Prescription Lenses
Prescription lenses are customized lenses based on the results of an individual's eye examination, used to correct vision problems such as myopia (nearsightedness), hyperopia (farsightedness), astigmatism, or presbyopia. The parameters for prescription lenses are determined by a professional optometrist or ophthalmologist. Each person's prescription is unique, ensuring the wearer achieves optimal visual clarity.
What parameters are included in a prescription?
Your glasses prescription (Prescription) will typically include:
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SPH (Sphere): The degree of nearsightedness or farsightedness.
- A minus sign (-) indicates nearsightedness.
- A plus sign (+) indicates farsightedness.
- CYL (Cylinder): The degree of astigmatism.
- AXIS(Axis): The axis orientation for astigmatism ( 0° – 180° ).
- ADD (Addition): The additional power for reading, used in bifocals or progressive lenses for presbyopia.
- PD (Pupillary Distance): The distance between the centers of your pupils.
Detailed Parameter Explanation
SPH (Sphere)
The spherical power is a numerical value that measures the lens's corrective ability to address focusing problems. Specifically:
- Plus Power (e.g., +2.00): For individuals with farsightedness (hyperopia), helping them see nearby objects clearly.
- Minus Power (e.g., -1.50): For individuals with nearsightedness (myopia), helping them see distant objects clearly.
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Zero Power: Sometimes noted as "Plano" or "infinity", indicating no vision correction is needed.
This value is measured in Diopters (D), typically adjusted in increments of 0.25. Our lenses support a power range from +12.00 D to -12.00 D, precisely meeting the vision needs of different users.
CYL (Cylinder) & AXIS(Axis)
Cylinder (CYL) and Axis (AXIS) are two key parameters used to correct astigmatism. So, what is astigmatism? Astigmatism is a vision condition caused by an irregularly shaped cornea (more like a football than a perfect basketball). This causes light to focus on multiple points instead of a single point on the retina, resulting in blurred or distorted vision.
It is particularly important to note: If your prescription includes a Cylinder (CYL) value, it must be accompanied by a corresponding Axis (AXIS) value. These two parameters are inseparable.
【Parameter Details】
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CYL (Cylinder): Indicates the corrective power for astigmatism.
- Can be left blank (indicating no astigmatism).
- Can be a positive or negative value.
- Measured in Diopters (D).
- Common range: ±0.25 to ±4.00, with 0.25 as the smallest adjustment unit.
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AXIS: Indicates the orientation or meridian of the astigmatism correction.
- Range: 0° - 180°.
- Always appears paired with a Cylinder power.
ADD (Addition)
The Addition (ADD) refers to the extra corrective power provided for near vision tasks, like reading. It essentially adds a "magnifying function" on top of your distance prescription. This parameter is common in reading glasses, bifocals, or progressive lenses.
Specifically:
- Function: Adds additional power to your distance prescription specifically for viewing close objects, meeting the needs for activities like reading or using a smartphone.
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Value Characteristics:
- Typically the same value for both eyes; the prescription may note it once but it applies to both.
- Measured in Diopters (D).
- Common range is between +0.50 D and +3.50 D, adjusted in 0.25 increments.
- Applicability: This parameter is only relevant if your glasses need to cater to both distance and near vision. If the glasses are purely for distance, this value is not needed.
- Notation: Different optometrists may use terms like "ADD" or "Near" to indicate the addition power.
- Note: Even realities single vision lenses do not support ADD customization. If needed, please contact an Even Retail store for consultation.
PD (Pupillary Distance)
Pupillary Distance is the distance between the centers of your pupils, ensuring the prescription lenses are correctly centered in front of your eyes.
For adults, PD typically ranges from 60 mm to 66 mm (see chart). While 63 mm is a common average, we recommend you obtain this measurement from your optometrist.
Prism Lenses
Prism lenses are used to correct focusing alignment issues of the eyes, often playing a significant role in treating strabismus (misaligned eyes) or problems with binocular vision coordination. They work by bending the path of light to help the eyes align better.
*Even Realities website does not support the production of lenses with prism correction. If required, please contact our Even Retail store for consultation.