Prescription lenses are customized according to the results of an eye examination. They are used to correct vision conditions such as myopia, hyperopia, astigmatism, and presbyopia.
Your prescription should be issued by a qualified optometrist, ophthalmologist, or other licensed eye care professional. This guide explains the most common prescription terms—including SPH, CYL, Axis, ADD, and PD—and provides an example to help you enter your prescription correctly.
Important: The most common ordering mistake is selecting the wrong “+” or “−” sign.
Please pay close attention to the signs in front of the SPH and CYL values. For example, +2.00 and -2.00 are completely different prescriptions.
1. Understanding Your Prescription
Before entering your prescription, it is helpful to understand the abbreviations used for each eye:
- OD (Oculus Dexter): Right eye
- OS (Oculus Sinister): Left eye
Your right and left eyes may have different prescription values, so make sure you enter each value in the correct field.
A prescription may include:
- SPH (Sphere): Corrects nearsightedness or farsightedness.
- CYL (Cylinder): Corrects astigmatism.
- Axis: Specifies the orientation of the astigmatism correction.
- ADD(Addition): Adds extra power for reading or other near-vision tasks
- PD (Pupillary Distance): Measures the distance between your pupils and helps position the optical center of each lens correctly.
1.1 SPH (Sphere)
SPH, short for Sphere, indicates the lens power needed to correct farsightedness (hyperopia) or nearsightedness (myopia). It is measured in diopters (D) and is shown with a + or − sign.
Plus (+): Farsightedness
A plus (+) SPH value indicates farsightedness (hyperopia). This generally means nearby objects may be harder to focus on clearly, such as text on a phone, book, or computer screen.
Minus (−): Nearsightedness
A minus (−) SPH value indicates nearsightedness (myopia). This generally means distant objects may appear blurry, such as road signs, presentation screens, or objects across a room, while closer objects may be easier to see.
How to Enter SPH
Enter the SPH value exactly as shown on your prescription, including the + or − sign.
For example, +2.00 and −2.00 are completely different prescriptions, even though the number is the same.
Halliday G2 prescription lenses support SPH values from −9.00 D to +2.00 D, in 0.25 D increments, such as −1.00, −1.25, −1.50, and +1.75. Do not round or change your prescription value.
1.2 CYL (Cylinder)
CYL, short for Cylinder, indicates the amount of lens power needed to correct astigmatism.
Astigmatism occurs when the eye has an irregular curvature, which can cause blurred or distorted vision at different distances.
Like SPH, CYL is measured in diopters (D) and can have either a + or − sign, depending on how your prescription is written.
How to enter CYL
Enter the CYL value exactly as shown on your prescription, including the + or − sign.
Halliday G2 prescription lenses support CYL values from −3.00 D to +3.00 D, in 0.25 D increments.
Important: Do not enter an Axis value if your CYL is 0. Axis is only required when there is a cylinder correction.
1.3 Axis
Axis indicates the orientation of the astigmatism correction specified by your CYL value. It is measured in degrees, from 0° to 180°, and is shown as a whole number.
The CYL value tells you how much astigmatism correction is needed, while the Axis tells you where that correction is positioned.
How to enter Axis
Only enter an Axis value when your CYL value is not 0.
For example: CYL −0.75 / Axis 90°, which means the prescription requires −0.75 D of cylinder correction at an orientation of 90°. If your CYL is 0, you do not need to enter an Axis value.
Important: Some prescriptions may display Axis as 180 rather than 0. Enter the value exactly as it appears on your prescription.
1.4 ADD (Addition)
ADD, short for Addition, indicates the additional lens power needed for near vision, such as reading or viewing objects at close range.
ADD is commonly included in prescriptions for presbyopia, a condition that can make it more difficult to focus on nearby objects. It is usually shown as a positive (+) value.
Please note: Halliday G2 currently does not support progressive prescription lenses. If your prescription includes an ADD value for progressive lenses, this prescription type is currently not supported.
1.5 PD (Pupillary Distance)
PD, short for Pupillary Distance, is the distance between the centers of your pupils. It is measured in millimeters (mm).
PD helps ensure that the optical center of each prescription lens is positioned correctly in front of your eyes, which is important for clear and comfortable vision. Your prescription may show PD as either a Total PD or Monocular PD.
Total PD
Total PD is the distance between the centers of both pupils and is shown as a single number.
For example: PD: 63 mm
Halliday G2 prescription lenses support Total PD values from 56 to 74 mm.
Monocular PD
Monocular PD provides a separate measurement for each eye, measured from the center of the nose to the center of each pupil.
For example: Right: 31 mm / Left: 32 mm
Halliday G2 prescription lenses support Monocular PD values from 30 to 50 mm per eye.
How to Enter PD
Enter your PD exactly as shown on your prescription. If your prescription does not include a PD measurement, you may be able to obtain it from your optician or measure it yourself.
If you need to measure your PD yourself, please follow our [How to Measure Your PD] guide for step-by-step instructions.
2. Need Further Help?
If you have questions about your prescription or are unsure how to enter your prescription information, please click here to contact us, and we’ll be happy to help you understand the fields before you complete your order.
When contacting us, please attach an up-to-date copy of your eyeglass prescription. This will help our team review the information more efficiently and provide you with more accurate assistance.