Do Large Pupils Cause Night Vision Problems After LASIK Laser Eye Surgery?

Patients with Large Pupils Can Enjoy Good Night Vision After LASIK With Customized Wavefront Laser Eye Surgery. In a recent blog, I looked at how the development of Customized Wavefront LASIK has largely solved the issue of night vision problems after LASIK. Night vision problems were mostly associated with the use of conventional, non-Wavefront LASIK.

Today, a patient from Camarillo came to see me for a consultation with another issue regarding night vision after LASIK that I am often asked. This patient had been told that her pupils were too large and that this would cause a problem with her night vision if she had LASIK. In fact, this was not the case and this patient, who did have large pupils, could still undergo Customized Wavefront LASIK and expect night vision as good as — or better than — her current night vision with glasses or contacts.

This patient had heard an explanation that many patients and even some ophthalmologists that I have taught have also heard. This explanation says that if the pupil gets bigger than the laser zone at night, it will let it light around the edges of the laser zone and cause night vision problems. While this explanation about the role of the large puil in night vision may make sense if not examined carefully, it turns out the optical situation involving large pupils and night vision is much more complex. In fact, large pupils per se do not cause night vision problems in and of themselves. Many people with very large pupils can have excellent night vision after LASIK, particularly if Customized Wavefront LASIK is performed.

The first clue that large pupils do not directly cause night vision problems after LASIK came from two outstanding studies of LASIK and night vision conducted several years ago. The first one, conducted by the US Navy, showed that by 6 months after LASIK, patients with large pupils had night vision equal to patients with smaller pupils. In fact, the study looked back at pre-operative characteristics of patients undergoing LASIK and found that the degree of pre-operative nearsightedness — and not pupil size — was the most accurate predictor of who would develop night vision problems: the more the pre-operative myopia (nearsightedness), the greater the chances of night vision problems. Another study done in Canada of 795 patients undergoing LASIK came to similar conclusions: pre-operative levels of nearsightedness were correlated to the risk of night vision complaints after surgery while pupil size, whether large or small, was not a risk factor for night vision problems.

So what does cause night vision problems after LASIK and why have some patients with large pupils ended up with night vision problems? As discussed in my previous blog, conventional LASIK tends to increase a distortion called “spherical aberration” in proportion to the degree of correction being performed. Higher degrees of conventional correction result in greater degrees of spherical aberration being inscribed into the cornea. It is of note that both of these studies were done with conventional LASIK, which explains why patients with higher degrees of correction had greater chances of night vision problems: they had higher degrees of spherical aberration after their laser eye surgery.

Another critical concept to understand is that the larger the pupil, the greater the amount of total distortion is being presented to the optical system of the eye. This has nothing to due with light rays sneaking around the edge of the ablation zone. However, if a patient underwent conventional LASIK for correction of a high degree of nearisghtedness, then quite a bit of spherical aberration would end up in the cornea. The larger the pupil, the more this aberration distorts the optical system — whether or not the pupil actually is larger than the laser zone. This is why the ultimate specific pupil size was not a risk factor in these studies as, for all patients, their pupil was larger at night than during the day, which degraded vision more for those with more spherical aberration.

Customized Wavefront LASIK tends to induce far less spherical aberration in the cornea than conventional surgery and also attempts to identify pre-operative spherical aberration and treat it. Therefore, the overall degree of aberration of the cornea typically is less than with conventional surgery, so a large pupil would be expected not to present the problems it does with conventional surgery.

Several studies have, in fact, confirmed that patients with large pupils can successfully undergo Customized Wavefront LASIK even for very high degrees of correction. In the FDA clinical trial which led to the approval of the VISX CustomVue method of performing Customized Wavefront Surgery, patients with larger pupils were actually more likely to notice an improvement in their night vision after surgery than patients with smaller pupils. This finding was confirmed in a recent study of 51 patients by Ed Manche, M.D. of Stanford University which showed that patients with large pupils had no night vision disturbances after Customized Wavefront LASIK.

Of course, LASIK is still a surgical proceedure and complications can happen, including to night vision outcomes. The data, however, shows that patients with large pupils typically can expect excellent night vision after Customized Wavefront LASIK.

In a future blog I will tell you about a patient of mine that really exemplifies this. This patient had previously undergone conventional LASIK elsewhere and came to see me with complaints of terrible night and low light vision after his previous surgery. He had a very large pupil. When I saw him for his consultation, it was obvious his problem was not his pupil size, but the enormous degree of spherical aberration that had been put into his cornea during his conventional LASIK surgery. We were able to perform a theraputic Customized Wavefront treatment and eliminate his night vision problems. His pupil, of course, was still just as large after our Wavefront correction, but his night vision problem had been resolved with the reduction of his spherical aberration. This was a case in point that aberration, not pupil size, was the root problem for this patient with large pupils.

Do Large Pupils Cause Night Vision Problems After LASIK Laser Eye Surgery?

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