If you are considering laser eye surgery then you are likely to have heard of the potential night vision problems associated with the procedure. Along with dry eyes, night vision problems are one of the most likely side effects you will encounter following surgery. Night vision problems typically reduce over the first 6 months following your surgery and the vast majority of people manage without any serious difficulties. Such problems are more likely if you have a higher prescription that needs treating.
Understanding the causes will help in deciding which laser eye procedure you choose. Night vision problems are caused by higher order aberrations which can be made worse during laser eye surgery.
During a standard eye test your optician's equipment will typically only measure your low order aberrations which include short sightedness (myopia) long sightedness (hypermetropia) and astigmatism. These account for about 90% of your prescription (blurriness) and are easily corrected using contact lenses, glasses or standard laser eye surgery. However, virtually every eye also suffers from other types of optical errors (blurriness) called higher order aberrations (the other 10%). These optical errors are not measured during a normal eye test.
These higher order aberrations are typically responsible for vision problems such as glare, starbursts and haloes around lights. These cause problems especially in low light situations such as driving at night. Some people’s eyes will naturally have a greater amount of higher order aberrations than others and this is the reason some people suffer with night vision problems. Generally speaking higher order aberrations have very little effect on your day time vision. This explains why you could have perfect vision yet really struggle with night time driving. Your optician will tell you that your vision is perfect (remember your optician is only checking your lower order aberrations) yet you struggle with night vision.
As explained above, higher order aberrations result in problems with night vision and night vision problems are associated with laser eye surgery. But how are the 2 connected?
During laser eye surgery your cornea is reshaped to eliminate your prescription but it is not practical to reshape your entire cornea as this would involve removal of too much tissue and cause potential weakness in the surface of your eye. During laser eye surgery only the central part of your cornea is lasered and this is called the optical ablation zone. Beyond this central zone your cornea reverts back to its full prescription (what it was before your surgery) and this can become a problem in low light levels. During the day your pupils are small and so your vision will be perfect, however as the light levels reduce so your pupils enlarge and if they enlarge beyond the size of the optical zone you can have night vision problems. The average amount of the cornea that is lasered is about 6mm and if your pupils dilate beyond this during low light levels then you can see there may be problems.
It is generally accepted that Lasek has slightly less night vision problems compared with Lasik although the differences are not huge. The following explains why night vision problems are slightly less likely with Lasek:
It is rare however that you would choose Lasek over Lasik or vice versa on the basis of night vision problems. Your surgeon is the best person to advise you based on your pupil size, prescription and corneal thickness.
Although pupil size is not the only factor with night vision problems it is still the factor that surgeons take most seriously when considering surgery. It is generally agreed that if your pupil size at night is larger than the optical ablation zone (area of your cornea that has been lasered) then you are at a significantly higher risk of developing night vision problems. This is why it is extremely important that your pupil size is accurately assessed in low light levels prior to surgery.
As explained previously it is the higher order aberrations in your eye that give rise to night vision problems. Glasses, contact lenses and standard laser eye surgery do not take into account your higher order aberrations. Standard laser eye surgery can increase your higher order aberrations meaning night vision problems are possible.
Recent developments now mean that your laser eye surgeon can accurately measure your higher order aberrations using a Wavefront aberrometer. If you are found to already have a large amount of higher order aberrations or if you have large pupils your surgeon may insist that you have wavefront laser eye surgery.
A Wavefront aberrometer measures these higher order aberrations and this information can be used when your eyes are being lasered. So as well as just correcting your long sightedness, short sightedness or astigmatism (as with standard laser eye surgery) the laser is programmed to deliver a much more complex laser pattern. This custom/wavefront laser eye surgery will greatly reduce or eliminate your higher order aberrations as well as your normal prescription. Put another way, with wavefront laser eye surgery your eye is lasered according to the wavescan (high and low order aberrations) rather than by just the information calculated from a glasses (low order aberrations) prescription. For more information on Wavefront you can click here.
* It is important to mention here however that the latest generation of lasers have used this acquired wavefront data when developing their laser ablation profiles. This means that in many cases the results of laser eye surgery can be just as good with standard treatment as they are with wavefront surgery.
The vast majority of people notice very little difference in their night vision following laser eye surgery and those that do typically find it disappears over the 3-6 months following the procedure. If you have large pupils or already have night vision problems you may be advised to have wavefront laser eye surgery which can in some cases mean you have less night vision problems following your treatment than you ever did before.
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