Refractive Disorders
In a normal eye, light entering the eye is refracted (bent) first by the eye’s cornea and then by the eye’s natural lens so that it focuses precisely on the retina. The retina is the sensitive tissue on the back of the eye that converts light images into electrical impulses and sends them through the optic nerve to the brain. If the light rays are not focused precisely on the retina, the result is refractive error, or poor vision in the form of nearsightedness, farsightedness or astigmatism.
Nearsightedness (myopia)
Nearsightedness occurs when the eye’s cornea is shaped too steeply, or the eye is too long. Incoming light rays are refracted to a focal point in front of the retina instead of on the retina. This results in distant objects being out of focus, while close objects can be seen clearly.
Farsightedness (hyperopia)
Farsightedness is the reverse of nearsightedness. Instead of a cornea that is too steep, the farsighted eye has a cornea that is too flat, or the eye is too short. Light rays refracted through the cornea converge at a focal point behind the retina. This results in close objects being out of focus while distant objects are more clear.
Astigmatism
Astigmatism is the result of an aspheric (irregularly shaped) cornea that scatters light rays as they enter the eye. An astigmatic cornea has an oblong shape like a football instead of a round shape like a basketball. The result is that there is no single focal point, and vision is blurry both near and far.
Presbyopia
Presbyopia refers to the normal process of aging in which the natural lens inside the eye becomes hardened. As this occurs, the lens loses its flexibility, which makes reading difficult. This usually occurs between the ages of 40 and 50. Everyone experiences presbyopia. The result of this normal process is bifocals for those who wear glasses or contacts, and reading glasses for those who have not needed corrective lenses previously. LASIK surgery will not correct presbyopia.
Correcting Refractive Disorders
Wearing corrective lenses merely treats the symptoms of nearsightedness, farsightedness and astigmatism. The lenses do not correct the refractive error. Those with nearsightedness, farsightedness and astigmatism can benefit from refractive surgery because refractive surgery corrects the error by enhancing the eye’s ability to refract light rays precisely onto the retina.
Many people think that LASIK is the only type of refractive surgery, and today LASIK is the most commonly performed corrective eye surgery in the United States, but in truth, there are many different procedures to choose from. Refractive surgery, also known as corrective eye surgery, encompasses a multitude of procedures designed to treat and correct refractive errors including nearsightedness, farsightedness and astigmatism. In each of these procedures, a laser is used to reshape the cornea to alter the way light rays enter the eye to achieve focus. The process used, however, differs from surgeon to surgeon.
LASIK
Laser in situ keratomileusis, or LASIK, is the most commonly performed refractive surgery procedure today and is the primary procedure of choice at Wolfe Eye Clinic. LASIK has advantages over other procedures, including a relative lack of pain and the fact that good vision is usually achieved almost immediately or in a very short period of time. Those with nearsightedness, farsightedness and astigmatism can benefit from LASIK. During LASIK surgery, a thin flap of tissue is created on the center of the cornea (Figure 1). This flap is then lifted back to expose the internal tissue, or stroma, of the cornea. An excimer laser is then used to reshape the cornea and correct the refractive disorder (Figure 2). The flap is then layed back over the cornea where it heals itself in a very short period of time (Figure 3).
With LASIK, the instrument used to create the flap varies. Most surgeons use an instrument called a microkeratome. A microkeratome is a device that uses a very sharp oscillating blade to cut the flap. Other surgeons, including those at Wolfe Eye Clinic, prefer a more advanced bladeless technique, using a very precise laser to create the flap instead. Wolfe Eye Clinic surgeons use the IntraLase laser to create the flap during LASIK surgery.
The Zyoptix z-100 is a major advance in treatment. It has advanced safety features that include iris recognition that ensures treatment for the correct eye and rotational eye tracker that ensures greater precision. This treatment is twice as fast and is suitable for a greater variety of abnormalities. It affords excellent results.
