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Laser Eye Surgery (PRK and LASIK)
Two laser eye surgery techniques - photo-refractive keratectomy (PRK) and laser assisted in-situ keratomileusis (LASIK) - have been commonly used for correcting short sightedness (myopia), long-sightedness (hyperopia), astigmatism and presbyopia.
A refractive error is the term for a problem with the eye’s ability to focus images correctly. Light enters the eye through the cornea at the front of the eye, passes through the lens and alights on a point on the retina at the back of the eye. From here it travels along the optic nerve to the brain to form an image.
The cornea does most of the focusing, although the strength of the lens and the length of the eye are also factors. There are a number of conditions where objects can appear blurred because of focussing problems. These include:
Short-sightedness (Myopia) occurs when the light entering the eye focuses before the retina. With myopia distant objects seem blurry and near objects appear in focus.
Long-sightedness (Hyperopia) occurs when the light entering the eye focuses behind the retina. In this case both close and distant objects seem blurred, although distant vision is usually better.
Astigmatism occurs when the cornea is unevenly curved and appears more like a rugby ball than a soccer ball. This causes light to focus at multiple points within the eye leading to blurred vision.
Presbyopia occurs due to the decreased ability for the lens to change its shape with increasing age. It tends to develop in the mid to late 40s and presents as problems with near vision.
Non-surgical management of these conditions is with prescription glasses or contact lenses. During the 1980s an alternative treatment method was developed using the excimer laser. The excimer laser uses ultraviolet light to remove precise amounts of corneal tissue without damaging the surrounding eye tissues.
The two main techniques used in laser eye surgery for vision problems are photo-refractive keratectomy (PRK) and laser assisted in-situ keratomileusis (LASIK). Both forms of laser eye surgery are performed under high magnification with an operating microscope. Both are day stay procedures and take approximately fifteen minutes.
Photo-refractive keratectomy (PRK)
PRK has been used for treatment of focusing problems since 1988. It is most suitable for treating mild degrees of myopia. The surgeon uses a special instrument to remove the epithelium (layer of cells covering the cornea). The laser is then used to remove small amounts of tissue from the outer surface of the cornea. This alters the shape of the front of the cornea and so alters the ability of the eye to focus.
Laser assisted in-situ keratomileusis (LASIK)
LASIK is a more recent form of laser surgery and seems to provide improved results for people with greater degrees of myopia, hyperopia and astigmatism. With LASIK the surgeon creates a small flap on the surface of the cornea before using the laser to alter the shape of the underlying layers of the cornea. The flap is then repositioned and adheres within two to three minutes without the need for stitches.
Who Is Suitable For Laser Eye Surgery?
Laser eye surgery is suitable for people over 20 years of age who have had a stable glasses or contact lens prescription for approximately two years. It is also important that the eyes are otherwise in good health.
Laser eye surgery is not suitable if the cornea has become thin or protruded into a cone shape (keratoconus). Laser eye surgery is also not recommended for pregnant women, people with certain medical conditions or those taking medications that may slow wound healing eg: prednisone.
Prior to surgery the specialist will perform a detailed examination of the eye to determine suitability for treatment. At that visit a computer-generated map of the cornea will be developed and probable outcomes following surgery will be discussed.
People who usually wear contact lenses will be advised to remove these for a period of time before the operation. The specific length of time will vary depending on the type of lenses (hard or soft) and the surgeon’s preference.
If PRK is used, each eye is treated on separate days, with at least a week between each eye being treated. If LASIK is used both eyes can be treated on the same day.
Immediately prior to the procedure the eye will be anaesthetised using eye drops so that, although remaining awake during surgery, little or no discomfort will be felt. The eye not being treated will be covered to protect it from the laser light. A small speculum will be placed on the eye being treated, to prevent blinking.
Following PRK surgery either an eye patch or a soft contact lens bandage is applied. This is worn for a few days until the epithelium heals.
Following LASIK surgery a clear plastic eye shield is placed over the eye. The shield is usually removed the following day.
Driving home following laser eye surgery is not permitted so arrangements need to be made for alternative transport home.
Recovery times vary from person to person and also depend on the type of treatment received. Most people are able to return to work on the second day after the procedure.
Medication prescribed will include pain relief and eye drops (steroid and antibiotic). For PRK these drops are required for two to three months. For LASIK these drops are required for only one week.
Detailed instructions regarding care at home while recuperating should be provided upon completion of the procedure. It is important to follow these instructions carefully.
Following PRK
Moderate discomfort is expected for two to four days after PRK. Vision improves slowly over two to four weeks.
Following LASIK
Most people report only minimal discomfort following LASIK surgery. The improvement in vision is usually very rapid, although complete healing and stability of vision can take one to three months. Most commonly reported side effects include dry gritty eyes and sensitivity to glare. These are temporary in most cases.
Perfect results cannot be guaranteed with either procedure. Short-term complications following laser eye surgery can occur in some cases but they usually resolve by themselves or respond to treatment and are not expected to have any long-term effects on vision. Short-term complications can include:
- Photophobia (increased light sensitivity) may be experienced for one to three months following PRK and for one to two weeks following LASIK.
- Increased sensitivity to glare from oncoming car headlights or other bright lights in the evening may be noticed.
- Following PRK a sensation of a foreign body in the eye may be experienced.
- Infection is a possible complication following any surgery but this is very rare after laser eye surgery.
- Refraction after surgery can be slow to stabilise. It appears to reach stability between six and 24 months after surgery.
- Long term complications can also occur. These may include:
- Under-correction. This problem is less common following LASIK treatment than after PRK treatment. It is possible for revision of the surgery to be performed if necessary. If under correction persists it may be necessary to wear glasses or contact lenses.
- Over-correction. It is possible for over-correction to occur; making it necessary to wear glasses or contact lenses.
- Mild corneal haze is part of the healing process after PRK but can be more severe on occasions. If this occurs it can often be treated with further laser surgery.
- Following LASIK surgery there is the possibility of debris under the corneal flap or problems with the repositioning of the flap. If any problems do occur they can usually be effectively treated.
Anderson, K.N., Anderson, L.E. & Glanze, W.D. (eds.) (2006) Mosby’s medical, nursing, & allied health dictionary (6th ed.) St. Louis: Mosby-Year Book, Inc.
Auckland Eye (date unknown) Laser Surgery. Booklet. Auckland Eye. Auckland
MedicineNet (2007) LASIK Eye Surgery Foothill Ranch: MedicineNet Inc. http://www.medicinenet.com/lasik_eye_surgery/article.htm
Last Reviewed – 14/11/07
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