Statistically, which LASIK procedure has the least likelihood of residual degree after the surgery?

In terms of residual degree after the surgery, we have to consider the accuracy of the pre-operative manifest refraction, which can be affected by various factors such as accommodation (the focusing ability that can be too strong, commonly noted in children and young adults). This is the reason why your ophthalmologist may choose to do a cycloplegic refraction during your pre-laser evaluation. During the cycloplegic refraction, your eyes will be dilated and the internal eye muscles thoroughly relaxed. This is to prevent one from accommodating, which can result in a falsely high refraction result, and serves as a double-check to ensure the manifest (pre-dilation) refraction is accurate.

Generally speaking, the higher one’s refractive power, the higher the chance of having residual degree after surgery. For example, a person with a 1,000 degrees is more likely to have some residual degree than a person with 300 degrees.

Currently, there are 3 types of laser vision procedures (LVC), namely

1. Advanced Surface Ablation (PRK, Epi-LASIK, LASEK)
2. LASIK
3. and ReLEx SMILE.

The lasers used for the above procedures are highly accurate and precise which result in the conception that they are some high-tech science fiction, whereby a blast of the lasers can correct one’s refractive error down to absolute zero. Indeed, if the lasers were applied on a piece of steel, it is highly possible to achieve that.

However, many failed to realise that the lasers are applied on the eye, which is a living thing. The only thing we cannot predict is how the eye heals after laser surgery. There are many factors which contribute to a residual degree and you should discuss with your eye surgeon before making a decision which laser treatment to go for.

There is as far as I know, no reliable statistical data to allow a definitive answer to this question. By this, I mean there are no well conducted, randomised blinded controlled trials comparing different procedures with respect to residual refractive error. As I mentioned in another answer, a Cochrane Database meta-analysis showed similarly good outcomes between LASIK and PRK at one year, but this is in no way a 'statistical' validation of their equality.

There are many factors that can contribute to 'residual degree', and the type of procedure used is probably a minor one when compared to the others. Also, bear in mind that in the first place, significant residual degree after laser refractive surgery is a rare occurrence.