How does the eye work?
The eye works by the light reflected on various objects around us to the eye. It receives light reflections by converting light impulses into images. To simplify this process light rays are focused by the cornea then the eye lens. The cornea is the main focusing part of the eye therefore; any slight change in the cornea could cause a refractive error such as myopia (or nearsightedness), astigmatism and hyperopia (or farsightedness).
But to explain how to see things, the healthy eye focuses light waves originating from various distances from the eye. The retina converts these light waves to nervous impulses and conveys them to the brain where an image is perceived. See picture (1)
The following refractive errors are the most common eye errors:
Myopia (nearsightedness): When the cornea is curved too much, or if the cornea of the eye sticks out more than usual, far objects will appear blurry because the light rays are focused in front of the retina instead of directly on it. See picture (2).
Hyperopia (farsightedness): When the cornea is less curved, or if the cornea of the eye sticks out less than the normal eye. In hyperopia, the light rays are focused on a point beyond the retina. See picture (3).
Astigmatism: is a condition in which the cornea is oval and curved more in one direction than in another. This causes light rays to have more than one focal point and focus on two separate areas of the retina, distorting the visual image. See picture (4).
Presbyopia: is a common type of vision disorder that occurs as you reach 40 years old. The eye is not able to focus light directly on to the retina due to the hardening of the natural lens. Presbyopia cannot be treated with Laser surgery. Laser treatment changes the shape of the cornea and as presbyopia is a condition which affects the lens of the eye, surgery to the cornea will not correct it.
How are refractive errors corrected?
1. Eye Glasses - this is the method chosen by most nearsighted people; it is the safest, the most accurate and possibly the least expensive.
2. Contact Lenses - if fitted and used properly, contact lenses are safe and effective for the correction of myopia. Hard or soft contact lenses give sharp vision with minimum complications.
3. Surgery - some people want a more permanent solution to refractive errors. You have to undergo some examinations so your doctor will be able to choose the proper surgery for you.
Excimer Laser is an ultra-violet light and an argon-fluoride gas that produce a "cool" laser to break the intra-molecular bonds in collagen molecules. The easiest way to imagine the laser surgery result is by imagining putting the corrective power in the front of the eye directly to be able to see clearly without using any of the vision correction methods such as eye glasses and contact lenses.
There are two procedures to correct vision by using Excimer Laser:
· Laser (PRK)
The unparalleled precision of the excimer laser makes it uniquely suited to the task of refractive corneal surgery. Each pulse of the laser removes 0.25 microns of tissue. Think of it as slicing 1/200 of a human hair.
This is the most common procedure among the laser vision corrections. This procedure is very effective and it is an outpatient procedure, so the patient doesn't need to stay at the surgery center overnight. Moreover, this procedure could be used to correct the different levels of refractive errors even the very poor ones. Lasik is considered to be one of the most common procedures which could be preformed in any health facilities in the world.
Although there is no perfect medical procedure, but the Excimer laser surgery gives an accurate and successful results.
Steps before the LASIK / LASER procedure (PRK):
Your eye doctor will perform eye examinations to determine if your eyes are healthy enough for the procedure, what kind of vision correction you need and how much laser ablation is required. Also, a corneal topographer usually is used; this device measures the curvature of your eye and creates a kind of "map" of your cornea. It is important to avoid wearing contact lenses for no less than two weeks before surgery.
Before surgery, the nurse will use topical sedation eye drops to sedate your eyes and prevent pain beforehand. The doctor will have you lie down, and then make sure your eye is positioned directly under the laser. (One eye is operated on at a time.) A kind of retainer is placed under your eyelids to keep them open - normally, this is not uncomfortable. The surgeon will use an ink marker to mark the cornea before the flap is created. The flap is then created by a microkeratome (computerized device). The device is securely attached to your cornea with a suction ring to prevent eye movements or loss of contact that could affect flap quality. During the procedure you won't actually see the creation of the flap, which is very thin. Afterwards, the surgeon uses a computer to adjust the excimer laser for reshaping the surface of the cornea accurately. See picture (5)
When this procedure is finished, the surgeon will return the corneal flap tightly then removes the retainer from your eyelids. In the next few days the corneal flap will heal and return to its normal shape.
This procedure takes 15-20 minutes for both eyes where focusing the laser in each eye will take less than one minute.
After the whole procedure is finished, you will rest for 15-20 minutes to make sure that everything is normal before leaving the hospital. During that time more eye drops will be administered into your eyes to maintain its moisturizing level. After surgery, it is important that you avoid rubbing your eye. Also, you need to wear sunglasses to protect your eyes from bright lights and winds, and use antibiotic eye drops to prevent your eyes from infections and inflammations.
You may feel that you need to rest for a few hours after discharge from the hospital. With LASIK surgery, most people's vision improves right away, but some find that their vision gradually improves in late evening. You may be able to go to work the next day, but many doctors advise a couple of days of rest instead.
A follow-up by your ophthalmologist is necessary to insure the healing of your eye. You should observe some restrictions for one week after the surgery and follow your doctor`s instructions to be able to resume all your daily activities.