The advantages include:
- Iris Recognition- Greater accuracy of treatment placement
- Automatic patient identification ensures correct eye is treated
- Zy-ID – A unique digital ‘map’ of the iris, individual to every patient
- Multidimensional Eye tracker- Compensates and corrects for intra-operative eye-movement in every dimension, including cyclotorsion and pupil shift
- 100Hz Laser- For significantly faster treatment times
- Treatment planner- For wide range of treatment options
- LED Illuminations- For greater pupil iris contrast, greater surgical visibility and improved comfort for patients and surgeons
- Zeiss Microscope- Increases visibility by allowing for 3 levels of magnification.
- With the latest technology at the hands of skilled professionals, the Centre ensures the best results possible.
PRK
Photorefractive keratectomy, or PRK, was the first refractive procedure that utilized the excimer laser to reshape the front surface of the cornea. It was initially envisioned in 1983 and, after a long series of clinical trials, was approved by the FDA in 1995. PRK however is primarily used to correct mild to moderate cases of nearsightedness and astigmatism. After the eye has been anesthetized with topical eye drops, your doctor prepares the eye by removing the surface layer of the cornea called the epithelium. This layer naturally regenerates itself every few days. Pulses of laser light are then applied to the surface of the cornea to reshape the curvature of the eye. Postoperatively, patients typically wear a bandage contact lens for the first three to five days to reduce postoperative pain and irritation. Anti-inflammatory eye drops are used in a decreasing dose for several months. Vision is usually blurry initially and starts to clear over the first several weeks, while continuing to improve for up to one year.
LASEK
Laser Epithelial keratomileusis, or LASEK, is a laser procedure that is used mostly for people with corneas that are too thin or too flat for traditional LASIK. It was developed to reduce the chance of complications that occur when the flap created during LASIK is not the ideal thickness or diameter. In LASEK, the epithelium, or outer layer of the cornea, is cut not with the microkeratome blade or laser used in LASIK, but with a blade called a trephine. Next, the surgeon covers the eye with an alcohol solution for around 30 seconds. The solution loosens the edges of the epithelium. After sponging the alcohol solution from the eye, the surgeon uses a tiny tool to lift the edge of the epithelial flap and fold it back out of the way. Then the surgeon uses an excimer laser, as in LASIK or PRK, to apply pulses of laser light that sculpt the corneal tissue underneath. Afterward, the epithelial flap is placed back on the eye. There is a possibility of a reaction to the alcohol that may kill some of the epithelial cells. Patients typically wear a bandage contact lens for around four days and may feel eye irritation during the first few days afterward. The time it takes to recover good vision is up to four to seven days longer than with LASIK.
Epi-LASIK
Epi-LASIK is a cross between LASIK and LASEK. During Epi-LASIK, a flap is cut in the cornea’s outer layer, just as in LASIK and LASEK. However, with Epi-LASIK the surgeon uses a blunt, plastic oscillating blade. Instead of the alcohol that is used in LASEK to loosen the epithelial sheet, during Epi-LASIK the surgeon uses the blunt plastic blade, called an epithelial separator, to scrape the sheet across the eye. Next, the surgeon uses an excimer laser, as in LASIK, LASEK or PRK, to apply pulses of laser light that sculpt the corneal tissue underneath. Afterward, the epithelial flap is placed back on the eye. Then, a special contact lens is placed on the eye to keep the flap in place while it re-epithelializes. Vision will probably be cloudy or variable at first, unlike traditional LASIK. Some patients report good vision within a week or two, while others take three to six months to reach their final result. These recovery times are significantly longer than with LASIK, which usually allows people to achieve good vision from the same day up to a few weeks later and to drive by the day afterward.
Lens Implants — An Alternative to LASIK
LASIK surgery is not an option for everyone. A very high refractive error, thin corneas or severe dry eye may prohibit someone from being a good LASIK candidate. Fortunately, implantable lenses may provide an alternative. Examples of these lenses include the Verisyse™ Intraocular Lens, Visian’s Intraocular Collamer Lens, Alcon’s Acrysof® ReSTOR® Intraocular Lens and the ReZoom™ multi-focal Intraocular Lens. Unlike LASIK, which reshapes the outer part of the eye, lens implants are inserted inside the eye. Once in place, the lens stays in place indefinitely and should require no maintenance.
