Monovision Articles What is Monovision ?

Monovision is a fairly common medical technique ophthalmologists use to correct the effects of presbyopia. Presbyopia is a fairly naturally occurring phenomenon that comes with age, specifically the gradual loss of the eye's ability to change focus for close-up tasks like reading. The most common accepted theory about presbyopia (and thus the possible need for monovision with Lasik or other means) is that the aging eye starts to lose elasticity in its crystalline lens, or possibly changes in the curvature of the lens.

Monovision and Lasik

What the eye professional will do is to correct the vision of the presbyopic patient by adjusting one eye for near viewing and one for distance viewing. This used to be done primarily with contact lenses; the doctor would fit one eye with a lens to correct the near vision, and the other eye with a different prescription to correct the far vision.

The idea is the same with Lasik - one eye is operated on to correct the farsightedness, and one the nearsightedness. In other words, the goal is to operate for vision worse than 20/20.

The problem with this is that because each eye is corrected for different distances, the two eyes cannot work in tandem anymore, resulting in poor quality of vision and a depth perception decrease. Brightness helps this resulting monovision by shrinking the iris. However, it's worse and more noticeable in environments with low light and in instances when very sharp vision is required, such as reading small print for long periods of time or night driving.

Also, there is the possibility that - because it's not always clear how slow or fast the muscles of each eye will grow or change with age - Lasik surgery for other eye symptoms could result in the inadvertent result of monovision.

Considerations for Those With Monovision

If you are considering monovision through Lasik surgery, it is really important to talk to two or three well-regarded ophthalmologists to have a thorough check up. One needs to know how much his or her presbyopia might or might not increase in the future, and whether his or her eye(s) can tolerate a second or third procedure to correct any problems later.

Often times patients are unsure whether they would prefer to have their eyes surgically corrected so they have to work in tandem (thus monovision) or just have both eyes corrected to see equally. There are costs and benefits with both; it really depends on your doctor's assessment of your eyes and your personal habits.

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.

There are several ways of fitting contacts for patients who require a bifocal. Bifocal contacts, of course, are one option. Other options include a monovision contact lens fit, modified monovision, and a combination of distant vision contacts and reading glasses. I will discuss these options further, along with my impressions of the advantages and disadvantages of each.

Bifocal Contact Lenses

Bifocal contact lenses allow patients to see both distant and near at the same time. They are available in both soft and rigid gas permeable material.

The main advantage of bifocal contacts is better depth perception at both near and far. This is especially true when compared to monovision. Disadvantages include increased glare at night and a possible compromise in either the near or distant vision. The latter has been my experience with the soft simultaneous vision bifocal contacts (see below). It can be very difficult to achieve both good near and distant vision with these lenses. It seems that if we get the distant vision in good focus, the near vision suffers and vice versa. In these cases, I will sometimes try the modified monovision option (see below).

Within the category of bifocal contact lenses, there are simultaneous vision and translating (also know as alternating) bifocal contacts.

Simultaneous Vision Bifocal Contact Lenses

For simultaneous vision bifocal contact lenses, patients receive images from multiple distances at the same time. The brain must then choose which images to ignore based on the distance to the objects. The variety of lens designs available allow for near, intermediate, and distance vision correction. Simultaneous vision bifocal contact lenses are available in both soft and gas permeable materials. This category can be further broken down into aspheric, concentric, and diffractive lenses.

Aspheric Lenses

Aspheric contact lenses use a technology that creates a multifocal effect. What you need to know here is that these lenses produce an effect comparable to the progressive bifocal that is popular in spectacles. Some lenses within this category favor the distance vision, while others favor the intermediate or near vision. All these lenses, however, should yield some intermediate correction.

Picking the best lens depends on a patient's occupational demands (among other things). I have had some with both Bausch & Lomb's Soflens Multifocal as well as Ciba's Focus Progressive contacts.

Concentric Lenses

Concentric contact lenses have a central distance or near zone followed by one or more "rings" of the opposite power. One of the more popular lenses in this category is the Acuvue Bifocal made by Vistakon which is owned by Johnson & Johnson). I've had fairly good success fitting this lens (around 60% success rate). However, concentric contact lenses do not correct for the intermediate vision as well as the aspheric lenses do.

Diffractive Lenses

Diffractive contact lenses diffract ("splits") light entering the eye into different images depending on image distance. Cooper Vision's Echelon is the primary lens of choice in this category. I personally have never fit this lens, but I have colleagues who have with fairly good success.

