In 1990, when I started performing laser correction of vision, things were a lot simpler. When we performed photorefractive keratectomy (PRK), we would manually scrap off the most superficial layer (epithelium) of the cornea and laser the eye. There was no eye tracking so, patients had to keep their eyes steady for 1 to 2 minutes as the laser was very slow. Healing was slow and there was a lot of pain! Eyes were padded for 2 to 3 days! Having said all this, we had pretty good results with half of our patients having 6/6 to 6/12 vision (perfect vision to 100 degrees).
In 1996, I performed the first LASIK in Singapore. It was a lot more complicated with a mechanical machine (microkeratome) to cut open a thin slice from the cornea (flap) surface – open it up like in a book, lasering the surface just like a PRK and replacing the flap. Vision recovered a lot faster with a lot less pain. Within a week, the vision was perfect! However, only 70% to 80% had perfect vision and 60% to 70% of patients had night vision problems.
The Quest for better night vision – Wavefront-guided LASIK
Complaints of poor vision surfaced because day vision was excellent and there was a drastic drop in vision in dim light. Wavefront-guided LASIK was born! Defects in vision like glare and halos were caused by aberrations like spherical aberration and coma. These aberrations were caused by the poor shape of the cornea after LASIK surgery. Methods were devised to measure these defects and after years of improvements, the residual corneal shape after LASIK is now nearly perfect – hence the name, PerfectShape LASIK. However, different laser companies have different levels of success in developing these wavefront-guided treatments. SCHWIND Amaris lasers have been acknowledged by all surgeons to be the best Excimer laser in the world.
Other laser treatments
One of the biggest drawbacks was the need to make a LASIK flap. However, a flap was one of the best things about LASIK too! PRK continued to develop because it is a very economical procedure but had the disadvantage of slower vision recovery and discomfort after surgery. Pain management improved with the use of temporary “bandage” contact lenses. Scar development also was reduced by the use of a drug called “Mitomycin”, to prevent scarring.
LASEK and EpiLASIK developed at about the same time. LASEK was the use of dilute alcohol to remove the superficial surface layer (epithelium) of the cornea before PRK. EpiLASIK was the use of a blunt mechanical oscillating blade to remove the epithelium. Both techniques made the removal of the epithelium easier and more predictable. EpiLASIK however, had the added danger of inadvertently cutting and damaging the corneal surface. The latest development of laser surface treatments is called TransPRK. Previously, it had to be done in 2 stages. Now, with the SCHWIND Amaris laser, it can be done in one step. This is truly a no-touch all laser correction of shortsightedness and astigmatism. It is gentle and combined with wavefront-guided (corneal or total) treatment; it has been labeled by the industry as “Advanced surface ablation”. This technique is bladeless and flapless and is truly non-touch. Its only disadvantage now is a slower vision recovery (2 to 3 weeks).
Femtosecond laser – Flap cutting and SMILE
In the late 1990s, all flaps for LASIK were cut with mechanical blades. They were quite precise but like anything mechanical there was variable precision. The dawn of laser created flaps was initiated by a US company, the Intralase Company. Flaps created were now precise, predictable and had special edge designs to increase flap stability. Femtosecond created flaps became the standard of care because of their safety and precision. In early 2010, SMILE was conceived by the ZEISS Company. Instead of a flap, a disc of tissue is removed to correct vision problems. Initial results are promising however; there are still many problems to be solved. The disc is not easily removed and needs a lot of manual manipulation. There is no centering tracker to centre the disc removal. Even though there is no “flap”, patients still suffer from dry eye and a weaker cornea but, most disappointingly, astigmatic corrections and lower amounts of myopia are difficult to treat well. Enhancements for inaccurate corrections are very difficult to treat and may require advanced surface ablation! SMILE is a work in progress. It has promising results but, when compared to “All laser LASIK Xtra® with corneal wavefront-guided treatment”, SMILE is at present 2nd best.
Strengthening the cornea – LASIKXtra
The final iteration in laser procedures is strengthening the cornea. All laser treatments on the cornea weaken the cornea. But, recent developments and evidence show that we can strengthen the cornea after laser treatment with corneal collagen crosslinking – something which is now called LASIKXtra. Corneal collagen crosslinking is a technique that cause corneal fibres inside the cornea to “stick” together more strongly thereby increasing the cornea strength. Developed by Prof. Theo Seiler in the late 1990s, it is now the treatment of choice in many diseases that affect the cornea’s strength. By strengthening the cornea, we avoid complications that can happen with all forms of laser vision surgery.