Headaches while wearing glasses, but not contacts, are a common frustration for people needing vision correction. This difference occurs because glasses and contacts are fundamentally distinct optical devices, even when sharing the same prescription. The physical separation of the spectacle lens from the eye, the mechanical structure of the frame, and the brain’s unique processing of visual input introduce variables that can lead to significant eye strain and subsequent headaches. Understanding these differences helps pinpoint the source of discomfort.
The Optical Difference in Lens Placement
The most significant optical distinction lies in the vertex distance, which is the space between the back surface of a spectacle lens and the front of the eye’s cornea. Contact lenses sit directly on the cornea, resulting in a near-zero vertex distance, while glasses typically rest about 12 to 14 millimeters away. This separation changes the lens’s effective power, especially for higher prescriptions exceeding \(\pm 4.00\) diopters.
For strong prescriptions, the necessary power adjustment is calculated to compensate for this distance. If the glasses are worn closer or farther than this calculated measurement, the optical correction is inaccurate. This forces the eye muscles to work overtime to maintain focus, and this constant muscular effort leads to eye strain and tension headaches.
Another element is the difference in the field of view. Glasses provide a clear view through the center of the lens, but the periphery can cause distortions or blurring that the brain must filter out. Because a contact lens moves with the eye, the wearer always looks through the lens’s optimal center. This eliminates peripheral distortion and results in a more natural, uniform visual experience.
Physical Fit and Alignment Issues
Headaches caused by glasses often originate from the physical apparatus itself, a problem contacts entirely circumvent. The frame’s fit can create mechanical tension headaches if frames are too tight. Pressure points include the temples, the sides of the head behind the ears, or the bridge of the nose.
This sustained pressure on nerves and blood vessels can trigger a tension-type headache unrelated to the prescription. Adjustments to the temple arms, nose pads, or overall frame width can frequently resolve this issue. Heavier frames or those with improper weight distribution are also more likely to cause external pressure.
A primary issue is the alignment of the Optical Center (OC) of the lens. The OC is the point where light passes through without being bent, and it must align precisely with the wearer’s pupil. If the pupillary distance (PD) measurement is incorrect, the OC will be misplaced, forcing the eye to look through a slightly prismatic area of the lens. This prismatic effect causes the eyes to constantly strain to fuse the two slightly separated images, which is a major source of debilitating eye strain and headaches unique to poorly fitted glasses.
When the Prescription Requires Adaptation
When a new prescription is introduced, the brain and visual system require an adjustment period to adapt to the altered visual input. This is common even with an accurate prescription, especially if the change in power is significant. Temporary headaches, mild dizziness, or disorientation can occur during the first few days to two weeks as the brain recalibrates to the new focal point.
Small errors in astigmatism correction, known as the cylinder axis, are significantly more impactful in glasses. Astigmatism correction uses a cylindrical lens to focus light along a specific axis. If this axis is even a few degrees off in the fixed spectacle lens, the eye is forced to constantly twist and refocus, leading to intense eye strain. While toric contact lenses stabilize on the eye and may rotate slightly, the continuous, fixed error from a misaligned spectacle lens is often a greater headache trigger.
Specialized lenses, such as progressive or multifocal lenses, compound this adaptation challenge. These lenses contain multiple prescriptions for distance, intermediate, and near vision within a single lens. The wearer must learn new head and eye movement patterns to find the correct viewing zone, which demands significant coordination. This process can initially cause visual stress and headaches that contacts, which are typically single-vision or have gradual multifocal zones, do not impose.
The need for prescribed Prism is another factor unique to glasses. Prism corrects subtle eye misalignment issues, known as binocular vision dysfunction, by bending light to allow the eyes to work together comfortably. Complex or higher prism amounts are typically only possible in spectacle lenses. If an individual has an uncorrected need for prism, or if the prescribed prism in their glasses is inaccurate, the eyes will struggle to fuse the images, resulting in headaches, dizziness, and nausea.