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Refractive surgery refers to surgical procedures that aim to reduce or eliminate refractive errors of the eye.

The two most common and popular refractive surgical procedures are Laser In-Situ Keratomileusis (LASIK) and Photorefractive Keratectomy (PRK). Both methods utilise the excimer laser.

Photorefractive Keratectomy (PRK) uses the excimer laser to re-shape the surface of the cornea thereby changing its curvature. No incisions are made. This is an effective method and has excellent results. However, recovery of vision takes slightly longer and initial discomfort is expected.

Laser In-Situ Keratomileusis (LASIK) is a modification of PRK. A microkeratome is first used to create a thin flap of corneal tissue. This flap is folded over and the excimer laser is used to sculpt the exposed corneal bed. The flap is then replaced.

Wavefront-Guided LASIK customises the exact laser pattern for each individual’s eye. Each person’s eye has minor optical imperfections that are unique to each individual, similar to fingerprints. With wavefront technology, these imperfections can be detected and analysed by an aberrometer. The data obtained is fed into the excimer laser machine, which in turn, customises the exact laser pattern to treat not only myopia and astigmatism, but also these minor optical imperfections.
Wavefront guided LASIK may be better suited for patients with more complex prescriptions and unusual corneal shapes.

Iris Recognition Technology & Multi-Dimensional Eye Tracker
More commonly known for its function as a high security tool, iris recognition and tracking technology has been harnessed by the LASIK team at Tan Tock Seng Hospital and National University Hospital to enhance the visual outcomes in LASIK procedures.

In customized Wavefront LASIK, it is essential that there is an exact point-to-point application of laser pulses onto the cornea based on the Wavefront information of the patient's eyes obtained during the pre-operative examination.

There are three potential errors which may occur in the process of transferring a patient's wavefront data to the laser machine. These errors could affect the predictability of the surgery's outcome and limit the success level of the operation:

1. Eye Rotation
During wavefront-guided LASIK, patients have their corneas mapped before the operation while seated. However, the laser procedure is carried out when the patient is lying down. This positional change sometimes causes the eye to rotate (cyclotort) between 6 to 15 degrees, thus misaligning the mapping.

2. Shift in pupil centres
Wavefront examination is performed with a medically-dilated pupil, while laser is done with a constricted pupil. Misalignment also occurs when there is a shift in the pupil centres due to the contraction or expansion of the iris.

3. Eye movement along x-, y- and z-directions
The iris tracking technology accounts and corrects for the eye rotations and the pupil centre shifts. It further enhances safety as nobody's iris is the same, hence the laser will never be applied on the wrong person or even the wrong eye.

The multi-directional eye tracker locks onto rotation movements of the eye within its socket as well as the eye's horizontal and vertical movements; unlike traditional scanners, which were limited to following an eye's movements along x and y-axis only.

This will further enhances the safety and outcome of customized Wavefront LASIK.

Phakic Intraocular Lenses (Phakic IOLs)
A Phakic IOL is an artificial lens that is surgically inserted inside the eye in someone who still has their natural crystalline lens (ie. they are phakic)

Both the lens and the cornea help to focus light onto the retina, thus allowing a person to see clearly. Some refractive errors can be corrected by altering the shape of the cornea, such as laser procedures like LASIK. For others, particularly severely short-sighted people, LASIK may not be suitable and these people are more suited to Phakic IOLs. Another difference between LASIK and Phakic IOLs is that laser surgery is permanent and irreversible, whereas it is possible to remove a Phakic IOL.

The Phakic IOL that we implant sits in front of the natural lens and is clipped onto the iris, which is the coloured part of our eye that controls the amount of light that enters. It is custom-made and works like a contact lens, except that it is placed inside the eye.

The possible complications of Phakic IOLs include inflammation, glaucoma (high intraocular pressure), damage to the cornea and/or cataract formation.

Potential candidates for Phakic IOL implant will undergo thorough pre-operative examination and tests before confirming suitability for the procedure. The patient must have had a stable prescription for at least one year. The minimum age limit is 21 years and they must have good general eye health.

As with all types of surgery, there are some risks involved and these need to be discussed in detail with the surgeon during the consultation.