Monovision Articles What is Monovision ?

Monovision is the situation where the focus of one eye is set for distance and the focus of the other eye for near. This is one way of dealing with the middle age loss of near vision. Monovision is a strategy for reducing dependence on reading spectacles.

In the youthful eye there is a natural ability to adjust focus from distance to near. This is gradually lost with advancing years. In children the natural lens within the eye is very pliable and a muscle acts upon it to change its shape. As the lens changes shape so the focus of the eye is altered. This is why young children, who can see clearly in the far distance, can also see clearly just inches from their nose. Unfortunately the lens becomes stiffer with ageing and, although the muscle still works, it is less able to modify the lens shape. By mid forties the focusing reserve of the eye has diminished so that when tired or in poor light clear near vision cannot be achieved or sustained. Near vision spectacles become necessary. This declining focus adjustment of the eye is called "loss of accommodation", and the age related inability to see at near is called "presbyopia". Science has not yet come up with a way of truly restoring the youthful focus adjustment to the eye.

Monovision is a way of overcoming this problem. It is a compromise. A deliberate difference is created between the two eyes. One eye has clear distance vision whilst the other eye has clear near vision. Some individuals adapt to this and some do not. Monovision "works" when the individual is forgetful or unaware of the difference between the eyes and just attends to the image that is in best focus. As gaze changes from distance to near the brain must flip from attending to the image from one eye to that of the other. The person lives with both eyes open and sees with whichever eye has clearer vision. Of course the eye that is a little out of focus is still contributing to vision. How long it takes to get used to this new way of seeing varies from one person to another. There is a spectrum of experience. Some take to it almost immediately but at the other extreme some never seem to be able to overcome the awareness that one eye is blurred.

For monovision to be a success both eyes must have about equal best vision. If one eye has significantly poorer best vision (e.g. is a "lazy eye") the brain will struggle to hand over visual attention from one eye to the other. It will always want to see with the better eye.

Monovision can deliver social independence from reading spectacles. By this I mean the ability to see mobile phones, ones wristwatch, shop prices and restaurant menus. It is rarely as good as near vision with spectacles. This is because with specs' both eyes are being used to read and with the full correction. With monovision only one eye is in focus for near and usually the correction is toned down a bit to avoid creating too great a difference between the eyes.

Monovision may not give total independence from spectacles. There may be some situations where it is preferable to have the eyes in synchronous focus. One example is driving at night. With monovision one eye will have blurred distance vision. Oncoming headlights will form starburst images in that eye which may be distracting. The solution is to use spectacles that refocus that eye for distance. When reading challengingly small print for extended periods spectacles may provide more acceptable near vision.

Monovision can be achieved with contact lenses or various forms of eye surgery. This can be laser (e.g. LASIK, LASEK, Epi-LASIK or PRK), Conductive Keratoplasty (CK), or for errors too great for laser correction Refractive Lens Exchange is an option. If surgery is being considered it is wise to have a contact lens trial of monovision first to be as sure as possible that one will adapt to it.

Monovision rarely works well in spectacles because of the unequal magnification caused by different lenses when placed away from the eye.