What causes halos after LASIK?

You’re not going to be walking around with a glowing ring floating over your head. But after Laser Eye Surgery you are likely to experience another type of halo effect.

Halos are a form of glare that temporarily affect vision after Laser Eye Surgery. They occur mainly at night and in low light conditions, appearing as bright circles around light sources such as headlights or street lamps.

Not so much a side effect in the most common sense of the word — an unintended and often seemingly unrelated consequence of a medication, drug, or surgery — halos are a healthy sign that the eye has begun the recovery process, accumulating beneficial fluid in the cornea in the form of swelling.

As a part of the eye’s natural recovery process, every patient who has Laser Eye Surgery can expect to encounter glare — regardless of age, prescription, technique, or individual prescription. Other than halos, glare can also manifest in the form of starbursts, which, rather than being a ring around lights, appear more like a dispersed glow.

The extent to which this affects a patient’s life is generally minor. It’s even common for patients not to notice glare like starbursts and halos at all, while those who do simply avoid doing any significant amount of night driving for a while.

The real side effects of Laser Eye Surgery

Expert Laser Eye Surgeon Mr Glenn Carp explains the effects of night glare after Laser Eye Surgery.

In the first few weeks after Laser Eye Surgery, patients may also experience minor fluctuations in their quality of vision as it stabilises as well as dry eyes (for which clinics provide lubricated eye drops). In the vast majority of cases, all of these effects are mild and gradually disappear over the first few days or weeks.

After around the three-month mark, swelling in the cornea will have settled along with any visual disturbances. Regarding halos, it’s not uncommon to have a little residual night glare after this time. But if it’s severely disrupting your vision, it’s a good idea to visit your clinic for further testing. There a surgeon can identify the source of the issue and see if there’s a problem that needs to be addressed.

It is possible for night glare and halos to persist long-term after laser refractive surgery. This is most often related to a residual refractive error due to under or overcorrection – a small residual prescription or astigmatism can cause halos as well as blurred vision.

If your eyes were made of plastic, the accuracy of the laser would mean that the outcome would always be 100% perfect. However, as the eye is a biological system, an over or under correction can result from individual healing response relative to the average person. Fortunately, the course of action is relatively straightforward — with many patients benefitting from having a simple follow-up procedure or wearing glasses at night.

However, persistent night glare and halos can also occur even if the refractive outcome is perfect. Night vision symptoms were one of the major side effects of laser refractive surgery during the 1990s with the first generation lasers. These were caused by the shape of tissue that was removed by the laser and the area over which the shape change was performed. If the treated area was smaller than the pupil (particularly at night where the pupil becomes larger), the edge of the treatment zone would cause halos around lights.

Over the last 20 years, there have been significant improvements made to the lasers and how to change the shape of the eye, so that a clinic with the right technology can minimize the risk of halos. This includes changing the tissue removal to be an aspheric shape (rather than a spherical shape) that is a better match to the natural state of the cornea (the front window of the eye), and increasing the treated area to be larger than the pupil.

The risk of night glare and halos is now very low for modern lasers, but the risk does increase for higher prescriptions and in patients with large pupils. This is one of the reasons why the assessment before surgery is so important. If you are at an increased risk, this will be identified and discussed during the assessment before surgery.

But even if you do experience long-term night vision symptoms, we now have the technology to reduce these in a custom treatment based on topography scans of the cornea — these scans provide a map of the corneal surface and the laser can be programmed to make the surface smoother, improving the quality of vision in the process. This technology is not available at every clinic, so it is worth asking about a clinic’s experience with “topography-guided treatments.

Contact us today to find out more about how our comprehensive assessment process or to book your consultation.