LASIK/ PRK/ ICL
How the Eyes Work & See
The eye can be likened to a camera. As light passes through the cornea and lens it is bent and transposed / focused onto the eye’s film – the retina. The film is then ‘developed’ by the brain, becoming the image that we see and interpret.
As light enters the eye it first passes through the cornea – the clear ‘window’ to the eye. Because the cornea is curved, the light rays bend (refract). Light then passes through the pupil to the lens. The iris – the colored portion of the eye – controls the amount of light that enters the eye with muscles that cause the pupil to contract if there is too much light or to dilate if there is too little light. When light hits the curved surface of the lens it is refracted, or bent even more, so that it focuses properly on the retina. The retina then turns the light into electrical energy, which passes through the optic nerve to the brain stem, and into the occipital lobe where it is converted into an image. To summarize:
• Cornea – clear surface of the eye. Light rays refract as they pass through to the pupil.
• Iris – colored portion of the eye. The iris controls the amount of light that passes through the pupil.
• Pupil – an open space in the center of the iris. Light passes through the pupil to the lens.
• Lens – refracts light to focus it properly on the retina.
• Retina – converts light rays into electrical energy. This electrical energy is passed to the optic nerve.
• Optic Nerve – serves as a pathway to the brain stem, which forwards electrical energy to the occipital lobe.
• Occipital Lobe – electrical energy is converted into an image.
• This process works perfectly in people with 20/20 vision. Imperfect vision occurs when the shape of the eye is irregular or when the eyeball length is above or below average, so that the light rays do not focus directly on the retina – these imperfections are collectively known as refractive errors.
Many people rely on glasses and contacts to correct their vision, but some find these methods inconvenient, uncomfortable or unattractive.
Refractive eye surgery is a general term for surgical procedures that can improve or correct the eye’s focus by permanently changing the shape of the cornea. The cornea is the clear, front surface of the eye which bends or refracts light rays as they enter the eye.
For you to see clearly, light rays must be focused by the cornea and lens to fall precisely on the retina, a layer of light sensing cells that lines the back of the eye.
The retina converts the light rays into impulses that are sent through the optic nerve to the brain, which interprets them as images.
This process is very similar to the way a camera takes a picture. The cornea and lens in your eye act as the camera lens.
The retina is similar to the film. If the image is not focused properly, the retina or film receives a blurry image. This condition in the human eye is known as a refractive error.
There are three types of refractive errors that can be corrected or reduced by refractive surgery.
Myopia or nearsightedness / shortsightedness is a refractive error that causes poor distance vision. If your eye is too long, or your cornea has too much focusing power, images focus short of or in front the retina.
If you have myopia, light rays have past the correct focal point by the time they reach the retina. The retina then sends this “over-focused,” blurry image to the brain. This condition affects over 25% of all people in the United States, and is rising all over the world.
Hyperopia or farsightedness / long-sightedness is the opposite of myopia. Distant objects are clear and close up objects appear blurry. This condition is a result of a eye that is too short or a cornea that lacks the necessary refractive power to focus images on the retina.
If you have hyperopia, images focus on a point beyond the retina. This unfocused or “under-focused” image captured by the retina is then sent to the brain and processed as an unclear picture.
Astigmatism is a condition which blurs and distorts both distant and near objects. A normal cornea is round like a soccer ball. With Astigmatism your cornea is shaped more like the back of a spoon, curved more in one direction than in another. Light rays have more than one focal point on the Line of sight.
Correcting Your Vision With Glasses and Contacts
Glasses and contact lenses correct refractive errors by adding or subtracting focusing power to your cornea and lens. The power needed to focus images directly on your retina is measured in diopters. This measurement is also known as your eyeglass prescription.
If you have myopia, your Glasses and contacts need to subtract power from your eye’s natural focus and allow light rays to focus further back onto the retina.
In myopia, your prescription will be negative, such as -4.25 diopters
If you have hyperopia, Glasses and contacts add focusing power to your eye, causing light rays to bend more as they enter the eye. This process moves the focal point back onto the retina, allowing for clear vision. For hyperopia, your prescription will be positive, for example, +4.25 diopters.
If you have astigmatism, the shape of the glasses’ lens compensates for the uneven corneal curves and focuses the light rays to a single point on the retina.
What is LASIK / Refractive Surgery?
The goal of this Web site is to provide objective information to the public about LASIK & Refractive Surgery. See other sections of this site to learn about what you should know before surgery, what will happen during the surgery, and what you should expect after surgery. There is a glossary of terms and a checklist of issues for you to consider, practices to follow, and questions to ask your doctor before undergoing LASIK surgery.
