Ordering prescription glasses online offers both convenience and potential cost savings compared to traditional retail. Success depends on possessing and accurately using a few specific pieces of information. Before selecting a frame or lens, you must gather your current optical prescription, an accurate measurement of your pupils, and the size specifications of a comfortably fitting frame. Having these details prepared ensures the final product provides the correct vision correction and a proper physical fit.
Obtaining and Interpreting Your Prescription
The fundamental document required is a current, valid prescription obtained from a recent eye examination. This document contains a series of numbers that instruct the lab on how to manufacture your corrective lenses. Online retailers will require you to input these figures exactly as they appear, or upload a copy of the official paper document.
The prescription is typically organized with separate entries for the right eye (OD, or oculus dexter) and the left eye (OS, or oculus sinister). The Sphere (SPH) value indicates the amount of lens power needed to correct for nearsightedness (indicated by a minus sign) or farsightedness (indicated by a plus sign). This is the core correction for distance vision, measured in diopters.
If you have astigmatism, which is an imperfection in the curvature of the eye’s lens or cornea, you will also see values for Cylinder (CYL) and Axis. The CYL value specifies the amount of corrective power required for the astigmatism. The Axis is a number between 1 and 180 degrees that shows the precise angle of that correction. Finally, if you need multifocal or progressive lenses for reading, a separate Add (ADD) power will be listed, which is the extra magnifying strength for near vision. The prescription must also be unexpired, as the strength of your vision correction can change over time.
The Critical Measurement: Pupil Distance (PD)
The Pupil Distance, or PD, is the measurement in millimeters of the space between the centers of your two pupils. This is a significant requirement for online ordering, as it dictates where the optical center of each lens must be placed. Correct lens centering is essential for clear vision and comfort.
An incorrect PD measurement, even by a millimeter or two, can lead to uncomfortable visual side effects such as eye strain, headaches, and general blurring because the eye is forced to look through a sub-optimal part of the lens. For this reason, the most reliable method for obtaining your PD is to request it from your eye care professional, although it is not always automatically included on the prescription slip.
If your doctor did not provide the PD, you can measure it yourself using a millimeter ruler and a mirror, or with the assistance of a friend. The measurement may appear as a single number (single PD), which is the total distance between the pupils. Alternatively, it can be listed as two separate numbers (dual or monocular PD), which measures the distance from the center of each pupil to the bridge of the nose. A dual PD is considered more accurate for lens alignment, particularly with stronger prescriptions.
Ensuring Frame Fit: Understanding Frame Measurements
After confirming the optical accuracy of your lenses with the prescription and PD, the next step is confirming the physical fit of the frame. Eyeglass frames are universally sized using three numbers, typically printed on the inside of the temple arm, with all measurements expressed in millimeters.
The first number is the lens width (eye size), which is the horizontal width of the lens opening and usually ranges from 40 to 60 mm. The second number is the bridge size, the distance between the two lenses where the frame rests on your nose, generally falling between 14 and 24 mm. A proper bridge fit prevents the glasses from sliding down or pinching the nose.
The third number is the temple length, the length of the arm from the hinge to the tip that wraps behind the ear. Common temple lengths range from 120 to 150 mm. The most effective way to ensure a comfortable fit for new frames is to find these three measurements on a pair of your existing glasses that you already find comfortable, then use those numbers as a reference point for your online selection.
Final Steps: Selecting Lenses and Completing the Order
With your prescription, PD, and frame measurements secured, the final stage is selecting the lens material and coatings before checkout. The choice of lens material should correspond to your prescription strength and lifestyle, as different materials offer varying levels of thinness and impact resistance.
Polycarbonate lenses are highly impact-resistant, making them suitable for active individuals, especially those with mild to moderate prescriptions. For stronger prescriptions, high-index plastic lenses are recommended because they are designed to be much thinner and lighter than standard lenses, which helps reduce the bulky appearance often associated with high power correction.
You will also need to choose from various lens coatings that enhance performance. An anti-reflective (AR) coating is beneficial for reducing glare from computer screens and headlights. A blue light filter can help decrease eye strain during prolonged digital device use. Before finalizing your transaction, review the retailer’s return and exchange policy carefully, confirming that all your entered data is accurate before clicking to submit the order.