What causes halos after LASIK?
You’re not going to be walking around with a glowing ring floating over your head, but after having Laser Eye Surgery you are likely to experience another type of halo.
Halos are a form of glare that temporarily affects 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 a 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 the eye has begun its 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 profile. Other than halos, glare can manifest in the form of starbursts, which, rather than being a ring around lights, appear more like a dispersed glow.
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The extent to which this affects a patient’s life is minor. It’s common for patients not to notice glare like starbursts and halos at all, while even those who do may simply avoid doing any significant amount of night driving for a few weeks.
Mr Glenn Carp explains the effect of night glare after Laser Eye Surgery.
In these first few weeks after Laser Eye Surgery, patients may also experience minor fluctuations in quality of vision as it stabilises and also dry eyes (for which clinics provide lubricated eye drops). In the vast majority of cases, all of these things 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 undercorrection 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 to minimize the risk of halos. These include 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 corrections and in patients with large pupils. This is one of the reasons why the assessment before surgery is so important. If you have an increased risk, this will be discussed during the assessment before surgery. The good news though, is that 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.”
Again, these scenarios are extremely unlikely given a thorough screening process — something we at London Vision Clinic are particularly known for.
Contact us today to find out more about our screening process or to book your consultation.