Corrective Laser Eye Surgery For Presbyopia At The London Vision Clinic
Correction of refractive error should no longer be considered the only aim of refractive surgery. As almost any refractive error can now be corrected fully. The final refractive surgical frontier is the challenge of correcting presbyopia. Currently there are two main surgical approaches to correcting presbyopia, mono-vision and multifocality. The first attempt to create a multifocal cornea using an Excimer laser was by Meditech in 1991 using the MEL60 Excimer laser. A small superior zone was intended for near while the majority of the profile was intended for distance.
Dan Reinstein Discusses The Development Laser Eye Surgery Technology For Treating Presbyopia
Since then other multifocal ablation profiles have been used such as creating a central area for distance vision with a mid peripheral area for near vision. Or, steepening a central area for near vision leaving the mid-periphery for far vision. Multifocal and accommodative intraocular lenses have also been designed and are being used, but the underlying problem with any multifocal presbyopic correction is that the brain is not wired to interpret multiple images in the same eye. And so, there is often a very long neuro adaptation period required.
On the other hand, the brain has been naturally programmed for millions of years for binocular vision to suppress the blur from one eye or the other, which is why mono-vision is naturally tolerated by many patients. Here we present specialised MEL80 non-linear aspheric ablation profiles designed to increase the depth of field and implement it together with a new micro mono-vision protocol. In presbyopia the loss of accommodation means that the near vision in both eyes becomes blurred leaving the patient needing reading glasses. The ideal solution would be to be able to increase the depth of field of each eye, so that each eye could see clearly at distance intermediate and near. So far, the non-linear aspheric profiles have been shown to increase the depth of field but not enough to give the patient clear vision at all distances far to near.
In order to give the patient good reading vision the non-dominant eye is slightly shifted towards myopia. This results in one eye being clearly focussed for near vision, but only slightly blurred at distance, and the other eye being clearly focussed for distance vision, but only slightly blurred at near. The increased depth of field in each eye means that there is a region where the range of clear vision overlaps known as the blend zone. The result is that good binocular near, intermediate and distance vision can be achieved with a lower of degree of anisometropia than traditional mono-vision, which we refer to as micro mono-vision. Therefore, much less suppression is required and there is no disassociation between the eyes.
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Laser Blended Vision Compared To Traditional Mono-Vision
In traditional mono-vision the depth of field of each eye is comparatively smaller, meaning that the near eye needs to be more myopic for the patient to read comfortably and leaving a gap between the range of vision of the two eyes. This replaces the intermediate blend zone with a blur zone. This makes traditional mono-vision much less tolerated than Laser Blended Vision. Published reports found that traditional mono-vision was tolerated by about 60% of patients, whereas Laser Blended Vision where the relative blurring in each eye is reduced, has been found to be tolerated by about 97% of patients. The surgery itself is identical to a standard lasik procedure, so the risks are very low compared to producing surgical pseudophakia.
In summary, the use of non-linear aspheric profiles that increase the depth of field of each eye, enables the difference between eyes to be greatly reduced. Increasing tolerance, providing continuous good vision from near through intermediate to distance objects and all this using standard extra-ocular lasik surgery, optimising both patient satisfaction and surgical safety.
To learn more visit London Vision Clinic Laser Blended Vision pages.