LASIK For Myopia

Dr. Mansoor A. Farooqui

LASIK for Myopia (Nearsightedness) and Astigmatism

Introduction
The options for correction of myopia and astigmatism now include glasses, contact lenses, and different kinds of refractive surgery such surface treatment by photorefractive keratectomy (PRK), and Laser Assisted in Situ Keratomileusis (LASIK) using excimer lasers. The goal of LASIK is to reduce your need for glasses or contact lenses by changing the shape of the cornea through LASIK laser surgery.
 

How the Eye Functions
The cornea and lens of the eye focus light like a camera lens to form an image on the retina at the back of the eye. The cornea, where light first enters the front of the eye, provides about two thirds of the eye's focusing power, and the lens inside the eye provides the other third. Normally, in relatively young persons (i.e., less than 50 years of age) the lens of the eye can adjust its focusing power somewhat, so you can see objects clearly both near and far away. The eye focuses light by refracting all light rays to meet at a single point. If the focusing process works perfectly, a sharp image of the object, you are looking at, will be focused exactly on the retina and you will see a clear image. However, if the light focuses either in front of or behind the retina, the image on the retina (and the image you see) will be blurred, and you are said to have a refractive error. Refractive errors are not diseases, but are common variations observed in human beings across the world. There are three main types of refractive error. They are called nearsightedness (myopia), farsightedness (hyperopia) and astigmatism. The amount of refractive error present in the eye is measured in units called "diopters." When your eye Cannot focus correctly, it is said to have one of the main refractive errors: myopia or hyperopia.
Myopia usually starts in childhood and typically stabilizes in the late teens or early adulthood. The tendency to develop myopia also runs in families. Myopia can change from a very mild to a very strong nearsighted effect.
Hyperopia is also very common, and is especially problematic in older persons who have difficulty in focusing on objects up close. 
Astigmatism occurs when the refractive error is stronger in a particular direction. Astigmatism may occur with either myopia or hyperopia. The following pictures emphasize the role of the cornea in determining the focusing power of the eye. They show that the more sharply the cornea is curved, the more the light rays are bent. If the cornea is curved too much, the image focuses in front of the retina and the eye is nearsighted. If the cornea is too flat, the image focuses behind the retina and the eye is farsighted (Fig. 1). When the cornea shape is just right the image from a distant object is focused exactly on the retina.

 

Fig. 1: This proper focus for distance vision is called emmetropia. Good focus depends on three factors, the overall shape and size of your eye, the shape of the cornea, and your lens power. During a regular eye examination, your doctor checks your vision to determine where the eye focuses light relative to your retina. When your doctor adjusts your vision with different lenses, he correctly focuses light on the retina.  Myopic individuals see near objects clearly, but distant objects are blurry. Nearsightedness and astigmatism can be corrected by any method that reduces the total refractive power of the eye, and includes the use of glasses, contact lenses and refractive surgery. With glasses or contacts, changes in your vision that occur slowly over time can be corrected by simply adjusting the lens prescription of your glasses or contacts. Refractive surgery, on the other hand, produces changes that are permanent.
 

What is LASIK?
LASIK is laser surgery to correct nearsightedness (myopia) with or without astigmatism. An excimer laser beam is used to flatten the middle layer of the cornea. The laser beam removes microscopic amounts of tissue from the middle layer of the cornea, precisely reshaping the cornea. The excimer laser produces a beam of ultraviolet light in a series of rapid pulses. Each pulse lasts only a few billionths of a second and removes a microscopic amount of tissue by evaporating it (fig. 2). Excimer laser light does not penetrate the eye and leaves other eye structures (iris, lens and retina) undisturbed. The laser produces very little heat and is controlled by the doctor during the operation. Prior to LASIK, some anesthetic drops are placed on the eye to numb it. Your doctor then begins the LASIK procedure by cutting a thin flap on the front of the cornea using a special cutting instrument called a micro-keratome or using a special laser machine called intralase. The doctor will then fold back this flap of tissue much like opening a hinged cabinet door.
Folding back the flap will give the doctor access to the middle layer of the cornea where the laser treatment will be performed. This part usually takes a couple of minutes. After that, your doctor uses the laser beam to perform the LASIK procedure. The laser treatment usually lasts only about 10 -15 seconds.  After the laser treatment is complete, the doctor will carefully fold the flap of cornea tissue back into place to complete the procedure.  

