Monovision is a method of allowing patients to avoid the use of reading glasses. It is a type of ‘workaround’, and not really a solution to the underlying problem, which is called ‘Presbyopia’.
What is Presbyopia?
Presbyopia is the only disease known to affect 100% of the human population. This is because it is an aging change in the eye, that appears to be irreversible and progressive. In presbyopia, which means ‘aging vision’, the loses the ability to focus on intermediate and near objects. It usually begins when patients are in their early 40’s, and progresses to the point of needing reading glasses by the time patients are 47 years of age.
What is the cause of Presbyopia?
There is controversy regarding the cause of Presbyopia, but it is believed that 2 changes in the lens of the eye lead to the loss of ability to focus on near objects:
- Hardening of the lens of the eye
As we age, the lens of the eye hardens and thickens. In most cases, there is cataract forming in the lens as well. As this occurs, it becomes more diffictult for the muscles of the eye to flex and change the shape of the lens.
- Enlargement of the lens
As the lens hardens and thickens, it fills more space inside the eye. In this environment, there is not enought room between the inside wall of the eye and the edge of the lens of the eye for the muscles of focus to flex fully. This reduces the ability to focus the eye.
How is Presbyopia treated?
There is no way to treat Presbyopia. The aging process that causes the loss of focus cannot be reversed or treated directly. There are, however, some ways to allow function for near work:
In this situation, the dominant eye is corrected for distance, and the non-dominant eye is corrected for near. This can be accomplished through the use of contact lenses, or surgery. LASIK patients often choose this option.
- Reading glasses, bifocals and bifocal contact lenses
Glasses that provide magnification for reading work very well, but they are a hassle. Since they are not needed all of the time, patients tend to lose them very frequently. Bifocals allow full time wear of glasses, with distance correction in the top part of the glasses lenses, and the reading ‘add’ built into the bottom area.
- Lens Implants
Modern lens implant surgery can allow placement of lens implants that allow a full range of vision without glasses. This surgery is called ReLEx.
More on Monovision
Monovision is a very successful means of avoiding reading glasses and enabling near vision. It does, however, have several downsides or pitfalls:
- Loss of Depth Perception
Depth perception depends on both eyes working together. Most monovision patients notice this when driving, but most usually learn to compensate with time.
- Decreased Night Vision
Creating monovision means that one eye is made nearsighted (unable to see distance). This issue is accentuated at night, and can be bothersome for many patients.
- “I Can See But” Syndrome
Monovision patients will very often say “I can see, but it is not clear”. Our brains are wired to use both eyes to obtain the sharpest vision. When this is interrupted, many patients are bothered by it. Most will overcome this problem as well.