Translating (Alternating Image) Bifocal Contact Lenses

The translating bifocal contact lenses design is similar in concept to the bifocal you see in an individual's glasses. There are specific areas for the distance and near correction. Typically the top of the lens is the distance correction, with the near being in the lower portion. To view items at near, the patient must look down, thereby placing the near correction in front of the pupil. One of the more popular lenses in this category would be the Tangent Streak made by Fused contacts. This lens is available in both bifocal and trifocal prescriptions.

The primary disadvantage of the translating bifocal contact lens is that, as with spectacles, the patient must move his/her eyes downward to use the near portion of the lens. Therefore, this design is not a good option for those individual's who need to view close objects at the straight ahead position.

Monovision

Monovision contact lens wear is where one eye - usually the dominant eye - is corrected for distant vision and the other eye is corrected for near vision. When the patient views objects in the distance, the brain learns to suppress (at least this is the goal) the image in the eye corrected for near vision and vice versa.

Wearing a monovision contact lens correction is a good option for those patients who cannot wear a bifocal contact lens and still wish to avoid wearing spectacles. As with bifocal contacts, the brain must choose between "competing" images, which can lead to compromised near as well as distant vision. Also, since the two eyes are not receiving the same prescription for near or distant at the same time, there is a decrease in depth perception. This potential problem also increases as the bifocal power increases.

Nevertheless, monovision enjoys probably the highest level of success in fitting patients who require a bifocal. Studies have shown that the success rate runs between 70 and 80%. This success rate is generally attributed to better overall vision (as compared to bifocal contacts, for example) and less fitting time involved. In my experience, I would agree with this assessment.

Modified Monovision

Modified monovision, also referred to as enhanced monovision, entails emphasizing distance correction for one eye - typically the dominant eye - and near correction for in the other eye. Bifocal lenses may be used in both or only one eye, depending on the situation. This works best for those patient's who want or need better distance vision than what is sometimes achievable with bifocal contacts, but also wants some near correction in the contacts. This allows those patients to continue avoiding spectacles.

I would estimate that about 40% of my patients who successfully wear bifocal contacts do so with the modified monovision option - at least part of the time.

Distance Vision Contacts with Reading Glasses

This method of wearing contacts involves the use of distance only contacts for both eyes with the use of reading glasses (also called "readers" or "magnifiers") over the contacts for near vision. This allows for sharp distance and near vision. There is no reduction in depth perception, as can happen with bifocal contact lens options.

This method of wearing contacts probably yields the highest level of success for those patients who need a bifocal. However, as you may have guessed, many do not prefer this method as glasses are still required at least part time.

Nevertheless, I generally advise this mode of wear for those patients who spend a lot of time in front of a computer, or doing anything for long periods of time at near.

Last But Not Least...

Bifocal contact lenses involve many of the same compromises in vision that spectacle bifocals have. However, being informed and having realistic expectations can only help if you do decide to try these lenses.

Most of the bifocal contact lens modalities discussed are available for patients to try in the prescribing doctor's office before actually buying any contacts. There is no cost other than the professional fees. This is typically the case for disposable and planned replacement contacts.

For non disposable contacts, the patient typically would be required to pay up front for both the contacts (or apply any insurance benefit), and the professional fees. However, it has been my experience that in the latter case, if a patient is unable to successfully wear the prescribed contacts, most offices will refund what the patient paid for the contacts, but not the professional fees. What this means to the patient is that if he/she ever considered trying bifocal contacts, they can do so with minimal financial risk.

This "minimal risk" environment applies not only to bifocal contacts, but to just about any contact lens out there. Of course, it is advisable to discuss your doctor's office policies before getting your eye exam and contact lens fitting.

Conductive Keratoplasty is a procedure whereby radio waves are introduced into the peripheral cornea in an attempt to steepen the corneal curve. This will increase the power of the cornea effectively making that eye nearsighted. In doing so, the eye will be able to read things up close more easily. This is accomplished because the radio waves emit energy that is absorbed by the surrounding tissue. The protein in the tissue then contracts pulling the surrounding areas inward. When done in a specific, calculated fashion the cornea changes shape to get the desired result.

This procedure is performed on individuals that see well in the distance, but do not want to wear reading glasses. When one eye sees near and the other distance, that is called Monovision. It used to be done a lot with contact lenses until multifocal contacts took over as a better alternative. The problem with employing mono vision is that one eye is always blurry. If looking far then the near eye is out of focus, and the opposite applies when reading up close. This new visual environment takes time to get used to, and some folks never adjust to it. The success rate depends on what your visual demand is, and what one's personality is. For example, I am way to neurotic to get used to it. A smudge on my reading glasses upsets me. I would be a terrible candidate for this surgery. On the other hand my business partner is always happy with everything, and would therefore be a great candidate. That is how he has gotten along with me for 14 years! So the first thing one needs to determine is what the expectations are and how you as a person deals with change.

