A Ray Of Light For The Myopic

Dr Law demonstrating how the new Advanced Control Eye-Tracking technology works.


NEW technology with the ability to track rotation of the eyeball during laser eye surgery is offering hope to those with serious myopia and astigmatism. Such patients were previously deterred from opting for Laser-Assisted In situ Keratomileusis or LASIK, a type of refractive laser eye surgery used to correct myopia (short-sightedness), hyperopia (far-sightedness) and astigmatism, said consultant ophthalmologist and eye surgeon Dr Michael Law Sie Haur.

The new technology called Zyoptix Advanced Control Eyetracking (ACE) adjusts for eye rotation in any direction within 15 degrees during LASIK surgery, thus ensuring that the laser beam is always aimed at the correct intended spot on the cornea.
TDuring LASIK, a thin flap of corneal tissue is cut and then peeled back from the front of the cornea (the transparent covering over the pupil). The laser gently vaporises away some of the corneal tissue beneath the flap to make the cornea a slightly different shape to correct pre-existing refractive errors. The flap is then placed back over the front of the eye.

Explaining the significance of ACE, Dr Law said prior to the new technology eye rotation during surgery affected the predictability of outcomes, which was why doctors often discouraged patients with significant short-sightedness and astigmatism from opting for LASIK. “Studies have shown that in 8.3 per cent of surgeries, the eye rotates by more than three degrees, up to a maximum of 19 degrees, and this would affect the outcome of the surgery, especially in those with very bad myopia and astigmatism when treatment covers many sessions.

Designed to improve patient safety, ACE is the world’s first Dynamic Rotational Eye-Tracking (DRET) system that constantly tracks eye movements during application of the laser, while simultaneously adjusting the laser ablation pattern for the duration of the LASIK treatment. “The ACE system reduces the risk of misalignment and improves compensation for eye movements, thus correcting for both eye rotation and pupil centre movement with different pupil diameters.

DRET provides added safety by stopping the laser if the eye moves too fast for it to be safely followed by the eye tracker. Dr Law said by following the iris and the rotations of the eye, the outcome for patients, especially those with a high degree of astigmatism and myopia, is much improved because the system accurately maps the laser pulses on the part of the cornea where the surgeon is working.

Dr Law said LASIK is now as safe as contact lenses as the probability of the treatment causing a significant loss of vision is about 0.01 per cent. The procedure is rapidly being acknowledged as a viable alternative to glasses and contact lenses for people suffering near- and far-sightedness, with over 16 million worldwide having had LASIK to date, according to the American Society of Cataract and Refractive Surgery.

“Contact lens wearers have a one per cent risk of developing a serious contact lens-related eye infection over 30 years of use. “There is also a 0.05 per cent chance of experiencing significant vision loss as a result of such infections over the same period.”

Types of refractive errors

GOOD vision is the result of sharp images being focused on the retina (the sensory nerve layer of the eye). The optical system of the eye, which consists of the cornea, lens and vitreous body, bends rays of light to focus exactly on the retina of the eye. This bending of light rays is called refraction.

Refractive errors of the eye occur when the cornea and the lens do not properly focus the light rays on the retina.

In normal vision (emmetropia), the focusing powers of the cornea and the lens are perfectly matched to the length of the eye ball.

In myopia, the most common type of refractive error in Asia, the cornea is too curved for the eye ball. Distant objects cannot be seen clearly because light rays are focused in front of the retina. A person with myopia is able to see clearly close objects, whereas those at a distance appear blurry. In hyperopia, individuals are able to see far objects relatively sharply but not so with closer things. The cornea is too flat or the lens too weak for the length of the eye ball. As a result, the cornea and the lens focus the light rays behind the retina.

In astigmatism, images of objects at close and far distances appear distorted. Usually the reason for this is the shape of the cornea, which resembles more the shape of an egg than that of a ball.

The result is that light rays are bent in different directions and do not focus on one refractive point on the retina.

(Taken from The New Strait Times Online)