How to Read an Eye Prescription - Every Number, Letter and Symbol Explained (2026)

How to Read an Eye Prescription - You just had an eye test, and the optician hands you a small piece of paper covered in abbreviations, plus and minus signs, and numbers that mean nothing to you. You nod politely and walk out, unsure what it all means. Sound familiar? I’ve done that exact thing myself; for years, I collected eye prescriptions without truly understanding them. Then I finally sat down and learned what every number meant, and to my surprise, it only took about 20 minutes. Now I can glance at my prescription and immediately understand my vision.

This guide breaks down every part of a standard pair of glasses’ prescription in plain English. No jargon. No guessing. By the end, you will know exactly what your optician wrote and why.

complete eye health guide: vision care, prevention and wellness

 

WHAT YOU WILL UNDERSTAND AFTER READING THIS

What OD and OS mean — and why they matter What sphere (SPH) tells you about your vision What does cylinder (CYL) and axis mean for astigmatism What ADD means and when it appears on your prescription What PD is and why it is critical for making your glasses How to tell if you are short-sighted or long-sighted from your numbers What NV, DV, and prism notations mean How to compare prescriptions over time to track your vision changes

 

What Does a typical eye prescription look like?

Here is a sample prescription. We will use it throughout this guide to explain each part.

 

	SPH	CYL	AXIS	ADD	PD
OD (Right Eye)	-2.50	-0.75	180	+2.00	32
OS (Left Eye)	-1.75	-1.25	165	+2.00	31

 

Every eye prescription follows this basic structure. The columns may appear in slightly different order on different forms. But the same abbreviations always appear. Let us go through each one.

OD and OS - Which Eye Is Which?

These two abbreviations come from Latin. They tell you which eye each row of numbers applies to.

 

Abbreviation	Latin Origin	Meaning
OD	Oculus Dexter	Right eye
OS	Oculus Sinister	Left eye
OU	Oculus Uterque	Both eyes (used when the same value applies to both)

Your right eye is always listed first. If you are ever unsure which row is which, look for OD at the top. I found this confusing at first because the right eye on the paper feels like the left when you are looking at it. Just remember: OD = right, always.

SPH (Sphere) - The Most Important Number on Your Prescription

The sphere number tells you the main lens power you need. It corrects short-sightedness or long-sightedness. This is the single most important number for most people.

how screen use and myopia are connected

 

SPH Number	What It Means	Your Vision Issue
Negative (e.g. -2.50)	You are short-sighted (myopic)	Distant objects are blurry
Positive (e.g. +1.75)	You are long-sighted (hyperopic)	Close objects are blurry
0.00 or plano	No correction needed for this eye	Normal distance vision
Higher number (e.g. -6.00)	Stronger prescription needed	Significant refractive error
Lower number (e.g. -0.50)	Mild correction needed	Minor refractive error

The minus sign means short-sighted. The plus sign means long-sighted. The higher the number — whether plus or minus — the stronger the lens you need.

In the sample prescription above, both eyes have negative sphere values. That person is short-sighted. Their right eye needs a -2.50 correction. Their left needs -1.75. The right eye has slightly worse distance vision.

CYL (Cylinder) and Axis - What Astigmatism Looks Like on Paper

Not everyone has CYL value. If this column is blank or marked with a dash, you do not have astigmatism in that eye.

Astigmatism means your cornea — the front of your eye — is not perfectly round. It is slightly oval or rugby-ball shaped. This leads to blurred or distorted vision at every distance. CYL and Axis together correct this.

 

Term	What It Measures	What the Number Tells You
CYL (Cylinder)	The power of lens needed to correct astigmatism	Negative = most common form. Higher number = stronger astigmatism
AXIS	The angle of astigmatism in degrees	A number between 1 and 180. Tells the lab where to position the corrective power in the lens

You cannot have an Axis without a CYL. They always come as a pair. The Axis alone means nothing — it just positions the CYL correction at the right angle for your eye.

In our sample, the right eye has CYL -0.75 at Axis 180. That means there is mild astigmatism with the correction placed horizontally. The left eye has stronger astigmatism (-1.25) at a slightly different angle (165).

ADD - What It Means and When It Appears

ADD stands for Addition power. It only appears on prescriptions for people who need reading glasses or progressive lenses. If you are under 40 and your ADD column is blank, that is completely normal.

After age 40, the lens inside your eye starts to lose flexibility. Reading small print becomes harder. This is called presbyopia. It happens to almost everyone. The ADD value is the extra magnifying power added to the lower part of your lens to help you read.

eye health after 40 and vision changes to expect

 

ADD Value	What It Suggests	Typical Age
+0.75 to +1.25	Mild presbyopia — early reading difficulty	40 to 45
+1.50 to +2.00	Moderate presbyopia	45 to 55
+2.25 to +2.50	Significant presbyopia	55 to 65
+2.75 to +3.00	Advanced presbyopia	65 and over

In our sample prescription, both eyes have ADD +2.00. That person is likely in their 50s and uses either bifocal or progressive lenses. Reading glasses alone would also carry this power.

PD (Pupillary Distance) - The Number People Often Forget to Ask For

Pupillary distance (PD) is the measurement in millimetres between the centers of your two pupils. It is critical for making glasses. “Without it, each lens’s optical center can’t be properly aligned with your eyes

In our sample, the right eye PD is 32mm, and the left is 31mm. Added together gives a total PD of 63mm. Some prescriptions give a single total PD number instead of splitting it by eye.