Learning About LASIK
LASIK is a surgical procedure intended to reduce a person’s dependency on glasses or contact lenses.
LASIK stands for Laser-Assisted In-Situ Keratomileusis, and is a procedure that permanently changes the shape of the cornea – the clear covering of the front of the eye – using an excimer laser.
A device called a microkeratome, is used to form a flap in the outer cornea layer. The flap is folded back on a hinge, revealing the stroma – the middle section of the cornea.
Computer-controlled Laser Pulses vaporize / sculpts a calculated thin layer off this stroma and the flap is then replaced to cover the ‘lasered’ area and heal.
Other types of refractive surgery procedures:
Radial Keratotomy (or RK) and Photorefractive Keratectomy (or PRK) are other refractive surgeries used to reshape the cornea.
In RK, a very sharp knife is used to cut slits in the cornea to change its shape.
PRK was the first Laser surgical procedure developed to reshape the cornea, by sculpting it with a laser since the mid to late 1980’s.
LASIK was developed later using the same type of laser.
The major difference between the two surgeries is the way that the stroma, the middle layer of the cornea, is exposed before it is vaporized with the laser.
In PRK, the top layer of the cornea, called the epithelium, is scraped away to expose the stromal layer underneath.
In LASIK, a flap is cut in the front stromal layer and the flap is folded back.
In Thermokeratoplasty a different type of Laser heat is used to reshape the cornea. This option is now rarely used.
Other refractive surgery methods include Intra-corneal ring segments (ICRS) that are inserted into the stroma to reshape the cornea, and Non-Surgical Customized Specialty contact lenses that temporarily reshape the cornea (orthokeratology).
What should you expect before, during, and after surgery?
This will vary from doctor to doctor and patient to patient. This section is a compilation of patient information developed by manufacturers and healthcare professionals, but cannot replace the dialogue you should have with your doctor. Read this information carefully and with the checklist, discuss your expectations with your doctor.
If you decide to go ahead with LASIK surgery, you will need an initial or baseline evaluation by your eye doctor to determine if you are a good candidate. This is what you need to know to prepare for the exam and what you should expect:
If you wear contact lenses, it is a good idea to stop wearing them several weeks before your baseline evaluation and switch to wearing your glasses full-time.
Contact lenses change / warp the shape of your cornea for up to several weeks after you have stopped using them, depending on the type of contact lenses you wear.
Not leaving your contact lenses out long enough for your cornea to assume its natural shape before surgery can have negative consequences. These can include inaccurate measurements and a poor surgical plan, resulting in poor vision after surgery.
These measurements, which determine how much corneal tissue to remove, may need to be repeated at least a week after your initial evaluation and before surgery to make sure they have not changed, especially if you wear RGP or hard lenses.
If you wear:
· soft contact lenses, you should stop wearing them for 2 weeks before your initial evaluation.
· toric soft lenses or rigid gas permeable (RGP) lenses, you should stop wearing them for at least 3 weeks or more before your initial evaluation.
· hard lenses, you should stop wearing them for at least 4 to 8 weeks before your initial evaluation – In some cases even 12 weeks or 3 months.
You should tell your doctor:
· about your past and present medical and eye conditions
· about all the medications you are taking, including over-the-counter medications and any medications you may be allergic to
Your doctor should perform a thorough eye exam and discuss:
· whether you are a good candidate
· what the risks, benefits, and alternatives of the surgery are
· what you should expect before, during, and after surgery
· what your responsibilities will be before, during, and after surgery
You should have the opportunity to ask your doctor questions during this discussion. Give yourself plenty of time to think about the risk/benefit discussion, to review any informational literature provided by your doctor, and to have any additional questions answered by your doctor before deciding to go through with surgery and before signing the informed consent form.
You should not feel pressured by your doctor, family, friends, or anyone else to make a decision about having surgery. Carefully consider the pros and cons yourself.
The day before surgery, you should stop using creams, lotions, makeup & perfumes.
These products as well as debris along the eyelashes may increase the risk of infection during and after surgery.
Your doctor may ask you to scrub your eyelashes for a period before surgery to get rid of (makeup) residues and debris along the eye lashes.
Also before surgery, arrange for transportation to and from your surgery and your first follow-up visit. On the day of surgery, your doctor might give you some medicine to make you relax. This medicine impairs your ability to drive and your vision may be blurry. Even if you don’t drive make sure someone can bring you home after surgery.
The surgery should take less than 30 minutes. You will lie on your back in a reclining chair in an exam room containing the laser system. The laser system includes a large machine with a microscope attached to it and a computer control screen. Before the start of surgery, your doctor will have programmed the computer to vaporize a specified amount of tissue based on the measurements taken at your pre-op evaluations.
