If you are between 40 - 45 years of age and wear glasses for distance, you may have started to need help for reading / near vision too. This is usually addressed by changing your single vision spectacle lenses to bifocal lenses or varifocal lenses. If you don't or have never worn distance glasses, by the time you reach 40 -45 years of age you will still develop the need for reading / near vision glasses as this is due to the natural ageing of your eyes.
For patients in this age category who are considering laser eye treatment, and who want independence from both distance & reading glasses, the only viable option is monovision.
However, this isn't always entirely possible as most people usually have two different visual needs - your distance vision & your near vision. This guide will explain monovision in more detail.


Monovision is the solution whereby the focus of one eye is set for distance and the focus of the other eye for near. This is a strategy for reducing dependence on reading spectacles whilst not overly compromising distance vision.

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 and young adults 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 and young adults, 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 and 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 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. Some people take to it almost immediately but others never seem to be able to overcome the awareness that one eye is blurred.

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 reading glasses 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.

The important thing to understand when deciding if monovision is for you, is to accept that you may not have perfect distance vision AND perfect near vision. It is a compromise. Patients who adapt best are the ones who have a realistic expectation of the outcome. For most, monovision gives them independence from distance and near glasses for the vast majority of the time, however they accept that visual aids may be required for challenging distance and near tasks. As you continue to get older, your near vision will continue to diminish so you need to think of monovision as turning the hands back on a clock... we can re-set you, but we can't stop the clock ticking... However, the benefit you achieve from monovision will always be 'in the bank' so even you do require additional assistance for near vision in the years to come, the benefit of your monovision will still provide a degree of independence.
If laser treatment is being considered, it is wise to discuss this with your ophthalmologist at your consultation and to have a contact lens trial of monovision first to be sure that you can adapt to it. We can arrange this for you with Martin, our contact lens practitioner.
Monovision can be achieved with using the LASIK, LASEK, Epi-LASIK methods of refractive surgery.

I hope this guide has helped explain what monovision is and what it can achieve. If you would like any further information, please do not hesitate to contact one of the team here and we will be happy to discuss this in more detail.



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

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