Putting on prescription glasses often brings distant objects into sharp focus, but leaves close objects, like a phone or book, blurry. This is not due to an incorrect distance prescription, but rather an age-related vision change called presbyopia. Presbyopia, which means “old eye” in Greek, is a universal condition that progressively affects the eye’s ability to focus on near objects. It typically begins to make close work difficult around the age of 40 to 45, regardless of any pre-existing vision problems. The corrective lenses worn for distance address only one type of focusing error, while reading difficulty is caused by a separate physiological change inside the eye.
How the Eye Loses Near Focus
The ability to focus on close objects is a dynamic process known as accommodation, which is performed by the eye’s internal lens. To achieve clear near vision, the ciliary muscle surrounding the lens contracts, causing the tension on the zonular fibers that hold the lens to relax. This relaxation allows the naturally elastic crystalline lens to spring into a thicker, more curved shape. The increased curvature of the lens boosts the eye’s refractive power, shifting the focal point forward onto the retina to render a sharp image of the nearby object.
This process of accommodation begins to decline surprisingly early, with the amplitude of focus decreasing from early adulthood. Presbyopia develops because the crystalline lens gradually loses its natural elasticity and flexibility over time. The lens fibers become more compacted and rigid, making the lens harder and less responsive to the action of the ciliary muscle. Even when the ciliary muscle contracts fully and the zonules relax, the hardened lens can no longer achieve the necessary curved shape to sufficiently increase the eye’s power for close focusing.
The result is that the near point, the closest distance at which an object can be clearly focused, moves progressively farther away from the eye. By the mid-forties, this near point moves beyond a comfortable reading distance of about 14 to 16 inches, leading to blurred vision for tasks like reading small print. The lens cannot generate the additional refractive power needed to bring light rays from close objects into focus on the retina.
Distinguishing Distance Correction from Near Vision Issues
Distance glasses correct a refractive error that affects distant vision, such as myopia (nearsightedness) or hyperopia (farsightedness). Myopia occurs when the eye is too long or the cornea is too curved, causing light to focus in front of the retina, which is corrected with a negative-power lens. Hyperopia results from an eye that is too short or a cornea that is too flat, causing light to focus behind the retina, which is corrected with a positive-power lens. Presbyopia, by contrast, is not a structural issue of the eyeball shape but a loss of function in the internal lens.
Distance glasses shift the focal point of the world onto the retina, but they do nothing to restore the lost flexibility of your lens for near focus. A person who is nearsighted may notice they can see up close better if they remove their glasses, a phenomenon called “myopic compensation.” This occurs because the uncorrected nearsighted eye is naturally focused closer than a normal eye. Removing the negative-power distance lens allows the eye’s inherent near focus to partially compensate for the lack of lens flexibility.
The distance prescription is designed to make light from far away objects converge on the retina. When looking at something up close while wearing them, the lack of accommodation is fully exposed. The distance prescription forces vision to its farthest point of focus, and the stiffening lens cannot add the extra power needed to bring the near object into focus. This results in clear distance vision and blurry near vision while wearing the same pair of glasses.
Options for Clear Up-Close Vision
Addressing presbyopia requires adding the missing positive refractive power that the aged lens can no longer provide. The simplest solution is single-vision reading glasses, which contain a fixed positive power to magnify and focus objects at a set reading distance. These are taken off for distance viewing, as the added power would make far objects blurry. This constant on-and-off exchange can be inconvenient for many people.
A full-time solution involves multifocal lenses, which incorporate both distance and near prescriptions into a single lens. Bifocal lenses provide two distinct power zones separated by a visible line: distance correction on top and reading correction on the bottom. Trifocal lenses add a third segment for intermediate viewing distances, such as a computer screen. Both bifocals and trifocals can cause an image “jump” where the distinct power zones meet, which some users find disruptive.
A more modern and visually seamless option is the progressive lens, sometimes called a no-line bifocal. This lens contains a gradual power change that transitions smoothly from distance correction at the top, through an intermediate zone, to the full reading power at the bottom. The continuous gradient provides clear vision at all distances without visible lines, mimicking more natural vision. For contact lens wearers, monovision corrects the dominant eye for distance and the non-dominant eye for near, relying on the brain to selectively use the clearest image.