Cataract surgery replaces the eye’s clouded natural lens with an artificial intraocular lens (IOL). While this procedure dramatically improves distance vision, it often changes the ability to focus on close objects. This alteration creates a new need for vision correction, specifically reading glasses, for many patients. Determining the correct power of these reading glasses depends on the specific IOL implanted and the individual’s visual goals.
Understanding Near Vision After IOL Implantation
The eye’s natural lens changes shape through accommodation, allowing it to shift focus between distant and near objects. This flexibility naturally declines with age (presbyopia). During cataract surgery, the natural lens is replaced with a fixed artificial IOL. Since a standard IOL cannot change shape, the eye loses its ability to accommodate and establishes a single clear focal point. If this point is set for distance vision, reading glasses are needed to optically shift the focal point closer for clear near vision.
How Different IOLs Affect Reading Glass Needs
Monofocal IOLs
The type of IOL implanted is the most significant factor determining reading glass needs and power. The most common option is the monofocal IOL, which provides clear vision at a single, predetermined distance, usually optimized for far viewing. Patients with monofocal lenses set for distance will almost certainly need reading glasses for any task within arm’s reach.
Premium IOLs
Premium lenses, such as multifocal or trifocal IOLs, are designed to provide clear vision at multiple distances (near, intermediate, and far). These lenses significantly reduce or may eliminate the need for reading glasses for most daily activities. Extended Depth of Focus (EDOF) IOLs create one elongated focal point that improves both distance and intermediate vision, though they may still require low-power reading glasses for very fine print.
Monovision
Another approach is monovision, which uses monofocal IOLs but sets one eye for distance vision and the other for near vision. This technique allows the brain to blend the two images, providing a wider range of focus without glasses for many people. While monovision reduces reliance on reading glasses, a person may still need them for prolonged reading or particularly small text.
Finding the Right Power: Testing and Prescription Strength
The power of reading glasses is measured in diopters (D), which express the lens’s optical strength. The required power relates directly to the preferred reading distance; a higher diopter means a shorter focal point. For most patients with distance-set monofocal IOLs, the required reading power is typically +2.00 D to +2.75 D. Lower powers (+1.00 D to +1.50 D) are often sufficient for intermediate tasks like computer work. The ultimate power is determined by a post-operative refraction test, though over-the-counter (OTC) readers may be adequate if distance vision is otherwise clear.
When to Purchase and Expect Stable Vision
The eye’s prescription is not immediately stable following cataract surgery, as the eye needs time to heal and adjust to the new lens. During this stabilization period, vision may fluctuate slightly. Most eye care professionals advise waiting until the final post-operative check-up before purchasing permanent, custom-ground reading glasses. This final prescription is usually given when vision is stable, typically two to six weeks after an uncomplicated surgery. If needed during the interim period, temporary OTC reading glasses can be used comfortably until the final, accurate prescription is determined.