I had a patient this week who presented with a complaint that "everything looks green, especially when I'm reading off of white paper." As she was an elderly retiree, and reading was one of her few pastimes, this was especially troubling to her. Psychological studies have shown that a green color near the center of the visible spectrum of light wavelengths is supposed to be the most pleasing to the human eye, but it wasn't to this frustrated lady.
My first thought was that she may have had cataracts developing, as people will report their vision taking on a yellow, orange, or brown color as cataracts develop. Maybe if hers were turning yellow, it was such an intense yellow she may have perceived it as green. However, she had already had cataracts removed from both eyes several years ago, so that was not the case. I then wondered if her implanted lenses had some kind of green tint to them, maybe an ultraviolet blocker, but examination of the implanted lenses revealed them to be crystal clear, and ordinary implants.
My next thought was that maybe her maculas were starting to degenerate, and the blue, yellow, and red receptors were degenerating faster and earlier than the green receptors. I went along with that as a working hypothesis and tried to figure out how to solve her problem. Half from memory, and half from pulling up a color wheel on the internet, I identified the color opposite green, found that it was red, and asked one of the opticians if we had a pink or red colored tint sample that I could have her look through. We found a pink/brown combination lens, and then a pure pink lens, and held them up in front of her reading glasses. Immediately her hunched-up shoulders relaxed, she let out a sigh of relief, and said, "Yes. That's perfect!"
There is a small subfield of optometry know as Syntonics, that promotes the idea that colors, filters, and tinted lenses can affect how we perceive the world and how our visual systems function. While there isn't a lot of published scientific evidence to back it up, this appeared to be one case where we could solve a functional visual problem, with a simple tinted lens that would normally have been used for cosmetic purposes!