Standard or conventional LASIK was a good procedure but in recent years there have been many excellent improvements in the LASIK procedure. Newer laser software and hardware have improved vision correction for both day and night conditions.
Like other parts of our body, our eyes are unique to us in terms of their shape and characteristics. Just as we can have tailor-made clothing to fit our bodies, we can have customised LASIK treatment for our eyes. Wavefront-guided LASIK is a powerful tool, especially in the hands of an experienced surgeon, just like a piece of cloth in the hands of a master tailor.
Wavefront-guided treatments are especially useful in re-treating patients with problems that persist after standard/conventional LASIK surgery.
Wavefront-guided, customised ablation – also known as aberrometer guided laser treatment – has its basis in astronomical optics. When astronomy research was being carried out in the 1960s, astronomers and physicists developed special techniques to improve poor and degraded images of stars and planets. Since then, these same techniques have been used to guide the excimer lasers used in LASIK treatment. The principle of wavefront-guided LASIK is simple. There are
3 different systems that can be used to obtain a wavefront of the eye. They are the Hartman-Shack, Tscherning and skiascopy systems. Light in various forms is projected into the eye. It is reflected, and as it exits the eye, is deviated. The light exiting the patient’s eye is then compared to the “ideal” eye. The wavefront of a patient’s eye is obtained by calculating the light ray deviation from the “ideal” eye.
Wavefront analysis has also helped increase doctors’ understanding of patients’ visual problems, especially their complaints of poor vision after refractive surgery. This wavefront analysis has helped in the development of newer and better techniques for LASIK.
Wavefront analysis of patients’ eyes after LASIK, PRK, LASEK and epi-LASIK treatment revealed that the standard/conventional treatments were aggravating some visual distortions (aberrations).
Detailed analysis showed that in these patients’ initial surgeries, the amount of laser energy that reached the eye was less than predicted, particularly in the peripheral parts of the cornea. This caused the peripheral areas of the cornea to be under-corrected, leading to poor contour profiles in the corneal periphery. The analysis also showed that the effective laser treatment area was smaller than expected, giving patients smaller real optical zones. As better night vision requires larger optical zones, it was no surprise that many patients complained of poor night vision after standard/conventional LASIK surgery.
Excimer lasers like the SCHWIND Amaris 1050RS laser compensate for this, leading to dramatic improvements in optical zone size. The use of abberration-free LASIK treatment has led to a considerable decrease in night vision problems. Other laser companies are only now following suit, adding this feature to their newer lasers.
Topography-guided LASIK was first performed in the late 1990s. However, after some initial excitement, there was little progress because of the development of wavefront-guided LASIK. In 2003, there was a revival of interest in topography-guided LASIK as there were limitations to what wavefront-guided LASIK could do.
A corneal topographer is a machine that measures the corneal shape and contour. Topography-guided LASIK uses this corneal contour map to guide the Excimer laser ablation pattern.
Topography-guided LASIK is advantageous especially when the cornea has been previously treated with a corneal refractive procedure. Distorted corneas from previous treatments can be re-treated to make them regular and smooth once again – like “wiping the slate clean”. Topography-guided LASIK has been able to help many patients with unsatisfactory results from previous standard / conventional LASIK treatment.
Most visual aberrations originate from the cornea. LASIK treatments used to correct them are usually either wavefront or aspheric. Wavefront treatments do not factor in the shape of the cornea during treatment, and aspheric treatments do not consider the wavefront.
Patients who undergo standard LASIK or epi-LASIK treatments that use either wavefront or aspheric profiles run a higher risk of having poor night vision, which may be distorted by glare and halos.
PerfectShape® LASIK (Corneal Wavefront-Guided LASIK) is the latest available customised treatment technique. It combines the best aspects of all previous programs into a single entity and improves on all prior treatment profiles. It customises the treatment to an individual’s eye, taking into account the original corneal shape, wavefront and asphericity. This treatment simultaneously regularises the cornea and modifies it into a “perfect” shape. This gives patients superior corneal contours, and this results in excellent day and night vision.
In the distant future, there is technology that can further enhance the already excellent LASIK results.
In all LASIK ablations, the final shape of the cornea is calculated without knowledge of the length of the eyeball. Ray tracing, as the name suggests, traces a ray of light through the tear film, cornea, aqueous, lens, vitreous and finally to the central region of the retina called the macula.
This ray tracing technique calculates the best corneal shape to make all rays of light strike accurately onto the centre of the macula. This will make LASIK ablation calculations theoretically even more precise. Initial results for this technique are excellent. However, this technology is not yet available commercially.