Other Types Of Vision Correction Procedures
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1. Refractive Lens Exchange
This procedure is recommended to correct the spectacle power in people over the age of 40 years. After the age of 40 years, the natural lens of the eye becomes hard and non-flexible and therefore loses its ability to change focus from distance to reading.
An eye is like a camera with a lens focusing light on the retina. Glasses are required if the image is out of focus. In RLE the natural lens is replaced by an artificial lens of suitable power to bring the image to focus on the retina without the need of glasses.
A simple way to understand is that the natural lens of the eye has the power of +21 Diopters. If a person has a spectacle power of -8 Diopters, then by exchanging the natural lens with an artificial lens of the power of +13, the spectacle power of -8 Diopters would stand corrected. However, practically calculations are not this simple. Ultrasound, biometry or costly optical biometers like the Lenstar have to be used to accurately determine the power of a lens which is to be implanted in the eye.
Two types of lenses can be used for this correction:
I) Monofocal Lens
It is a single power lens and the most popular one used in this category at our centre is the Acrysof IQ Lens from Alcon (USA).
This lens would enable the person to see clearly without glasses. Since this lens is a hard, non-flexible artificial lens, it would not change its power to focus for near distances, therefore for reading purposes, a spectacle power of approx. +2.5 is required.
Since an average person’s activity involves 95% of distant viewing and only 5% of near viewing, a person tends to be very comfortable from this newly formed freedom of glasses, and he does not mind using glasses occasionally for reading.
Ii) Multifocal Lens
For people desirous of having an excellent functional vision for distance and reading, the multifocal lens provides one such option. The most popular lens in this category used at our center is Acrisof Restor Multifocal lens from Alcon(USA).
The lens has rings of Fresnel prisms that divide the incoming light into two bundles, one focused for distance and one for near, thereby giving the person the advantage of seeing both for distance and near without glasses. However multi-focal lenses can sometimes be associated with halos and glare around light and slight loss of contrast. Most of the people can adapt to these problems over a period without losing out on the advantage of spectacle free distance and near vision.
The Restor Multi-Focal lens comes in three models:
- Model 1 comes with a near vision addition of +4 which is equivalent to +2.5 of near vision glasses.
- Model 2 comes with an addition of +3 which is equivalent to +1.75 of the near vision glasses.
- Model 3 comes with an addition of +2.5 which is equivalent to +1.25 of the near vision glasses.
The Patient may be offered these different combinations depending on his nature of work or personal requirements.
A +4 lens giving a spectacle equivalent of +2.5 is ideal for distance and reading but provides a poor quality of vision at an in-between distance which is also referred to as the computer screen distance from the eye.
The Model with a +2.5 addition equivalent to a spectacle power of +1.25 gives an excellent intermediary vision for computer work but fails if the person has high expectancy on reading without glasses.
The model 2 with a +3 addition is a compromise between the two lenses.
The model with +2.5 addition gives the least amount of halos and glares around lights and is ideal for people who want to be spectacle-free for routine indoor and outdoor activities and computer work and are willing to use a little spectacle correction for fine-tuning.
Presbyopia or decrease in near vision with age. In a young individual, the natural lens of the eye is soft and flexible and works like an auto-focus lens. By contraction of the internal eye muscles, it can change its power from a distance to near.
Around the age of 45, the natural lens of the eye undergoes age changes and tends to become hard and non-flexible. Even with contraction of internal eye muscles, it is unable to change its power from a distance to near therefore additional spectacle power is required for reading purposes.
In the elderly, the eye requires a distance and a near spectacle power. The laser can correct only one power either for distance or for near. In mono-vision, one eye is corrected fully to focus it for distance, and other, partially for near. Thus with both eyes open, the person can do most of his routine activities without glasses and only for very fine work does a person need glasses.
3. Corneal Inlays
Lots of research and innovations are in progress to overcome near vision handicap. One of the recent innovations is in the form of corneal inlays.
By placing inlays in the cornea, the near vision is enhanced, without losing the advantage of distance vision without glasses.
There are two popular models of corneal inlays:
I) Raindrop Inlays
Principle – Raindrop Corneal Inlay is a 2mm implant which is just 30 microns thick in the center. It is made of a hydrogel material which is highly biocompatible material. It is implanted within the deeper layers of the cornea, in the center of the line of sight. By making the central 2mm of the cornea steep, it enhances the capability of a person to see near vision objects without any significant loss of distant vision. The lens is implanted only in one eye which is called the non -dominant eye. It is usually the left eye in right-handed people. Thus with both eyes open, the person can now have a comfortable vision for distance and near without glasses.
A Femtosecond laser like the FS200 is a must to create the plane in the cornea to implant this inlay.
Ii) Kamra Inlays
Principle – It increases the depth of field using the laws of small-aperture optics (an extension of pinhole) to restore near and intermediate visual acuity without significantly affecting distance vision.
A small 5-micron thick button of 3.8 mm diameter with a central hole of 1.6 mm is placed in the center of the cornea in one eye, usually, the left eye which is the non-dominating eye. The 1.6 mm pinhole gives an additional advantage of near vision.
In all of the above treatments, technology and surgeon’s skills unite to give you the best-desired result. However, mild variations can always be expected.
Intacs is the face of modern technology for Refractive Correction. It is useful in low myopia -1.0D to -3.0D and in case of keratoconus, however, in low myopia the choice of refractive correction is LASIK.
In Keratoconus, Intacs have proven value by centering the cone, reducing the cylinder power and improving the quality of vision (by reducing aberration at the level of the cornea).
Patient of Keratoconus can undergo Intacs with or without C3R procedure, but it is preferable to do both the procedures at the same sitting. There may or may not be a small amount of residual power after Intacs which can be corrected by wearing specs or contact lenses. Higher residual powers may be corrected by ICL. The quality of vision for Keratoconus patient after Intacs is much better ever after wearing specs.