It is important to note that the term night vision refers to visual distortions in dim light or artificially lit environments, and not specifically in very dark settings. Examples of the various light environments are:
Photopic – vision in bright daylight (when pupils are the smallest)
Mesopic – vision in artificial and quite dim light (when pupils are larger than in photopic light)
Scotopic – vision in no lighting (when pupils are the largest)
In 2004, researches found the pupil size of patients seeking refractive surgery ranged from 4.3 to 8.9 millimeters, with the average being 6.5 millimeters. This is an important number to remember because the area of the cornea that is fully treated during a LASIK procedure is called the optical zone. A common laser optical zone is currently 6.5 millimeters. If the laser's optical zone is smaller than the patient's dark-adapted (scotopic) pupil diameter this results in loss of contrast sensitivity and visual disturbances such as glare, starbursts and halos. The greater the disparity between the laser's optical zone and scotopic pupil size, the more severe the visual disturbances. The importance of pupil size in refractive surgery (LASIK) is well established.
In April 2009, the U.S. Navy's Department of Refractive Surgery published a landmark study that evaluated night vision results of standard (traditional) microkeratome (bladed) LASIK compared to Custom all-laser Wavefront IntraLase. It was concluded that Custom Wavefront IntraLase significantly improved night driving performance and outperformed standard (traditional) microkeratome (bladed) LASIK. Here are the results of the Navy's study:
In this study, patients were tested with a Night Driving Simulator before LASIK and again 6 months after LASIK. Each patient's night vision was assessed by the ability to recognize real-life night driving scenarios such as freeway signs, road hazards, and pedestrians. From this study it was concluded that:
Custom Wavefront IntraLase patients resulted in a higher percentage of 20/20 or better results as compared to standard (traditional) bladed LASIK procedures
Custom Wavefront IntraLase patients almost never experienced night vision disturbances, and often experienced an improvement in night driving performance
The majority of Custom Wavefront IntraLase patients were very satisfied with their LASIK outcomes
Results show that Custom all-laser Wavefront IntraLase is ten-times more likely to improve night vision, rather than induce night vision disturbances such as night glare and halos.
Fortunately, for the vast majority of LASIK patients, night vision disturbances are a temporary side effect during the healing process; typically resolving within a few weeks, if not days, following the LASIK procedure. The risk of experiencing night vision disturbances can be dramatically reduced when using a skilled surgeon and the state-of-the-art technology available with the VISX CustomVue Wavefront mapping and IntraLase laser system.
What is CustomVue LASIK?
CustomVue LASIK is a custom LASIK procedure that uses the latest digital technology to sculpt and enhance the cornea. When the shape of the cornea is sculpted, light enters the eye and properly focuses on the retina to deliver clearer vision.
What is Wavefront mapping?
Wavefront mapping generates an extremely accurate topographical scan of the cornea; with advanced technology to identify both higher and lower order aberrations. This data becomes part of the surgeon's treatment plan to be used during the LASIK procedure.
What are Higher Order Aberrations and Lower Order Aberrations?
Higher order aberrations refers to minute corneal imperfections that cause night vision disturbances and difficulty with contrast sensitivity.
Lower order aberrations refers to the major corneal imperfections that cause nearsightedness (myopia), farsightedness (hyperopia) and astigmatism.
Wavefront mapping accurately maps both higher and lower aberrations; whereas standard (also referred to as traditional) LASIK is only able to correct lower order aberrations, which is why greater numbers of patients who have traditional LASIK experience night vision disturbances such as night glare, starbursts and halos as compared to Wavefront patients.
We have discussed CustomVue Wavefront IntraLase technology, but what about the actual lasers? When comparing lasers you will hear the terms: Wavefront-guided, slit-scanning and spot-scanning. And, as you might imagine, each does something slightly different.
These are the most commonly used laser LASIK procedures. Spot-scanning lasers are also known as flying-spot lasers. Spot scanning lasers are often used to treat patients with irregular astigmatism, as they allow for customized treatments and have the potential to produce the smoothest corneal treatments.
These lasers use small beams linked to a rotational device with slit holes that gradually enlarge,little by little increasing the lasers optical zone. Slit-scanning laser have the highest risk of over-correction or decentered treatment.
Wavefront-guided treatments can be used with both slit and spot-scanning lasers. These lasers are connected to a device that allows the surgeon to look at how light travels through the eye. Using wavefront technology, the surgeon can create a totally customized LASIK treatment for each patient.
An automated eye-tracking system monitors the movement of the eye to ensure the laser's beam remains on target throughout the duration of the procedure. Eye-tracking systems are used to reduce complications and produce better results.
What is the best procedure and laser to reduce night vision disturbances? Without a doubt, and with studies to support the claim, CustomVue Wavefront IntraLase LASIK is the superior LASIK procedure – with fewer patients experiencing night vision disturbances following CustomVue Wavefront IntraLase LASIK and ten-times more likely to improve night vision than other forms of LASIK.
It is more difficult to compare lasers as this would require a large patient sample using side by side comparisons using different lasers on the same patient. However, here are some differences between the three (3) most widely used lasers, and surgeon preferences, based on a 2008 annual survey of the American Academy of Ophthalmology / International Society of Refractive Surgery:
VISX Allegretto Bausch and Lomb
Star S-4 IR WaveLight
U.S. Market Share 67% 18% 7%
Custom Wavefront Yes Yes-Limited Range Yes-Limited Range
Type of Laser Beam Spot-Scanning Spot-Scanning Spot-Scanning
0.65 to 6.5mm .95mm 2.0mm
Treatment Zone 4.5 to 9.5mm 5.2 to 9.0mm 7.0mm
Fourier Algorithm Yes No No
3-D Eye Tracking Yes No No
Iris Registration Yes No No
When considering LASIK, it is important to choose a skilled surgeon who uses the latest technology – CustomVue Wavefront IntraLase LASIK for the best results...vision you can count on, both day and night.
Check out our other LASIK blogs:
- LASIK Screenings
- LASIK over 40
- PRK versus LASIK
- Monovision LASIK
- Custom LASIK
- Different Lasers
- Preparing for LASIK
- LASIK Recovery