The next consideration is what the uncorrected distance vision is. The best candidate is one who has no distance prescription at all. I have found that the 2 biggest factors that determine success with this procedure is.

1) realistic expectation

2) good distance uncorrected vision.

The first seems silly, but actually is the most important. If one expects to be perfect all the time with out any sacrifice then they should not have the surgery. The fact is that there will be poor binocular vision and thus bad depth perception. The will affect the tennis and golf game as well as judging distance when driving. Glare will also result when driving at night. I have had patients that were happy as clams despite less then perfect vision and the side effects that I mentioned because they expected as much. Others saw great and had very few side effects,but complained bitterly since they wanted perfection.

Distance vision plays a big role in success. If the non operative eye is farsighted the success rate goes down significantly. That eye will see blurrier after surgery, and will try to focus which will make the distance vision even worse. This accommodation with make the near vision worse since eyes focus together and will move the focal point in closer then the person wants to read. Therefore, only those individuals that have NO distance prescription at all should have CK.

I am fortunate to work with some of the best eye surgeons in the US and all these factors are carefully evaluated prior to making a decision. As they say," go into surgery with both eyes open."

Presbyopia, which literally means "old eyes," is a normal and expected consequence of the aging process, which results in the inability of the eyes to focus at all distances, due to the slow degeneration of your eye muscles. Usually you will first notice the effects of presbyopia when fine print starts to blur and you find yourself hold reading material farther and farther from your face.

This usually begins having an effect when you're between the ages of forty and fifty, and it continues to worsen until you reach about age sixty-five. An estimated 90 million baby boomers in America either have presbyopia or will develop the condition in the next 10 years, according to an April 2004 report by Refractec Inc.

Monovision LASIK surgery treats presbyopia by correcting one eye for long distance vision and the other eye for near vision. This procedure offers presbyopic and pre-presbyopic patients the ability to retain near and distance vision after surgery with little or no reliance on glasses or contact lenses. If you are over 50 and you choose to have traditional, rather than M-LASIK, you'll probably still need reading glasses after surgery. The concept of using one eye for close vision and one for distance is not new. It dates back as far as 1720, when Baron Philip Von Stosch invented the monocle. In more modern times, using different eyes for different vision has been done successfully for several decades, using contact lenses. Monovision as a form of LASIK surgery is the most recent development in presbyopia treatment, taking advantage of the fact that each of us has a dominant eye, much as we have a dominant hand.

Having radically different vision in each eye can take some getting used to. We are used to using both our eyes to see any object from two slightly different angles, which provides us with our depth perception. When your eyes are corrected for different distances, you'll be seeing almost all objects clearly through only one eye or the other. It is surprising how many people adapt readily and happily to this vision option, but it's not for everybody. Some people dislike its effect, particularly those whose work requires extremely precise near or far vision, such as engineers or police officers. For most people, the brain eventually adjusts to the difference in perception between the two eyes, but the period of adjustment is harder on some than on others. Certain aspects of sight that particularly require both eyes to work well together, such as night vision and depth perception, will never be perfect. Therefore, after monovision LASIK, you may want to own a pair of glasses that provide full distance vision correction (in both eyes).

Because not everyone can adjust to this new way of seeing, many doctors recommend you wear special monovision contact lenses for at least a week before committing to surgery. Monovision LASIK is a permanent operation to the cornea, and you want to be sure it will work for you before you commit to it.

Monovision LASIK was performed off-label for many years, meaning that it had not received official FDA approval as an approach to correcting presbyopia. However, this changed on July 12, 2007, when the FDA officially approved the surgery as a treatment for presbyopia. While this is an ambitious type of laser eye surgery, requiring careful patient selection and counseling, Monovision LASIK can offer excellent visual outcomes for both distance and close vision, and may be especially attractive to those hoping to never have to wear granny glasses!

The basic definition of monovision is the adjustment of one eye for near vision and of the other for distance vision. This means that each eye is operating separately instead of working together. If you were to choose monovision, your dominant eye, or the one that would be used to focus on a camera, would become the distance eye and the other would be used for near vision.

How Monovision is Achieved

The corrections used to create monovision can be done:

· Surgically with laser vision correction

· With IOLs (intraocular lenses)

· Traditionally with something like contact lenses

In most cases, your ophthalmologist may recommend trying contact lenses with monovision to see how you adapt to it before choosing permanent monovision through LASIK surgery. If monovision is created using laser vision correction and is not well tolerated, it may be reversed by having LASIK treatment on the other eye to make them the same.

