness, which makes close objects harder to see.
- CYL (Cylinder). The added power to correct astigmatism, an irregular curvature of the eye that blurs vision at all distances.
- AXIS. The orientation, in degrees from 1 to 180, of the astigmatism correction. It only appears when CYL is present.
- ADD. The extra magnifying power for reading or near tasks, used in multifocal and reading lenses. It typically appears in age-related near vision changes, called presbyopia.
- PD (Pupillary Distance). The distance between your pupils in millimeters. It helps position lenses correctly in your frames. Some reports list monocular PDs for each eye.
- Prism. Included when the eyes need help aligning. Not everyone needs prism correction.
Vision terms
- 20/20 vision. A standard measure meaning you can see at 20 feet what a person with typical vision sees at 20 feet. 20/40 means you need to be 20 feet away to see what most people can see at 40 feet.
Eye health terms
- IOP (Intraocular Pressure). Fluid pressure inside the eye. Measurements typically fall between about 10 and 21 mmHg, but pressure alone doesn’t determine glaucoma risk.
- Cup-to-disc ratio. A measurement of the optic nerve’s appearance. Changes in this ratio over time can be an early sign of glaucoma and are monitored at follow-up visits.
- Dilated fundus exam. A detailed view of the retina, macula, optic nerve, and blood vessels after drops widen the pupils.
Questions to ask at your visit
- What does my prescription mean for everyday tasks?
- Do my results show any changes since my last exam?
- Is there anything I should monitor or return sooner for?
- Which lens options and coatings would suit my lifestyle?
Frequently Asked Questions
Can I use my prescription from another doctor?
Yes, you’re entitled to a copy of your prescription. Bring it with you when shopping for glasses or contacts.
Why does my prescription change over time?
Eye focusing ability naturally changes with age, and conditions like diabetes can also affect vision. Regular exams track these changes.
What’s the difference between a prescription for glasses and one for contacts?
Contact lens prescriptions include lens-specific measurements, such as base curve and diameter, and require a separate fitting. The two prescriptions are not interchangeable.
Have questions about your results?
Call (978) 774-7033 or ask us at your next visit. You can also review our exam services .
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