[visionlist] Info on "coloured filters" sought

[m.coleman at surrey.ac.uk]

Dear Michael,

I can only really comment on the Irlen lenses side of things. Some additional search terms that may be helpful:

'colorimetry', 'Meares-Irlen', 'overlays', 'scotopic sensitivity' - may bring up some related papers.

Agree there is a limited selection of literature on this topic with regard to reading difficulties. Griffiths et al. (10.1111/opo.12316) sum up the issues nicely. I've used coloured overlays extensively in clinical practice and my experience is that while they can be incredibly effective in certain individuals, the evidence base for predicting which patient characteristics are indicative of a strong response is very limited. Another key issue is differentiating between visual stress symptoms originating from a treatable binocular vision problem and those that can be addressed only via coloured filter. There's also a lack of consistency in the thresholds for prescribing overlays as well - in the Scottish NHS the threshold was a 30% improvement in reading speed for prescribing the chosen overlay after successful treatment of any co-existing binocular vision problems, but this is not consistent across the UK or internationally. 

I also had one memorable patient who did not require an overlay, but in fact experienced almost a 'reverse' form of Meares-Irlen syndrome - they were incredibly symptomatic for text on yellow paper, with a great reduction in reading speed, but had no issues with white or other colours. Interestingly, there is little focus on this kind of (probably rare) phenomenon in the existing literature on the topic. There is also little exploring the idea that giving an overlay where one was in fact not required may be detrimental to a child's educational development. I think there is a great need for more qualitative research in this area to accompany the quantitative approaches.

Regarding other uses for coloured filters, they are gaining more traction in the 'blue light' screentime controversy with regard to improving sleep quality.

That's all I can really contribute, apologies it's not the robust evidence you were hoping for but hope it provides a little insight.

Best wishes,
Dr. Marianne Coleman
Research Orthoptist
University of Surrey

-----Original Message-----
From: visionlist [mailto:visionlist-bounces at visionscience.com] On Behalf Of Prof. Michael Bach
Sent: 20 November 2017 09:43
To: cvnet <cvnet at mail.ewind.com>; visionlist at visionscience.com
Subject: [visionlist] Info on "coloured filters" sought

Dear Vision Friends:

Supposed to write a review on coloured filter glasses ('twas a situation where I couldn't really say no), I have a hard time finding good literature on this. “Good” here means solid science, experiments preferably performed in blinded fashion – to the degree "blind" is possible with tinted glasses :). If this interests you, I would value your input, and specifically on these topics:

• Just my limited English? Search terms "filter", or "colored filter", or "tinted glasses / lenses" or else?

• Contrast: How can contrast improve, when by design there is less information behind a wavelength-selective filter than before it? One exception: short wavelengths suffer more scattering, so removing them can help. But is there more?

• In rod monochromacy (achromatopsy), reducing total light flux by 10–100 times helps by avoiding rod saturation. Orange filters can do that, and have the added “social” bonus that other people can see the eyes. Or is there an additional bonus to orange glasses over strong neutral density filters (with equivalent rod-weighted flux reduction)?

• In various retinal dystrophies (e.g. cone dystrophy or RP), tinted glasses are supposed to help. How does this work beyond "psychology"? Are there reliable experiments?

• A sideline: Does the spectral absorption of the juvenile lens change over, say, 0–10 years of age?

• Why do people with beginning media opacities like sunglasses? The contrast, be it quantified in Michelson or Weber, remains numerically identical. Is it a nonlinearity or “just psychology” (not meant pejoratively)? Methinks head sunshades (visors) would help more.

• “Brightening” glasses. There are types of sunglasses making the world appear brighter. How does that work?

• I'm sure there are many occupation-specific hazards (e.g. glassblower cataract, welder's flash) where filters help. Am I missing something important here?

• I am sceptical about the Irlen-type filters and the buzz (SSS) around them. Are there any reliable, robust findings? [I am _not_ trying to start a *storm!]

• I don't believe you can “cure” colour blindness / deficiency by tinted glasses. [Possible exception: creating interocular differences.]


I apologize for the lengthy post, all ignorance on my side, and value all advice on any of the above topics from you.


With my best regards,
Michael.
-- 
Prof. Michael Bach PhD, Eye Center, University of Freiburg, Killianstr. 5, 79106 Freiburg, Germany. 
Michael.Bach at uni-freiburg.de   <http://michaelbach.de>
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