Wearing glasses not meant for you generally falls into two categories: using someone else’s prescription lenses or trying on non-prescription eyewear, such as fashion frames or over-the-counter reading glasses. The risks and consequences of each scenario are different, ranging from mild temporary discomfort to significant visual disturbance. Understanding the customized nature of optical correction explains why lenses tailored for another person can quickly cause problems.
The Personalized Nature of Prescription Lenses
Prescription glasses are far more individualized than simply a number indicating the degree of nearsightedness or farsightedness. The prescription specifies the sphere (power), cylinder (astigmatism correction), and axis (orientation of the cylinder) for each eye independently. This detail is necessary because both eyes rarely require the exact same correction.
Beyond the power, a measurement called Pupillary Distance (PD) is incorporated to ensure proper manufacturing. PD is the distance between the centers of your pupils, which dictates where the optical center of the lens must be placed. The optical center is the point on the lens where light passes through without being bent or distorted.
Aligning the optical center with the pupil is necessary for clear, comfortable vision. If the lens is decentered, even by a few millimeters, the light passing through is refracted, inducing a prism effect. This prismatic distortion forces the eyes to work harder to fuse the image, which is the underlying reason for many of the physical symptoms associated with wearing the wrong glasses. Opticians often measure monocular PD to account for facial asymmetry, making the lens alignment unique to the wearer.
The Immediate Risks of Wearing Someone Else’s Prescription
Wearing another person’s prescription lenses is problematic because it forces the eye muscles to compensate for a mismatch in power and alignment. The most common consequence is eye strain (asthenopia), resulting from the constant muscular effort to achieve focus and overcome distortion. This strain often leads to frontal headaches and fatigue around the eyes.
When the lens power is incorrect, the eyes struggle to process a clear image, leading to a blurry or distorted view. The misalignment of the optical center with the pupil induces a prismatic effect that misplaces the image seen by each eye. This forces the eye muscles to constantly adjust the angle of the eyes to prevent double vision (diplopia).
The brain attempts to correct the visual mismatch, but this compensation frequently fails, leading to symptoms that interfere with normal function. People often experience dizziness, disorientation, and nausea, similar to motion sickness. While wearing someone else’s glasses will not cause permanent damage to an adult’s eyes, the discomfort and disruption can be severe and immediate. These effects increase with the difference in prescription power and the degree of PD misalignment.
Safety of Non-Corrective and Over-the-Counter Glasses
The risk profile changes dramatically when considering non-corrective glasses, such as fashion frames with plano lenses (zero power). These lenses are generally safe for the eyes because they do not alter how light enters the eye. Any discomfort is typically related to the physical fit of the frame or the quality of the lens material, which may cause minor distortions or glare if poorly manufactured. Some plano lenses, like those with a blue light filter, are designed to reduce eye strain from digital screens.
Over-the-counter (OTC) reading glasses, often called “readers,” contain magnifying power to help with close-up tasks (presbyopia). These glasses are mass-produced as a one-size-fits-all solution. They only correct for spherical power and do not account for astigmatism or differences in power between the two eyes. Furthermore, OTC readers use a standardized Pupillary Distance that will not precisely match the PD of most individuals.
For brief use, such as reading a menu or a price tag, the generalized power and PD of OTC readers are usually acceptable. However, prolonged use, like hours of reading or computer work, can still cause eye strain and headaches. This strain occurs because the eyes are forced to converge to overcome the standardized PD, or because one eye is over-corrected or under-corrected compared to the other. If relying on OTC readers for extended periods, a prescription pair with custom PD and individual lens powers provides a more comfortable and visually accurate experience.