A numbing drop will be placed in your eye, the area around your eye will be cleaned, and an instrument called a lid speculum will be used to help keep your eyelids open.
A ring will be used to hold onto your eye and very high pressures will be applied to create measured suction onto the cornea. Your vision will dim while the suction ring is on, and you may feel the pressure and experience some discomfort during this part of the procedure. The microkeratome, is attached to the suction ring to create a flap in your cornea.
The microkeratome is removed and the suction ring is released. You will be able to see, but with fluctuating degrees of blurred vision during the rest of the procedure. The doctor will lift the flap and fold it back on its hinge, and dry the exposed tissue.
The laser will be positioned over your eye and you will be asked to stare at a light. This is not the laser used to remove tissue from the cornea. This light is to help you fixate by staring at a fixed object for about 60 seconds. (Remove), you may not be a good candidate for this surgery.
When your eye is in the correct position, your doctor will start the laser. At this point in the surgery, you may become aware of new sounds and smells.
The pulse of the laser makes a fast ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair.
A computer controls the amount of laser delivered to your eye. After the pulses of laser energy have vaporized the corneal tissue, the flap is put back into position.
A shield should be placed over your eye at the end of the procedure as protection, since no stitches are used to hold the flap in place. It is important for you to wear this shield as directed, to prevent you from rubbing your eye and putting pressure on your eye while you sleep, and to protect your eye from accidentally being hit or poked until the flap has healed.
Immediately after the procedure, your eye may feel burning, itching, or feel like there is something in it.
You may experience some discomfort, or in some cases, mild to moderate pain and your doctor may suggest you take a mild pain reliever. Both your eyes may tear or be watery.
Your vision will probably be hazy or blurry.
Your doctor may give you one or more types of eye drops to take at home to help prevent infection and/or inflammation. You may also be advised to use artificial tears to help lubricate the eye.
** Do not resume wearing a contact lens in the operated eye, even if your vision is blurry.
You will instinctively want to rub your eye, but don’t! Rubbing your eye could dislodge the flap, requiring further treatment.
You may experience sensitivity to light, glare, starbursts or haloes around lights, and the whites of your eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery.
You should plan on taking a few days off from work until these symptoms subside. You should contact your doctor immediately and not wait for your scheduled visit, if you experience severe pain, or if your vision or other symptoms get worse instead of better.
You should see your doctor within the first 24 hours after surgery and at the regular arranged intervals after that for at least the first six months.
At the first postoperative visit, your doctor will remove the eye shield, test your vision, and examine your eye.
You should wait one to three days following surgery before beginning any non-contact sports, depending on the amount of activity required, how you feel, and your doctor’s instructions.
To help prevent infection, you may need to wait for up to two weeks after surgery or until your doctor advises you before using lotions, creams, or make-up around the eye. Your doctor may advise you to continue cleaning your eyelashes for a period of time after surgery.
You should also avoid swimming and using hot tubs or whirlpools for 1-2 months.
Strenuous contact sports such as boxing, football, karate, etc. should not be attempted for at least twelve weeks after surgery. It is important to protect your eyes from anything that might get in them and from being hit or bumped to shift the flap.
During the first few months after surgery, your vision may fluctuate.
* It may take up to three to six months for your vision to stabilize after surgery.
* Glare, haloes, difficulty driving at night, and other visual symptoms may also persist during this stabilization period.
*If further correction or enhancement is necessary, you should wait until your eye measurements are consistent for two consecutive visits at least 3 months apart before re-operation.
* It is important to realize that although distance vision may improve after re-operation, it is possible that other visual symptoms such as glare or haloes might not improve.
* It is also important to note that no laser company has presented enough evidence for the FDA to make conclusions about the safety or effectiveness of enhancement surgery.
Contact your eye doctor immediately, if you develop any new, unusual or worsening symptoms at any point after surgery. Such symptoms could signal a problem that, if not treated early enough, may lead to significant loss or deterioration of vision.
What are the risks ?
Most patients are very pleased with the results of their refractive surgery. However, like any other medical procedure, there are risks involved. That’s why it is important for you to understand the limitations and possible complications of refractive surgery.
Before undergoing a refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so.
- You may be undertreated or overtreated. About 80-85% of patients achieve 20/20 vision without glasses or contacts.
You may require additional treatment, but additional treatment may not be possible. You may still need glasses or contact lenses after surgery. This may be true even if you only required a very weak prescription before surgery.