Refractive errors correction by Laser (PRK):
Refractive errors correction by Laser (PRK) was one of the most common procedures but recently Lasik became more common because it could correct more severe refractive errors with short postoperative recovery period and less pain, and it can also limit infection and the central haze of the cornea.
The Laser (PRK) examinations are the same examinations done for patients undergoing Lasik surgery.
Laser (PRK) Surgery Steps:
The surgeon will prepare the eye for the procedure by removing the outer layers of corneal tissue to an exact length and depth with minimal disruption to the remaining eye tissue by using a cool laser ray which could be controlled by computer incorporated in the laser machine to guide removal of the exact amount of corneal tissue and leaving a smooth corneal surface.
This procedure takes approximately from 1 to 2 minutes and 15 minutes for preparation.
After the surgery, patients are usually given a course of antibiotic and anti-inflammatory eye drops. You probably will wear a special "bandage" contact lens during the healing process and it will be removed by the doctor in 3 or 5 days after surgery when the surface of the cornea is healed. The eye should be examined several of times to make sure that there is no infection. After the healing process the patients should use anti-inflammatory cortisone drop for three months under ophthalmologist direct supervision.
The following are guidelines for patients to have a refractive errors correction surgery:
1. Your age must be 18 years or older.
2. History of stable refraction for no less than one year.
3. No history of any corneal or retinal diseases including keratoconus.
4. Having a good health condition.
5. Women should make sure that you are not pregnant.
6. You should consult your doctor before undergoing the surgery.
The main goal of consulting your doctor is to determine if you are a good candidate for Lasik or / Laser (PRK) or not by undergoing some examinations. These examinations will help your doctor to choose which of these procedures is appropriate for you.
It is also important that your doctor explains to you the advantages and disadvantages of Lasik / Laser (PRK) procedures, and the expected results. In addition to explaining your role and the procedure's surrounding circumstances.
The advanced technology used in Refractive eye surgeries is developing. Refractive errors correction surgeries using laser are used for severe cases only and are not appropriate for everyone and some patients (patients with ocular diseases which includes the cornea or the retina). One type of surgery may be more suitable for one person than another.
ANSWERS TO QUESTIONS YOU MAY HAVE ON LASER REFRACTIVE ERRORS CORRECTION BY LASIK / LASER PROCEDURE (PRK):
Q. Can this surgery correct all degrees of myopia?
The best results are obtained in persons who have either mild or moderate myopia (from -1.50 to - 6.00). These include a great majority of near sighted people.
Q. Will myopia be totally corrected?
Eyes treated with Excimer laser surgery (or radial keratotomy) have a high reduction in the amount of myopia. The ability to eliminate most or all of the myopia depends upon the amount of myopia present pre-operatively.
Q. Can this procedure correct astigmatism?
Excimer laser can correct up to 4D of astigmatism.
Q. Is the effect of the treatment permanent?
The refractive error of the eye stabilizes between 2 to 3 months after the laser treatment. The present studies have shown there has been no significant change after this initial period.
Q. Is excimer laser surgery safe?
Yes, it is safe because it does not affect any other eye structures.
Q. Are there any complications?
With any surgical procedure there may be complications.
- Dry eye and irritation.
- Possible residual refractive errors.
- Corneal Inflammation
- Electronic Scalpel complications.
Q. At what age can a person be treated?
The lower limit in our hospital is 18 years of age. There is no upper age limit to receive this treatment.
Q. When will the second eye be operated?
It may be treated at the same time or after the results of first eye are known.
Q. What does the patient need to cope with the difference between the two eyes if only one eye is treated initially?
A good way to balance the two eyes is to wear a contact lens in the non-operated eye. If the patient wears only glasses, a plain glass can be worn over the operated eye.
Q. Is the treatment painful?
The treatment is not painful as it is performed under local anesthetic drops. There may be significant pain during the following 24 to 48 hours. Drops and analgesics will be provided to control the pain.
Q. Will the vision return to normal immediately?
The healing process will be faster in Lasik surgeries compared with Laser surgeries (PRK) the majority of the improvement will be in the first days of surgery but in laser surgeries the improvement may extend to many weeks after surgery.
Q. What happens after the procedure?
The ophthalmologist will examine the eyes regularly at scheduled appointments and will give the instructions and sick leave accordingly.
Q. Can I pray and when I resume normal activities?
You can pray right after the treatment. You can resume your normal activities shortly after treatment as soon as the pain and discomfort has subsided. Swimming can be resumed 6 or 8 weeks after treatment.
Q. When will the patient return to driving?
Patient can drive after the prescribed period determined by the physian. Many patients could resume driving after 24-48 hours after surgery.
Q. Will the patient still need to wear contact lenses or glasses?
Most people will no longer need eye glasses or contact lenses. Patients over 40 may need reading glasses because in this age they need reading glasses whether they underwent a refractive error surgery or not.
Q. Will there be any effect on reading (close) vision?
The treatment should provide very good vision without glasses for far and middle range vision. Middle age patients may need reading glasses whether they underwent a refractive error surgery or not.