 

IMPORTANT NOTE FOR Adel'S READERS

[Many opticians do not include PD on the written prescription unless asked. You have a legal right to your full prescription, including PD, in most countries. Always ask for it. You will need it if you ever order glasses online. This is a genuinely useful tip that most articles do not make clear enough.]

Other Abbreviations You Might See on Your Prescription

Abbreviation	Full Name	What It Means
DV	Distance Vision	The correction for seeing far away — used on bifocal prescriptions
NV	Near Vision	The correction for reading — the ADD applied to the base prescription
Int or INT	Intermediate	Mid-distance correction — for computer distance use
Prism	Prism	Corrects eye alignment problems (strabismus). Rare. Measured in prism dioptres
Base	Base direction	Used with prism — tells the lab which direction the prism points
VA	Visual Acuity	How well you can see — written as 6/6 (perfect) or 6/12 (reduced)
BAL	Balance	Used when one eye is not correctable — the other lens is balanced for comfort
Plano or PL	Plano	Zero power — no correction needed for that measurement

How Strong Is Your Prescription? Understanding the Scale

People often ask whether their prescription is weak or strong. Here is a simple guide.

 

Prescription Strength	SPH Range	What This Means in Daily Life
Mild	0.25 to 1.50	Blurry only in certain conditions. Many people manage without glasses
Moderate	1.75 to 3.00	Regular glasses or contacts needed for clear vision
Strong	3.25 to 5.00	Noticeably limited without correction. Thinner lens options recommended
Very Strong	5.25 to 9.00	Significant dependence on glasses. High-index lenses worth considering
Extreme	Over 9.00	Specialist lens consultation recommended. May explore refractive surgery options

How to Compare Two Prescriptions Over Time

Your vision can change year on year. Comparing prescriptions helps you track whether things are stable, improving, or getting worse.

• Look at the sphere change — if it has increased by 0.50 or more since last year, your prescription has changed meaningfully.
• Check both eyes separately — it is common for one eye to change while the other stays the same.
• Watch the CYL number — increasing CYL means astigmatism is progressing. This is common in younger adults and in people with myopia.
• Track the ADD number — if your ADD keeps increasing every year, this is normal presbyopia progression.
• Compare the PD—this should not change significantly in adulthood. If it does, ask your optician why.

Is a contact lens prescription identical to a glasses prescription?

No. This surprises many people. A contact lens prescription and a glasses prescription are different documents. Do not try to use one for the other.

Glasses sit about 12mm in front of your eye. Contacts sit directly on the cornea. This difference in distance changes the effective power required. A glasses prescription must be converted to account for this difference — this is done during a contact lens fitting appointment.

 

Feature	Glasses Prescription	Contact Lens Prescription
Power (SPH/CYL)	Calculated for 12mm from eye	Adjusted for on-eye position
Includes BC (Base Curve)	No	Yes — determines lens curvature to fit your cornea
Includes DIA (Diameter)	No	Yes — the physical size of the lens
Includes brand	No	Yes — specific to lens type tested during fitting
Expiry	Usually, 2 years	Usually 1 year (requires annual fitting check)

I learned this the hard way when I tried to order contacts using my glasses prescription. The optician explained that the numbers need adjusting. Always ask for a separate contact lens prescription if you want to wear contacts.

My Personal Experience Reading My Prescription

ADEL GALAL

I wore glasses for years without ever properly understanding my prescription. It felt like it was deliberately written to be confusing. When I finally sat down and decoded it, I found I was moderately short-sighted Both eyes measure around -2.50 sphere, with mild astigmatism present.. The ADD value appeared for the first time at age 47. That was a memorable day. The most useful thing I did was photograph every prescription over the years. Now I can track exactly how my vision has changed decade by decade. My right eye has been stable for 5 years. My left eye still drifts slightly. I also always ask for my PD now. Every single time. I had to order glasses in a hurry once and could not get it without the PD. Never again. Understanding your prescription puts you in control. You can have an informed conversation with your optician. You can spot errors in the glasses you receive. You can make sensible decisions about lens type and frame choice.

Key Takeaways - How to Read an Eye Prescription

 

SUMMARY

OD = right eye. OS = left eye. Always in that order on your prescription SPH (sphere) is the main correction. Minus = short-sighted. Plus = long-sighted CYL and Axis correct astigmatism. They always appear together ADD is the reading boost for presbyopia. Appears from around age 40 onwards PD is your pupillary distance. Always ask for it. You are entitled to it Contact lens prescriptions differ from glasses prescriptions. Never use one for the other Track your prescriptions over time to understand how your vision changes A higher sphere number (plus or minus) means a stronger correction is needed

References and Sources

1- Understanding Your Eye Prescription — American Academy of Ophthalmology

https://www.aao.org/eye-health/glasses-contacts/understanding-eyeglass-prescription

AAO authority. Use for: prescription abbreviations, OD/OS, SPH/CYL/ADD definitions.

2- Refractive Errors — National Eye Institute (NIH)

https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/refractive-errors

NIH authority. Use for: myopia, hyperopia, astigmatism, and presbyopia definitions and prevalence.

3- Presbyopia — American Optometric Association

https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/presbyopia

Professional optometry body. Use for: ADD power, presbyopia age of onset, and reading addition values.

4- Contact Lens Prescriptions — FDA

https://www.fda.gov/medical-devices/contact-lenses/contact-lens-prescriptions

US FDA regulatory authority. Use for: contact vs glasses prescription differences and patient rights.

5- Astigmatism — American Academy of Ophthalmology

https://www.aao.org/eye-health/diseases/what-is-astigmatism

AAO clinical authority. Use for: astigmatism mechanism, CYL/Axis explanation, and treatment options.