Nearsightedness (myopia) is a common vision condition where distant objects look blurry, but objects up close appear clear. This occurs because the eye is either too long or the cornea is too steeply curved, causing light to focus in front of the retina. People who wear glasses to correct this blur often wonder if they should keep them on for close-up tasks like reading. The decision depends on how the corrective lens interacts with the eye’s natural focusing mechanism.
The Optical Principle of Nearsightedness and Reading
Lenses used to correct nearsightedness are negative (diverging) lenses, marked with a minus sign on a prescription. These lenses spread out light rays before they enter the eye, pushing the focal point backward onto the retina for clear distance vision. When looking at a distant object, the negative lens brings the nearly parallel light rays into focus correctly.
When looking at a near object, the eye uses accommodation to focus the light. This process involves the ciliary muscle contracting to make the eye’s natural lens thicker and more convex, increasing its converging power. However, the negative lens of a distance prescription counteracts this natural focusing effort because it diverges light, forcing the eye to work harder for clear near focus.
Wearing distance glasses for reading forces the eye to over-accommodate, meaning the ciliary muscle strains more than necessary to overcome the lens’s diverging effect. This excessive effort can lead to symptoms like eye fatigue, strain, and headaches after prolonged near work. The correction needed for distant vision is the opposite of what the eye needs for comfortable close-up vision.
When to Remove Your Glasses for Near Tasks
The decision to remove distance glasses for reading depends on the strength of the prescription and the working distance. For people with a moderate to strong nearsighted prescription, removing the glasses allows the eye’s focusing muscle to relax. Without the diverging lens, the slightly over-focused nearsighted eye can provide clear vision at a normal reading distance (around 14 to 16 inches).
For example, a person with a -2.00 Diopters (D) prescription has a natural clear point at about 50 centimeters, a comfortable reading distance. Wearing the full -2.00 D correction forces the eye to accommodate for the entire distance, creating strain. Conversely, if the prescription is mild, such as -0.75 D, the required over-accommodation may be negligible, and the wearer can comfortably keep the glasses on.
If the text is clear and comfortable without the glasses, removing them for reading or computer work is a simple way to reduce strain. Prioritize comfort; if keeping the glasses on for near tasks causes discomfort or forces you to hold material farther away, it is better to remove them. This action is not harmful to the eyes, but allows the eye’s natural mechanics to operate without interference.
Solutions for Complex Vision Needs
Simply removing distance glasses may not be enough for everyone, particularly after age 40, when presbyopia usually begins. Presbyopia is the age-related hardening of the eye’s natural lens, which reduces the ability to focus on near objects. A nearsighted person with presbyopia, who sees clearly up close without glasses, will eventually find that removing distance correction is no longer sufficient to bring text into focus.
For individuals who are both nearsighted and presbyopic, specialized corrective lenses are necessary to provide clear vision at all distances. One common solution is to use dedicated reading glasses, which feature a positive or plus power addition to aid near focus. These are often worn over contact lenses or used when the distance glasses are removed.
Alternatively, multifocal lenses combine the distance and near corrections into a single lens. Bifocals feature two distinct optical powers, separated by a visible line, with the distance correction on top and the reading correction on the bottom. Progressive lenses offer a more seamless transition, gradually changing from the distance prescription at the top of the lens to the reading prescription at the bottom. These solutions ensure that the eye receives the appropriate level of optical power to comfortably see objects both far away and up close.