Fig.2

Contraindications, Warnings & Precautions Contraindications

You should not have LASIK surgery if:

  1. You have collagen vascular, autoimmune or immunodeficiency diseases (for example: rheumatoid arthritis, lupus or AIDS). These conditions may result in scarring or poor healing after LASIK treatment resulting in reduced vision.

  2. You are pregnant or nursing. These conditions may affect your preoperative refraction making it difficult to choose the correct amount of LASIK treatment.

  3. You show signs of keratoconus (thinning of the cornea) or corneal disease. This condition can lead to serious cornea problems that require additional surgical repair and result in poor vision.

  4. You have a condition which would stimulate large amounts of scar tissue (keloid formation). Scarring can be permanent and may require surgery to repair.

  5. You are taking prescription medications that affect corneal healing or your refraction. You should discuss all medications you take, even over the- counter medications, with your eye doctor. Many medications can affect the way your cornea is changed by the laser and the way it heals after LASIK treatment. These may affect your refractive outcome and possibly result in reduced vision after LASIK treatment. 

Warnings

  1. Your nearsightedness is changing. If your vision is unstable, then you should not be treated. Treatment of unstable vision may affect the accuracy of your refractive results.

  2. You have severe allergies. Your medications may have to change before or after your eye surgery. These medications may change the wetness (moisture level) in your eye. If the medication changes the wetness of your eye, the accuracy of your refractive results may be affected.

  3. You have been diagnosed with ocular Herpes simplex or ocular Herpes zoster. Herpes are viral infections. Laser treatment may reactivate the infection.

  4. You have nystagmus (uncontrolled eye movements) or another condition that prevents a steady gaze.

  5. You need to be able to keep your eyes still during treatment. 

Risks & Benefits

Risks
LASIK is a laser surgical procedure involving your eyes and has some risks. You should consider and discuss with your doctor the risks that are noted here. These are based on clinical experience with LASIK cases and the possibilities that doctors believe should be considered for this kind of eye surgery.

  1. At the time of surgery, it is possible that the flap will not be cut correctly. In some cases, the flap of tissue may not be the correct size or shape or may be too thin. In these cases, the doctor may have to stop the surgery, fold the flap into position, and allow it to heal. In most cases, the doctor can complete surgery at a later date. In the studies on LASIK, the majorities of these cases were completed later and had a successful result.

  2. Although the effects of LASIK on visual performance under poor lighting conditions have not been determined, it is possible that you will find it more difficult than usual to see in conditions such as very dim light, rain, snow, fog or glare from bright lights at night. These effects have been reported as being more common in persons with large pupils (over 6 mm). It is possible that these may be permanent effects.

The first week following surgery: The following complications have been reported up to several weeks following LASIK treatment. They are associated with the normal healing process after treatment and include:

Discomfort,  pressure feeling, scratchiness, burning sensation, and dryness may last for up to 1 day after surgery, for which your eye doctor can provide medications.

  1. The feeling that something is in your eye.

  2. Swelling of the cornea.

  3. A problem with healing of the corneal flap, including damage to the flap, loss or misalignment of the flap, or growth of cornea surface cells under the flap. If needed, the doctor may lift the flap to clean the middle layer of the cornea and reposition the flap to improve healing.

  4. Blurred vision and tearing or watery eyes may occur as the cornea and the flap heals in the first few hours.

  5. Sensitivity to bright lights may occur in first few hours.

The first two or six months following surgery:

  1. Your intraocular pressure may increase due to use of steroid or anti-inflammatory medications (0% to 0.1% of eyes had a significant elevation in intraocular pressure in this time frame). This is usually resolved by drug therapy or by stopping the use of steroid or anti-inflammatory medication.

  2. Hazy or cloudy vision rarely occurs after LASIK surgery (<1.0% of eyes had mild or moderate haze with no significant loss of vision).

