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Epi-LASIK
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Epi-LASIK is one of the ways of doing LASIK when you have been disqualified as a good candidate for standard LASIK. Ophthalmologists have developed several such procedures, so that vision correction can be offered to more people.
Many factors are considered when you are being evaluated for refractive surgery – that is, surgery to change the way your eyes bend light rays. All the LASIK procedures work by changing the cornea’s curvature. The cornea is the front clear part of the eye which lets light pass through it, through the pupil to the lens, and through the lens to the retina at the back of the eye. On the retina are light-sensitive cells which receive the images contained in the light rays. They pass them on to the brain via the optic nerve, and in that way, we can see things clearly and find names for them.
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The eye and light refraction
Light coming from far objects needs to be bend (refract) less than light coming from near objects.
• If you look at the center of your browser screen and imagine the angle of light coming into your eye’s small pupil from all four edges, you’ll see that those four lines must be somewhat bent inwards to get so close together than they can all pass through your eye’s pupil and converge at the back of your eye.
• Now, if you look at a distant object, let’s say a car parked outside the window, and imagine the light rays coming from the car’s outline, their angle is flatter as they converge to enter the pupil and focus on the retina.
Accommodation
The cornea, being curved and translucent, allows light through itself and bends the light rays according to its curvature. Behind it is the eye’s lens. While the cornea stays the same shape all the time, the lens does not. It becomes more convex (curvier) when you look at near objects and flatter when you look at that car outside the window. This ability to change curvature is called accommodation. It’s a fine-tuning of the cornea’s light refraction.
So clear vision depends on all light, regardless of where it comes from, focusing on the retina. But they only do that in a 20/20 eye.
• If you are nearsighted (myopic), they focus in front of the retina. That means that the information obtained by the retina’s special cells is not clear, and what you see isn’t clear.
• If you are farsighted (hyperopic), the light focuses behind the retina and again your vision is unclear.
• If you are astigmatic, you have an oval cornea instead of a round one. That means light focuses in two ways, again giving you blurry vision.
How Epi-LASIK works
Like all LASIK procedures, it uses a laser to vaporize tiny pieces of corneal tissue to change the cornea’s curvature. The first step in all LASIK procedures is to expose the corneal layer to be worked on, which is below the cornea’s surface (epithelium). The usual method is to make a corneal flap, bend it out of the way, do the laser work, then replace the flap. It will heal nicely by itself.
But some people have thinner corneas than average. So there is not enough corneal tissue to allow for the flap and the tissue vaporization, and still have enough to maintain the eye’s shape against its internal pressure. Eyes are filled with fluids which push outward and must be consistently contained.
So epi-LASIK creates a thinner flap. It uses a finer blade to cut the flap called a trephine (LASIK uses a microkeratome). Your eye surgeon does not lift the flap until he soaks it for about 30 seconds in a diluted alcohol solution. The alcohol weakens cell connections, making it easier to lift the thinner flap.
Then laser treatment is done the same way as for LASIK, and the flap is replaced. Being thinner, it gives less protection during healing, so bandage contact lenses are worn for a few days. Vision improvement is just as dramatic and gratifying as you get from LASIK.
Contact the Khanna Institute of LASIK and Refractive Surgery for more information about different LASIK options and to schedule your initial consultation.
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