The ability of the eye to focus on close objects naturally decreases with age, a condition known as presbyopia. This makes it difficult to shift focus between distant and near viewing distances. Monovision is a strategy used to address this issue by altering the vision in each eye to function differently. One eye is corrected for clear distance vision, while the other eye is corrected to see clearly at a near distance. The brain is then tasked with choosing the clearer image based on the object’s distance, providing functional vision without constant reliance on corrective lenses.
Understanding Monovision Mechanics
Monovision relies on the brain’s capacity for neuro-adaptation to blend the two different visual inputs. The strategy typically involves correcting the dominant eye for distance viewing and the non-dominant eye for near tasks. When viewing a distant object, the brain preferentially uses the sharp image from the distance-corrected eye and suppresses the slightly blurred input from the near-corrected eye.
Conversely, when focusing up close, the brain favors the sharp image relayed by the near-corrected eye, ignoring the distance eye’s blurry input. This process of suppression and selection allows a person to function across a range of distances without constantly changing correction. However, this intentional blurring means that full binocular vision, where both eyes contribute equally to a sharp image, is not maintained at any single distance. This compromise can lead to reduced depth perception and contrast sensitivity.
The difference in focus between the two eyes can also introduce issues where the brain miscalculates the depth or speed of moving objects. Despite these trade-offs, many individuals successfully adapt to monovision, using it as a practical way to reduce their dependence on reading glasses. A trial period using temporary correction is often recommended to ensure the brain can successfully manage the disparate information and achieve a comfortable, functional blend.
The Direct Answer Monovision Using Standard Eyeglass Lenses
While it is technically possible to order a pair of eyeglasses with two different single-vision prescriptions—one for distance and one for near—this is generally not a recommended or successful approach for true monovision. The fundamental difference between an eyeglass lens and a contact lens is their position relative to the eye. A contact lens moves with the eye, ensuring the optical center of the correction is always directly over the pupil.
Eyeglass lenses, however, are fixed in an immobile frame, which creates significant optical challenges when the prescriptions are drastically different. As the eye rotates to look through any part of the lens other than the precise optical center, the difference in prescription between the two lenses induces unequal prismatic effects. When this is unequal between the two eyes, it forces the eye muscles to work harder to align the images.
This constant, unnatural muscular effort can lead to visual strain, headaches, and even diplopia, or double vision. Furthermore, having two lenses of significantly different powers can cause a noticeable difference in image size, a condition called aniseikonia, which the brain struggles to fuse. Because glasses require the eyes to work binocularly through a fixed lens, the induced problems often outweigh the benefit of the monovision effect.
For this reason, most eye care professionals do not prescribe monovision in spectacle lenses, reserving the technique almost exclusively for contact lenses, laser surgery, or intraocular lens implants. The fixed nature of the glass lens fundamentally disrupts the precise visual balance that monovision requires for comfortable adaptation.
Eyewear Alternatives for Presbyopia Correction
Since true monovision is optically problematic with traditional eyeglasses, several other eyewear solutions are routinely used to correct presbyopia.
The most common and sophisticated option is the Progressive Addition Lens (PAL), also known as a progressive lens. These lenses offer a seamless transition of power, starting with the distance prescription at the top, gradually shifting to an intermediate power in the middle, and ending with the full reading power at the bottom. Progressive lenses allow the wearer to see clearly at multiple distances by simply moving their gaze up or down through the lens, mimicking the eye’s natural ability to accommodate. This design maintains binocular vision by keeping the power changes smooth and symmetrical across both lenses, avoiding the image disparity issues associated with monovision in glasses. The trade-off is the presence of slight peripheral distortion on the sides of the lens that requires a period of adaptation.
Another common alternative involves segmented lenses, such as bifocals or trifocals. Bifocals have a distinct line separating the distance correction in the main part of the lens from a small segment containing the near correction. Trifocals add a second line and a segment for intermediate viewing.
A simpler but effective approach is the use of multiple single-vision pairs. This involves wearing one pair of glasses for distance activities and then either switching to a separate pair of dedicated reading glasses for near tasks. This functional method provides the widest, clearest field of view for each specific distance, even if it is less convenient than having all corrections in a single frame.