Pupillary distance (PD) is the measurement between the centers of your pupils, typically expressed in millimeters. This detail ensures your eyeglasses provide clear, comfortable vision. When lenses are manufactured, their optical centers must align precisely with your pupils. An accurate PD measurement ensures you look through the optimal part of your corrective lenses.
Common Signs of Incorrect Pupillary Distance
Wearing glasses with an incorrect pupillary distance can lead to various symptoms and discomfort. Individuals may experience eye strain, which can manifest as a feeling of fatigue or aching around the eyes. Headaches are another frequent symptom, often described as frontal or around the temples, and these symptoms tend to worsen with extended wear of the glasses. Visual disturbances are also common, including blurry vision, especially when attempting to focus on objects, distortion, dizziness, disorientation, and in some cases, double vision.
How Optical Lenses Are Affected
Issues from incorrect PD stem from how light interacts with lenses, which have an optical center where light passes through without bending. If your pupil is not aligned with this optical center, you are effectively looking through a different part of the lens, which creates a “prism effect.” Light rays passing through the lens are bent, or deviated, towards the thicker part, forcing your eyes to converge or diverge more than they naturally would. This constant effort to compensate for the induced prism puts extra stress on the eye muscles, leading to eye strain, headaches, and distorted vision. Even a small error, such as a millimeter or two, can create noticeable issues, particularly for individuals with higher prescription strengths.
Steps to Take If Your PD is Wrong
If you suspect your glasses have an incorrect pupillary distance, take prompt action to alleviate discomfort. Contact the optician or retailer where you purchased the glasses, explaining your symptoms, as these are often clear indicators of a PD issue. Have your pupillary distance re-measured by a professional; opticians use specialized tools like pupillometers for precise measurements. Based on the re-measurement, they can determine if your current lenses need adjustment or if new lenses are required to correct the misalignment. Continuing to wear glasses with an incorrect PD can worsen symptoms.
Ensuring Accurate Pupillary Distance
To prevent incorrect pupillary distance issues, prioritize accurate measurements for future eyeglass purchases. Always have your PD measured by a qualified eye care professional during a comprehensive eye examination; they use precise methods and equipment. There are two main types: binocular (total distance between pupils) and monocular (distance from each pupil to the bridge of the nose), with monocular often being more accurate due to accounting for slight asymmetries. While self-measurement tools exist, professional measurement is superior, especially for multifocal lenses. Always ask your eye care provider for your PD measurement for your records.