Two laser eye surgery techniques — photo-refractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) — are commonly used in New Zealand for correcting problems with the eye’s ability to focus.
The cornea and lens are mainly responsible for focusing the light that enters the eye, enabling a person to see objects clearly. However, a number of conditions can make objects appear blurred because of focussing problems:
- 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.
Non-surgical management of these conditions is with prescription glasses or contact lenses. During the 1980s an alternative treatment method was developed using special lasers to reshape the cornea. The two main techniques used in New Zealand are photo-refractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK).
Prior to surgery, an ophthalmologist (eye 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.
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 special tool will be placed on the eye being treated to prevent blinking.
Both forms of laser eye surgery are performed using a microscope under high magnification. Both are day-stay procedures and take approximately 15 minutes.
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. Your ophthalmologist will check for problems that may not make you a suitable candidate for the procedure.
- 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.
- Laser eye surgery may not be recommended for people with persistent dry eyes, eye injuries, or certain eye diseases including glaucoma and cataracts.
- People with certain autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis may be poor candidates for the surgery because their condition can affect post-operative healing.
- People who participate in sports like boxing and martial arts may not be good candidates for LASIK because there is a risk of corneal flap dislocation if the eye sustains major trauma.
Photorefractive keratectomy (PRK)
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.
With PRK, each eye is treated on separate days, with at least a week between treatments.
After surgery either an eye patch or a soft contact lens bandage is applied. This is worn for a few days until the epithelium heals. Moderate discomfort is expected for two to four days. Vision improves slowly over two to four weeks.
Laser assisted in-situ keratomileusis (LASIK)
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.
With LASIK both eyes can be treated on the same day.
After LASIK surgery, a transparent plastic eye shield is placed over the eye. The shield is usually removed the following day. Most people report only minimal discomfort following surgery. It is very important that patients not rub their eyes, as this can dislodge the corneal flap, potentially requiring an additional procedure to reposition it.
The improvement in vision after LASIK is usually very rapid, although complete healing and stability of vision can take one to three months. The most commonly reported side effects include dry gritty eyes and sensitivity to glare. These are temporary in most cases.
Recovery times vary from person to person and depend on the type of treatment received. Most people can return to work on the second day after the procedure.
Medication prescribed may include pain relief and artificial tears to relieve dry-eye symptoms, which most people experience immediately after surgery. Eye drops containing a corticosteroid to reduce inflammation and an antibiotic to reduce the risk of infection may also be prescribed. For PRK, use of these drops is required for two to three months. For LASIK these drops are required for only one week.
Perfect results cannot be guaranteed with either procedure. Short-term complications following laser eye surgery can occur in some cases. However, 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:
- Dry eyes due to LASIK surgery causing a temporary reduction in tear secretion.
- 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 the 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 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.
Mayo Clinic (2019). LASIK eye surgery (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/tests-procedures/lasik-eye-surgery/about/pac-20384774 [Accessed: 17/10/20]
O’Toole, M.T. (Ed.) (2017). LASIK. Mosby’s Dictionary of Medicine, Nursing & Health Professions (10th ed.). St Louis, MI: Elsevier.
O’Toole, M.T. (Ed.) (2017). Photorefractive keratectomy (PRK). Mosby’s Dictionary of Medicine, Nursing & Health Professions (10th ed.). St Louis, MI: Elsevier.
Royal Australian and New Zealand College of Ophthalmologists (2019). Refractive surgery (Pamphlet PDF). Sydney: RANZCO. file:///C:/Users/spin1/Downloads/Refractive%20Surgery.pdf