Presbyopia

 



Q1. What is presbyopia? When does it occur?
While presbyopia usually starts at the age of 38, most patients may not be aware of it until 45 and need to wear reading glasses. When we look at a near object, the image is focused behind the retina. And to focus the image on the retina, the lens will “auto-focus” and become thicker, thus increasing its refractive power. When we see a distinct object, the lens will become thinner and focuses the image on the retina.
 
Presbyopia develops, when the lens hardens and becomes less flexible, reducing the “auto-focus” power. The lens stays thin no matter where the image falls, i.e. in front of or behind the retina. Use of reading glasses is thus required to increase the refractive power, so that the image is focused more to the front.
 
An eye that cannot “auto-focus” is no different from a defective camera. It can only take pictures of distant but not near objects. It cannot function properly without new lens.
 
Q2. Can refractive surgery cure presbyopia?
Refractive surgery can reduce presbyopia. It also works for short-sightedness, long-sightedness or astigmatism. The surgery will reduce the myopia in one eye to 0 diopter, and adjust the other eye to myopia nearly -2.00 diopters for near vision. For long-sighted patients, the surgery will induce myopia of -2.00 diopters in one eye for near vision, while the other eye is designated for seeing distant objects. The same outcome can be achieved by refractive surgery for short-sightedness, long-sightedness or astigmatism.
 
Q3. What is Laser Blended Vision for presbyopia? What are its advantages?
Like cataract surgery, refractive surgery achieves distant and near vision by reducing the myopia in one eye to 0 diopter and keeping or adding -2.00 diopters of myopia in the other. With one eye designated for distant vision and the other for near vision, the patients can see things far and near. However, the intermediate vision may be less satisfactory.
 
A new “Laser Blended Vision” is now adopted in refractive surgery or cataract surgery. In refractive surgery, Laser Blended Vision can produce one eye mostly for distant and intermediate vision and the other for intermediate and near vision. In laser surgery, part of the cornea is flattened with a “small hill” in its centre that retains some myopia. For seeing distant objects, the pupil will dilate, and the periphery of the cornea with no myopia is used to see distant objects. When it comes to seeing near objects, the pupil will constrict using the region with remaining myopia. The periphery of the cornea is 0 diopter while it is -1.00 diopter in the centre. The pupil will constrict when we see near objects, and region with -1.00 diopter can be used for intermediate and near vision.
 
The other eye may retain -1.5 diopters in the periphery of the cornea for computer use, and -2.0 diopters in the “small hill” for near vision. Therefore you can have one eye for distant and intermediate vision, and the other for intermediate and near vision.
 
Thanks to Blended Vision, a full range of visual clarity can be achieved with one eye being corrected for near and intermediate vision, and the other for intermediate and distant vision. What’s more is that the eye designated for distant vision still has some near vision, and the other stays at -1.5 diopters and is good enough for seeing distant objects. Instead of merely creating one eye for distant vision and the other for near vision, Blended Vision can also achieve intermediate vision and provide a full range of visual acuity in distant, intermediate and near vision. 
 
Q4. What are the advantages of treating presbyopia with IOL exchange?
While Laser Blended Vision can correct presbyopia, it only applies to those with mild long-or short-sightedness and achieves no more than what Blended Vision can offer. IOL exchange is different. Like cataract surgery, one’s lens can be replaced in IOL exchange with a trifocal lens to achieve distant, intermediate and near vision. It is better than laser surgery in terms of visual acuity and convenience.
 
Q5. What types of IOL are available?
Like cataract surgery, IOL exchange is performed with a micro incision on the eyeball. The lens which is used to “auto-focus” looks like a grape. A small incision is made on the anterior capsule of the lens, and through this hole the lens is removed and replaced by an IOL. Conventional artificial lenses are monofocal. With only one focus, monofocal lenses have been in use in MonoVision, which corrects vision with one eye at 0 diopter for distant vision and the other at -2.0 diopters for near vision. The downside is poor intermediate vision, with which one may find it difficult to use computers, cook, play mahjong, paint, etc. Therefore for achieving good intermediate vision, multifocal lenses such as bifocal and trifocal lens and Extended Depth of Focus (EDOF) lens are needed. 
 
A bifocal lens can be used to achieve distant and near vision, or distant and intermediate vision. It can be done with one eye for distant and intermediate vision and the other with low myopia for intermediate and distant vision to achieve full visual acuity at all distances. With more diffractive rings in its design, a trifocal lens can also achieve distant, intermediate and near vision. While both eyes can see objects at far, intermediate and close distances with trifocal lenses, it comes at a price: the more the rings are on the lens, the more halo appears around outdoor lights at night. One may even see double image, become sensitive to light or have a little hazy vision.   
 
Convenient for use, trifocal lenses can achieve distant, intermediate and near vision. Nearly 95% of patients no longer need glasses after surgery. For those who need to drive or engage in outdoor activities like golf, tennis and football at night, EDOF (Extended Depth of Field) is another option. While EDOF can achieve the same outcome as Laser Blended Vision with fewer rings in its design, it falls short of achieving full visual acuity. EDOF allows one to see clearly at intermediate to far distances but not close objects. In this case, an eye is designated for distant and intermediate vision, and the other stays at -1.5 diopters for intermediate and near vision. While EDOF is not as good as trifocal lens in terms of visual correction, its fewer rings mean less halo at night and a lower chance of double image. The chance to see double image after surgery is minimal, even less than 1/1000, but there are still some risks. And it is less likely with EDOF. Instead of seeing things as if through a soft lens, patients using EDOF in Blended Vision are less likely to have hazy vision. There is also a bifocal and EDOF lens, whose upper part is for distant vision and the lower for the close distance suitable for using a mobile phone. Also an EDOF, it causes no hazy vision or halo. 
 
There are many different types of lens, but the more functions one has, the more visual problems it may cause, e.g. blurred images, halo or star patterns around light sources, especially in a dim environment. While hazy vision may occur in both light and dim environments, it is less likely with EDOF or bifocal lens. Good distant, intermediate and near vision can be achieved with a trifocal lens, but often not without the same problems. IOL exchange has one advantage: you can change the lens whenever you are not satisfied with the outcome of the existing one.

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