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 by an ophthalmologist (eye specialist). Both are day-stay procedures and take approximately fifteen minutes.
Photo-refractive keratectomy (PRK)
Laser assisted in-situ keratomileusis (LASIK)
Who is suitable for laser eye surgery?
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.
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.
Medication prescribed will include artificial tears to relieve dry-eye symptoms, which most people experience immediately after surgery, pain relief and eye drops containing a corticosteroid to reduce inflammation and an antibiotic to reduce the risk of infection. 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.
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.