Laser Blended Monovision
Normal Vision enables you to see near and distant objects in similar sharp focus due to the mechanism of accomodation. This is achieved by the natural lensThe lens fulfils the same role as the lens in a camera. It handles about one-third of the focusing power of the eye and is critical for good vision.See Info on Eyes – Anatomy. in the eye that can adjust its focus on close-up as well as distant objects. While you age, however, the natural lens in your eye gradually loses its elasticity and at the age of around 45 years you start to develop difficulty to focus near. near visionNear vision is the ability to clearly focus on close-up opjects and fine print. See Other Options – Options for Refractive Correction. continues to deteriorate as you grow older and people often refer to this phenomenon as “their arms that are getting too short”, whereas it is actually their focus that becomes longer! This condition is known as presbyopiaPresbyopia is an age-related condition. As we age, the natural lenses in our eyes gradually become inelastic and lose their ability to focus on nearby objects and fine print. From the age of 40 it becomes increasingly noticeable and people often jokingly complain that their 'arms are getting too short'. See Info on Eyes – Optics and Refractive Errors - Presbyopia..
The most common treatment for presbyopia is reading glasses, which enable you to see close-up objects, but have to be removed for distant vision. Alternatively you may wear bifocal or multifocal lenses in your spectacles.
There is, however, an alternative solution to this problem. Just like the dominant hand of most individuals, every person also has a dominant and non-dominant eye. It is possible to use this physiological phenomenon to one’s advantage by using glasses, contact lenses or laser to correct the dominant eye for distance vision and the non-dominant eye for close-up vision. The brain then chooses the respective eye, depending on the distance of the object on which you focus. For those that are able to make this adjustment, it is possible to see close-up as well as distant objects in focus without the need for reading glasses. This visual arrangement is called monovisionMonovision is a term used to describe the situation where one eye is corrected by means of contact lenses or laser for near vision, while the other is corrected for distance vision in presbyopic individuals. It enables the patient to be less dependent on spectacles or contact lenses and applies to near and distance vision. See Near Vision – Laser Blended Monovision..
Monovision therefore occurs when you use the non-dominant eye for close-up vision and switches to the dominant eye for distance vision. The brain has to merge the two separate images into one, which may be hard for some people. Scientific studies show that approximately 60% of the normal population can successfully achieve this to produce binocular functional vision at near and far.
Even if you succeed to adapt to Monovision, the brain may need some time to fulfill these new demands. People that can adjust to this situation are generally very happy, since they are able to see at near and far despite their presbyopia.
Those that manage to tolerate the difference between the two eyes, are often left with a “gap” in the intermediate range. It is known as the “Blur Zone”, as illustrated on the left. It may also cause other side effects, like reduced contrast sensitivity and reduced binocular vision (stereopsis).
Before this method of correction is attempted with laser, a trial period with contact lenses is mandatory to determine whether this type of correction will work. Conventional Monovision is at best a compromise which, for some people, does not work well.
Laser Blended Monovision is a more recent development, which provides a more permanent and longer term solution to presbyopia. In contrast to conventional Monovision, this technique combines the simplicity and accuracy of laser refractive surgery with an increased depth of field. This is achieved by a modification of the asphericity of the corneaThe cornea is the clear, transparent 'front window' of the eye through which light enters the eye. It handles about two-thirds of the focusing power of the eye and is critical for good vision. See Info on Eyes – Anatomy. in the dominant as well as the non-dominant eye.
The normal Monovision routine is followed similar to Monovision with contact lenses, but due to the change in asphericity, the intermediate vision also improves. The result is that the patient experiences vision in focus at all distances – not only at near and at distance – when using both eyes in tandem.
The intermediate area is known as the “Blend Zone”, as illustrated on the left.