关于激光视力矫正（更常被称为激光矫视手术 (LASIK)）的5个常见问题

Myopia is one of the most prevalent problems faced by Singaporeans and it reflects the visual environment its people are immersed in. Urban-dwellers, now more so than before, are dependent on their vision in both work and play. Nature and nurture both play a part in shifting the refractive state of entire generations of people to short-sightedness. Due to the dissatisfaction with reliance on optical aids like spectacles and contact lenses, laser vision correction has become increasingly popular in the past 2 decades.

Well, not at all. Spectacles for myopia (short-sightedness) minimize the actual image size, while those for long-sightedness enlarge images. They often cause aberrations with high power corrections. They can fog up in high humidity and may be cumbersome in sports. In comparison, contact lenses can provide excellent quality of vision, but if mishandled, can cause serious eye infections, which can leave the eye with permanent scars and reduced vision. It is a fact that the popularity of LVC contributed to a reduction of contact-lens related serious eye infections in many urban centres, saving many an eye from potential problems.

Due to the increasing focus on aesthetics, there are definite advantages in reducing one’s dependence on spectacles and contact lenses. LASIK stands for laser-assisted in-situ keratomileusis, which means laser-assisted sculpting of the cornea (the clear structure at the front of the eye). By “sculpting” we change the curvature and shape of the cornea, and its focusing power. In most cases, we aim to “neutralize” the errors of the eye’s power of focus, in order to return the eye to a state of zero power. It can be wonderful in restoring one’s unaided vision when done right, and freeing one from the possible problems associated with spectacle or contact lens wear.

One of the side effects of LVC is indeed its effect on the nerves supplying the cornea. In general, the higher the eye power treated, the more the cornea nerves affected. When the nerves are affected, they cause negative feedback which tricks the eye into thinking that it is not really dry, and hence tear production slows down. This is almost always temporary and recovers with time, but may take longer in those who had larger treatments.

An observation I made over my years in refractive surgery practice is that most candidates for these laser vision corrections are already suffering from dry eyes, often through poor contact lens tolerance. Laser treatment does not treat dry eyes, but they do work by getting unsuitable wearers off their ill-fitting contact lenses, which in the long term will contribute to restoration of the ocular surface.

There is no one treatment is better than the other. All eyes are unique and there are bound to be some individuals who are not suitable for a particular treatment. It is better to choose the best treatment technology for the individual’s eyes, rather than allowing the technology to choose its candidate, no matter how perfect it is touted to be. It is hence prudent to seek advice from a surgeon who is unbiased regarding the treatment options, or if necessary, ask for a second opinion from one who is able to offer a wide range of surgical options objectively.

Refractive surgery for presbyopia can be in the form of several options. A common solution is monovision LASIK in which one (dominant) eye is aimed for clear distant vision and the other for clear near vision, with small difference in power between the two eyes. This is usually comfortable after an initial adjustment period. This option can be considered for patients in their late thirties onward, and can also be performed with SMILE, TransPRK, ICL and even cataract surgery.

Like other parts of our body, the cornea and the eye may undergo some changes with age. In certain situations, LVC may potentially be repeated, or “enhanced”, if the eye’s measurements permit it. This may arise when the eye power regresses over time. Careful measurement and assessment should be done to rule out potential weakness (ectasia) of the cornea tissue, before such retreatments are performed. Thin corneas may have difficulty for retreatments by laser, but other approaches such as lens implants or exchange may instead be considered.