Reading Your Prescription

Understanding Your Prescription

How do I read my prescription?

Your prescription is divided under OD and OS—Latin abbreviations for Ocular Dexter (right eye) and Ocular Sinister (left eye).

• Sphere (SPH): The first number, showing correction for nearsightedness (minus sign) or farsightedness (plus sign). It will have a plus (+) or minus (-) sign, or "PL" for Plano (zero/no correction needed).

  • Common range: -10.00 to +6.00

  • Higher absolute numbers = stronger correction needed

• Cylinder (CYL) & Axis: For astigmatism correction, which addresses irregular cornea curvature. These always appear together—you either have both or neither.

  • Cylinder range: typically -4.00 to +4.00

  • Axis range: 1 to 180 degrees (indicates orientation of astigmatism)

  • Note: Some doctors write cylinder in minus form, others in plus—we can work with either

• Add (Addition): Indicates extra magnification needed for reading (aging-related presbyopia, typically 40+). This number is always positive (+0.75 to +3.00) and requires bifocal/progressive lenses or two separate pairs.

  • Tip: Higher Add numbers mean stronger reading correction

Prescription validity: Most prescriptions are valid for 1-2 years. Check the expiration date before ordering.

If I don't have my prescription, can you get it from my doctor?

Doctors aren't required to provide prescriptions to us, but under federal law (Fairness to Contact Lens Consumers Act and similar eyeglass regulations), they must release it to you immediately after your eye exam—even if you don't ask. Request a copy directly from your doctor.

Pro tip: Take a clear photo of your prescription right away for your records.

What does "Sphere" or "DS" mean in the Cylinder field?

"DS" stands for "Diopters Sphere"—it means you need no cylinder or axis correction (no astigmatism). Enter "None" for these fields when ordering.

What if my prescription shows different formats or abbreviations?

Common variations you might see:

• OU (Oculus Uterque): Both eyes together

• Balance or BAL: Non-prescription lens to match the other eye

• Prism & Base: Special correction for eye alignment issues (contact us for assistance)

• NVO (Near Vision Only): Prescription for reading glasses only

Pupil Distance (PD)

What is PD?

Pupil Distance is the distance between the centers of your pupils, measured in millimeters. It ensures lenses are properly centered in your frames for optimal vision and comfort.

Why it matters: Incorrect PD can cause eye strain, headaches, blurred vision, and difficulty focusing—even with the correct prescription.

How do I get my PD?

• Ask your eye doctor or local optician (takes just a couple minutes—it's often free)

• Use our Online Pupil Meter to measure yourself

• Use a standard ruler and mirror (measure from the center of one pupil to the other)

• Have a friend help you measure for greater accuracy

Average adult PD: 54-74mm | Average women: 62mm | Average men: 64mm

Which PD number(s) should I enter?

For Single Vision (Distance or Reading) Lenses:

• Distance/Near format (55-75mm): Use the first number for distance; second for reading

  • Distance PD is typically 2-3mm wider than near PD

• Right/Left Eye format (27.5-37.5mm each): Add both numbers together for Distance PD

  • Example: R 31.5 + L 32.5 = 64mm total

• Single digit R/L format: Double the number for Distance PD

  • Example: "32/32" means 32+32 = 64mm

For Progressive/Bifocal Lenses:

• Distance/Near format (55-75mm): Enter both the Distance and Near values

  • Near PD is critical for progressives to ensure proper reading zone alignment

• Right/Left Eye format (27.5-37.5mm each): Add together for Far PD

• Single digit R/L format: Double the numbers for Far PD

Pro tip: For progressives and bifocals, providing separate right/left PD measurements (if available) gives the most precise results.

Does PD change over time?

PD remains constant in adults after full facial development (typically after age 18-20). Children should be remeasured with each new prescription as their faces grow.

Does PD affect frame size?

No. PD only ensures lenses are properly centered in whatever frame you choose. However, selecting frames appropriate for your face size helps ensure your PD falls comfortably within the lens area.

Guideline: For very narrow or wide PDs, avoid extremely oversized or undersized frames.