A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

My right eye sees colors differently from my left eye. Is that normal?

May 30, 2014

Dear Cecil:

I’ve noticed sometimes colors look different when I alternate eyes. It's easiest to perceive when looking at something that’s soft white. When I close my right eye, the white has a bluish tint to it; when I close my left eye, it has a reddish tint. Is there a name for this? Is this normal, am I insane, or do I have some special kind of vision? It's been like this since I was a kid.

Cecil replies:

Hard to say what’s going on — the medical literature is pretty thin. But my guess is there’s a researcher or two who’d love to get a look at your eyes.

Here’s what we know:

1. The closest I can find to a name for what you describe is unilateral color blindness, a condition in which one eye has normal color vision and the other doesn’t. I’m far from certain that’s what you’ve got. Those with UCB tend to think one eye is bad and the other good, not that both eyes skew equally to opposite ends of the spectrum. You might take one of those online color vision exams, testing one eye at a time, and report back. Pending further insight on that score, we’ll call your condition differential color vision.

2. UCB is generally described as rare. DCV may not be. Whenever someone posts online saying they’ve got it, dozens of others chime in to say “me too.”

3. There are several well-established reasons for a difference in color perception between eyes. The first involves defects of the cornea or lens. One of the first symptoms of cataract — an opacity in the lens — is that objects become blurry and have a yellow-brown tint. Typically this affects one eye but not the other, or both eyes but to varying degrees.

4. With age, the lens commonly hardens and becomes denser, causing it to scatter blue and violet light. This will make purple objects appear redder to older people, and blues will appear less vibrant. But the effect is usually the same for both eyes, and you say this is something you’ve noticed since childhood. So that probably isn’t what you’ve got.

5. Another thing that may contribute to a difference in color perception is an artificial lens, or no lens at all. I’m assuming this doesn’t apply to you, Drew; I mention it because it’s interesting. The lens normally helps filter ultraviolet light; once it’s gone, or replaced with a non-filtering artificial lens, you can see UV light, which is perceived as whitish blue or violet. A famous example is the French Impressionist painter Claude Monet. Monet suffered from cataracts late in life and to remedy this had the lens in his right eye removed in 1923. The effect on his vision, it’s claimed, can be seen in the series of paintings he produced from 1922 to 1924 known as The House Seen from the Rose Garden. The first works in the series feature warm colors, such as reds, browns, and yellows; those completed after the operation, though depicting the same scene, are dominated by blue and violet.

6. Another reason for a difference in color perception is disease-caused damage to one of the optic nerves. One of the diagnostic rules of thumb taught to medical students is that color vision anomalies affecting just one eye are “acquired color vision defects,” which generally are a sign of disease or some other condition picked up after birth. In contrast, garden-variety color blindness, which affects both eyes equally, is usually congenital. The importance of this distinction is that acquired color vision defects likely indicate a problem requiring treatment, whereas congenital defects don’t.

7. But there are exceptions, which brings us back to unilateral color blindness. A number of research papers appearing in the 1940s through the 1970s called attention to cases of congenital (that is, inherited) color blindness affecting one eye only. In unilateral deuteranopia, for instance, one eye lacks all or most of the cones that perceive green, sharply limiting the number of colors that can be distinguished, while the other eye is normal. But the affected eye can be easily identified — it’s the one that can’t see reds and greens (the paler shades anyway). That doesn’t describe you.

8. Some, my assistant Fierra for one, can induce the effect you describe by lying on their sides for a few minutes and looking at a white field. Fierra reports that from the eye closer to the ground colors seemed redder, bluer from the other. Others say merely closing one eye for a while gives the same result.

9. The right/left split of the brain may also play a role. For example, a test of reaction times found subjects responded quicker when they viewed objects displayed on a red background with their left eye than with their right. With objects displayed on a green background, the results were reversed.

In sum, we haven’t a clue. Clearly this is a promising field of study for an enterprising grad student. We await further reports.

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