How Monovision Works

Even though monovision may sound strange because we are used to our eyes working together, it can have its advantages. Monovision works because the brain chooses whichever image is appropriate for the task at hand, and ignores or filters out the blurry image from the other eye. This method is one type of vision known as simultaneous vision. For example,

· If you are reading and need near vision, the far vision image will be filtered out

· If you are driving and need far vision, the near vision image will be filtered out
Most people can easily adjust to monovision in time, but some people have difficulty with it.

Side Effects

There are some reported side effects of monovision, such as:

· Loss of sharpness,

· Decrease in depth perception

· Blurred near vision.
People who require very sharp vision for a hobby or occupation may not be pleased with monovision results. Monovision may require people to give up a small amount of distance vision to gain close up vision. There are also reports of seeing shadows when attempting to read small print. To correct some of these problems, people with monovision may need prescription glasses for things such as night driving.

However, the cost of monovision is lower than some other options like bifocal or multifocal implantable lenses.

Monovision may be the solution you are looking for if you want to preserve both near vision and distance vision, especially if you are over age 40-45. This is when presbyopia creeps up on us. Presbyopia is stiffening of the lens so that it can’t change its curvature so readily in order to accommodate itself to near vision. Reading glasses become necessary.

As with other vision correction solutions, you should discuss monovision thoroughly with your ophthalmologist to determine whether or not you would benefit from it. Dr. Jonathan Davidorf in West Hills, California offers more information [http://www.davidorf.com/vc_monovision.html] about monovision on his website.

Presbyopia

The lens, behind the iris, is normally adjusted by little muscles, which make it more curved or more flat, depending on how far away the object is that we're looking at. But with age, the lens becomes more stiff and harder to adjust; and the little muscles become a bit weaker.
So when we look at the print in our book, our lenses can't adjust properly, and stay set for looking at the tree at the back fence, and the print appears blurry.
That's where bi-focals, whether glasses or contact lenses, are useful, because they correct for close-up vision while correcting differently for far vision, or not correcting it at all.
Disadvantages of glasses

· They're so easily misplaced

· They have to be modified periodically as we age and our vision changes

· If you work in a job where you change focus often, such as teaching, sales, performing arts or public speaking, glasses can be very inconvenient and annoying

One eye on the horizon

The idea of monovision is to correct one eye for the distance vision and the other for close-up vision. In cases where distance vision needs no correcting, just the near-vision eye would be corrected.

Eye doctors started doing this with contact lenses. They made one lens to correct distance vision and the other to correct near vision. When LASIK surgery came along in the late 1990s, some people chose to have one eye corrected for distance and the other for close-up work.
This means that the two eyes don't work together any more. As you can imagine, this takes some getting used to, but it can be done.

An upside down world

A related experiment was done in the late nineteenth century by George Stratton. He wore special glasses which turned everything upside down, so that he saw the floor where the ceiling would normally be, and vice versa, and all objects correspondingly upside down.
He found that it only took about 3 days to adjust, so that things looked normal again. In other words, things didn't look upside down, but looked just as they normally do.
Then he took the glasses off and found everything looked upside down again. So again it took him a few days to re-learn and restore his normal vision.

Our brains can learn

With monovision, one eye is the distance eye and the other is the reading eye. We can learn to automatically use just one eye, the appropriate one for what is being focused on.
The adjustment period is several weeks. Most people who have it done are pleased with the result. Now they can see near and far without any contacts or glasses.
It's a good idea to try monovision with contact lenses first, to see how well you can adjust to it, and many people do this.
Disadvantages of monovision

· A slight loss of depth of perception

· A slight loss of peripheral vision

· If you need to see extra clearly at certain times, such as for night driving or long sessions with reading or computer work, you might want some reading glasses for those occasions, but will not need them for routine tasks

Advantages of monovision

· You'll need no glasses or contact lenses most of the time, perhaps ever

· You can legally drive without any vision correction

· The cost is lower than that of LASIK or other laser procedures

· It can be undone

If you have it done and decide you don't like it, you can have it undone, and your "near" eye corrected for distance. Then your 2 eyes will be working together again but you'll need to wear reading glasses.

If you wear bifocals or reading glasses, you might like to consider the option of dispensing with them and instead, using your brain's adaptive power to learn monovision. Some LASIK centers give little information about monovision. Some take time with you to explain how it works and answer your questions.

If you have it done and then change your mind about it, some will follow up with you and correct your near eye for distance vision at no charge, so that you can revert to using your reading glasses.