If you used reading glasses before surgery, you may still need reading glasses after surgery unless you opted for “Monovision”.
- Results are generally not as good in patients with very large amounts of astigmatism or very large refractive errors of any type.
You should discuss your expectations with your doctor and realize that you may still require minor glasses or contacts after the surgery.
- Results may not be long lasting. The level of improved vision you experience after surgery may be temporary, especially if you are farsighted or currently need reading glasses. **It is especially important for farsighted and Astigmatic individuals to have a cycloplegic refraction (a vision exam with lenses after dilating drops) as part of the screening process.
Patients whose manifest refraction (a vision exam before dilating drops) is very different from their cycloplegic refraction are more likely to have temporary results.
- Some patients lose Quality of vision. Some patients lose lines of vision on the vision chart that cannot be corrected with glasses, contact lenses, or surgery as a result of treatment. Refractive procedures may affect other aspects of vision, such as contrast sensitivity (the ability to see objects clearly against a similar background or in dim lighting conditions).
Some studies suggest that patients do not see as well in situations of low contrast, such as at night or in fog, after Refractive treatment as compared to Pre-op.
- Therefore, patients with low contrast sensitivity to begin with should rather not have a refractive surgery procedure.
It is important for you to know that not all eye centers test contrast sensitivity, and that when it is tested, it should be done in a dark room.
- Some patients may develop severe dry eye syndrome .As a result of surgery, your eye may not be able to produce enough tears to keep the eye surface moist and comfortable. This condition may be permanent. Intensive drop therapy and the use of plugs or other procedures may be required.
Additional Risks if you are Considering the Following:
Monovision is one clinical technique used to deal with the correction of presbyopia – the gradual loss of the ability of the eye to change focus for close-up tasks that progresses with age. The intent of monovision is for the presbyopic patient to use one eye for distance viewing and one eye for near viewing.
This practice was first applied to fit contact lens wearers and more recently to LASIK and other refractive surgeries. With contact lenses, a presbyopic patient has one eye fit with a contact lens to correct distance vision, and the other eye fit with a contact lens to correct near vision.
In the same way, with LASIK, a presbyopic patient has one eye operated on to correct the distance vision, and the other operated on to correct the near vision. In other words, the goal of the surgery is for one eye to have vision worse than 20/20, the commonly referred to goal for LASIK surgical correction of distance vision.
*Since one eye is corrected for distance viewing and the other eye is corrected for near viewing, the two eyes no longer work well together. This results in poorer quality vision and a decrease in depth perception.
These effects of monovision are most noticeable in low lighting conditions and when performing tasks requiring very sharp vision.
Therefore, you may need to wear glasses or contact lenses to fully correct both eyes for distance or near when performing visually demanding tasks, such as driving at night, operating dangerous equipment, or performing occupational tasks requiring very sharp close vision (e.g., reading small print for long periods of time).
Many patients cannot get used to having one eye blurred at all times. The difference between monovision with contact lenses and monovision with LASIK is that you can always take contact lenses out or have them changed (the treatment is reversible and adjustable) as opposed to LASIK, where the result of the surgery is not reversible or adjustable without enhancement.
Therefore, if you are considering monovision with LASIK, make sure you go through a trial period with contact lenses to see if you can tolerate monovision, before having the irreversible surgery performed on your eyes.
Just before this trial period starts, find out if you pass your state’s driver’s license requirements with monovision, or if you need supplemental glasses to drive.
In addition, you should consider how much your presbyopia is expected to increase in the future. Ask your doctor when you should expect the results of your monovision surgery to no longer be enough for you to see near-by objects clearly without the aid of glasses or contacts, or when a second surgery might be required to further correct your near vision.
- Bilateral Simultaneous Treatment
You may choose to have LASIK surgery on both eyes at the same time or to have surgery on one eye at a time.
Although the convenience of having surgery on both eyes on the same day is attractive, this practice is riskier than having two separate surgeries. The second eye may have a higher risk of developing an inflammation if surgery is done on the same day than if surgery is performed on separate days.
If a malfunction of the laser or microkeratome occurs causing a complication with the first eye, the second eye is more likely to also experience the same complication if the surgery is performed on the same day rather than on separate days.
If you decide to have one eye done at a time, you and your doctor will decide how long to wait before having surgery on the other eye. If both eyes are treated at the same time or before one eye has a chance to fully heal, you and your doctor do not have the advantage of being able to see how the first eye responds to surgery before the second eye is treated.
Another disadvantage to having surgery on both eyes at the same time is that the vision in both eyes may be blurred after surgery until the initial healing process is over, rather than being able to rely on clear vision in at least one eye at all times.