A small study published in Optometry and Vision Science1 has added to the debate surrounding the value of blue blocking (BB) lens filters to minimise near work-induced asthenopia.
The study followed 23 young, visually normal subjects who were required to perform a 30-minute reading task from a tablet computer.
Their digital screens were overlaid with either a BB (which blocked 99% of the wavelengths between 400 and 500nm), or a neutral-density (ND) filter producing equal screen luminance. Accommodative response, pupil diameter, and vertical palpebral aperture dimension were measured at zero, nine, 19, and 29 minutes after the start of each reading task and participants completed questionnaires to quantify symptoms immediately following each session.
The researchers concluded, “A filter that eliminated 99% of the emitted blue light was no more effective at reducing symptoms of digital eyestrain symptoms (DES) than an equiluminant ND filter. There is little evidence at this time to support the use of BB filters to minimise near work-induced asthenopia”.
Tim Thurn, Professional Services Director at Essilor ANZ said the results were not surprising, given the demographics of the group analysed. “Such a group is not necessarily reporting DES, so to find that either type of screen overlay made no difference is really not very surprising,” he said.
Mr Thurn highlighted a similar study published in IOVS,2 which had a different conclusion. A slightly larger participant group of 36 healthy subjects (20 male; 16 female) was tasked with online reading for two hours (as opposed to 30 minutes) and randomised to wearing no block, low blocking, or high-blocking eyeglasses. A masked grader measured eye fatigue via critical flicker fusion frequency (CFF) and evaluated symptoms of eye strain via a 15 item questionnaire before and after computer use.
The researchers found significantly less fatigue, less pain and less itch among participants wearing high block lenses. “Our results support the hypothesis that short wavelength light blocking eyeglasses may reduce eye strain associated with computer use based on a physiologic correlate of eye fatigue and on subjects’ reporting of symptoms typically associated with eye strain,” they wrote.2
“Overall we know that the rationale for blue light and screens is the improvement in contrast. This is something that Dr Maitreyee Roy and her PhD student at UNSW are looking at, as part of their assessment of blue blockers,” said Mr Thurn. He added, “There is a need for a large well controlled study encompassing and controlling for more factors in DES and for symptomatic and asymptomatic patients.”
Lens expert Nicola Peaper, who works with Rodenstock, agrees that more research is required. “I think the profession is in agreement that when dealing with DES there is no one fix that will work for all patients. The process must start with a full visual and binocular examination and a detailed visual task analysis. This forms the basis of the advice issued to the patient and should include advice on positioning of screens and ambient lighting. The correct choice of lens to allow for good posture at all times during the task is then essential.
“Personally, I believe that the use of an antireflection coating will ensure visual comfort for screen users as it will cut down on internal reflections and back surface reflections from the spectacle lens and so reduce distracting and discomforting glare,” said Ms Peaper.
“There is not enough research to give a definite answer as to how effective, or indeed necessary, reducing blue wavelengths of light is to comfortable use of digital devices. The idea of improving comfort comes from the fact that blue wavelengths are the shortest in the visible light spectrum and most likely to scatter. This scattering can produce glare and reduced contrast leading to asthenopia. Also, as stated in the article published in Optometry and Vision Science,1 blue light may interfere with the body’s circadian rhythm, so that blue light exposure in the evening may interfere with the ability to sleep.
“There is no research around the question of how much blue light would need to be removed to reduce any symptoms. The main thing for practitioners to understand is how much blue light reduction is being given to a patient. With the majority of main stream solutions, be they tints or coatings, there is around a 10 to 20% reduction in blue light – obviously not the 99% blocker used in the trial. Additionally, mainstream solutions are worn for at least as long as the patient is using a device, which can be over 10 to 12 hours daily.
“Whilst there is some reported perception of improved comfort from these tints and coatings, I believe, at this stage more research is needed.”
References:
- Palavets T, et al. Optom Vis Sci. 2019;doi:10.1097/ OPX.0000000000001318.
- iovs.arvojournals.org/pdfaccess.ashx?url=/data/journals/ iovs/935965/ on 08/25/2017