  3. An increase in fluctuation of vision (40.0% pre-operatively vs. 64.3% post operatively).

  4. Glare (35.7% pre-operatively vs. 35.7% post-operatively).

  5. Difficulty in night driving.

CAUTION: You should contact your doctor if you notice any pain or change or loss of vision in the eye. Eye pain or sudden loss of vision can indicate a serious problem that required immediate medical attention.

One year after surgery: At one year after LASIK surgery the following vision-threatening events happened:

1.      Over correction.

2.      Losing a significant amount (more than 2 lines lost on an eye chart) of vision even with glasses.(0.6%)

3.      If the results of the surgery are not satisfactory, you many need to have additional LASIK surgery in the same eye.

 

Benefits

  1. LASIK surgery is effective in reducing nearsightedness requiring correction from -1.00 to -11.00 diopters spherical equivalent in patients with 0.00 to -4.00 diopters of astigmatism.

  2. LASIK may reduce overall nearsightedness (95% significantly improved uncorrected vision to the level of 20/40 or better at 6 months).

  3. LASIK may reduce or eliminate dependency upon contact lenses or glasses (> 90% could see 20/20 or better without glasses or contacts at 6 months).

  4. LASIK should be considered a permanent surgical procedure, in that the refractive result changes little after the first few months. If your refractive result is unsatisfactory, your doctor may recommend further surgical treatments, or correcting your remaining refractive error with glasses or contacts.

Are you a good candidate for LASIK?

If you are considering LASIK you must:

  1. Be at least > 18 years of age.

  2. Have healthy eyes which are free from eye disease or corneal abnormality (for example:Scar, infection, etc.)

  3. Have nearsightedness (myopia) requiring vision correction between -1.00 and -14.00 diopters spherical equivalent, with 0.00 to -4.00 diopters of astigmatism.

  4. Be sure your eye doctor has satisfactory evidence that your refraction has been stable over the past year (changed by less than or equal to 0.5 diopters in your vision correction, or by less than or equal to 0.5 diopters in your astigmatism correction).

  5. Be informed of LASIK risks and benefits as compared to other available treatments for nearsightedness (myopia) and astigmatism.

  6. Be willing to sign an informed consent form, as provided by your eye care professional.

 Summary of Important Information

  1. LASIK is a permanent operation to the cornea that cannot be easily changed.

  2. Alternatives to LASIK include glasses, contact lenses, PRK.

  3. LASIK is not a laser version of radial keratotomy (RK); they are completely different from one another.

  4. Some occupations, such as pilots, do not accept applicants who have had any refractive surgery.

  5. Refractive error must be stable (within 0.5 diopters in your vision correction, or within 0.5 diopters in your astigmatism correction) for at least one year before surgery.

The following risks of LASIK surgery should be noted:

  • Temporary discomfort may be expected for 24-72 hours after surgery. If the discomfort persists, please contact your doctor.

  • Problems that may last several days: corneal swelling, blurred vision, feeling something in the eye, shadow images, light sensitivity, tearing, and pupil enlargement.

  • Adverse events beyond the first few months: elevation of intraocular pressure,  cloudy cornea affecting  vision, overcorrection, under correction or nearsighted, loss of best vision that can be achieved with glasses <o.1%, damaged corneal flap 1 in 800 ghost images.

The following benefits of LASIK surgery should be noted:

  • Nearsightedness with astigmatism may be reduced so that the amount of time contact lenses or glasses are used during the day is reduced or eliminated.

  • LASIK may be an alternative to glasses in some patients who are intolerant of contact lenses.

  • LASIK may be another alternative to correct nearsightedness and astigmatism.

Patients considering LASIK surgery should:

  • Discuss fully with one or more ophthalmic surgeons the complications of LASIK surgery, the risks and the time required for healing, and have a complete eye examination before making a final decision.

(Dr. Mansoor A. Farooqui acquired fellowship in ophthalmology from College of Physicians and Surgeons of Pakistan (CPSP) and Fellowship of Royal College of Surgeons of Edinburgh (FRCSED) in ophthalmlogy. His special interests are surgeries for the removal of eye glasses. He has done more than 6000 surgeries LASIK, PRK, Epilasik, Lasek and Intralasik procedures. He has special certification for the verisyse and ICL (specialized lenses to correct higher degree of refractive errors) 


 

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