Eye fatigue, or asthenopia, is a common complaint experienced after prolonged visual tasks, manifesting as tired, burning, or aching eyes. While corrective lenses are designed to alleviate strain, sometimes the glasses themselves cause discomfort. Feeling tired while wearing glasses signals a mismatch between the visual system and the corrective lens, forcing the eye muscles or the brain to overcompensate. This article explores the most common reasons why corrective lenses may cause eye fatigue.
Problems with Lens Power
The most direct cause of eye fatigue is an inaccurate or outdated prescription, meaning the lens power does not perfectly correct the eye’s refractive error. When a prescription is slightly too strong (overcorrection) or too weak (undercorrection), the internal ciliary muscles must work harder to achieve a clear image. This continuous muscular effort leads to fatigue, resulting in symptoms like headaches and eye soreness.
Astigmatism correction, managed by the cylinder and axis components of a prescription, presents another fatiguing issue. The axis dictates the precise angle at which the lens must be oriented to neutralize the eye’s irregular curvature. If the axis is off by even a small amount, especially with high cylinder power, the eye muscles strain continuously to rotate the image for clarity. This constant attempt to stabilize the visual field contributes to discomfort and headaches.
Frame Fit and Optical Center Issues
Even if the lens power is perfectly accurate, the physical placement of the lenses within the frame can induce significant eye strain. Every prescription lens has a specific optical center, the point where light passes through without being bent or refracted. This optical center must be aligned precisely with the wearer’s Pupillary Distance (PD), the measurement between the centers of the pupils.
When the optical center of the lens does not line up with the pupil, the prismatic effect occurs. The eyes are forced to constantly converge (turn inward) or diverge (turn outward) to look through the correct part of the lens, rather than the intended optical center. This unwanted prism effect is a direct strain on the extraocular muscles, which control eye movement, leading to headaches, double vision (diplopia), and generalized discomfort. Decentration by as little as 3.5 millimeters can induce enough unwanted prism to cause asthenopic symptoms.
The physical fit of the frame also plays a role in shifting this alignment. If the frames are loose, slide down the nose, or sit tilted, the optical center is constantly displaced from the intended position in front of the pupil. This misalignment forces the eyes to adjust to a new line of sight, which is fatiguing and can negate the benefits of an otherwise perfect prescription.
Adaptation and Digital Strain
When a person begins wearing a new pair of glasses, a temporary adjustment period is necessary, during which eye strain is common. For most people, this period lasts between a few days to two weeks, as the brain learns to process the new visual input. Symptoms can include mild dizziness, a sense of warped perception known as the “fishbowl effect,” and headaches.
Lenses with more complex designs, such as progressive lenses or those with a significant change in prescription, require a longer adaptation time. Progressive lenses feature a seamless transition of power for distance, intermediate, and near vision, introducing peripheral distortion the brain must learn to ignore. The wearer must also learn new movement patterns, shifting the head and eyes to look through the correct focal zone.
Beyond the initial adjustment, prolonged use of digital screens can exacerbate eye fatigue, even with the correct prescription. Digital eye strain occurs because looking at a screen often reduces the blink rate and requires the eyes to focus intently on an intermediate distance for extended periods. If a prescription is optimized for distance but not specifically for the intermediate range of a computer monitor, the eye muscles must strain to maintain focus. This effect can be mitigated by using specialized computer lenses or by ensuring lenses include an anti-reflective (AR) coating, which reduces glare and reflections from screens and overhead lighting. Following the 20-20-20 rule—looking at something 20 feet away for 20 seconds every 20 minutes—can also provide relaxation for the focusing muscles.