Who knows what darkness likes in the heart of my left eye?

August 18, 2008 5:43 AM

One of my eyes adjusts to darkness much faster than the other. In fact, I'm pretty much blind in one eye for at least half an hour after the lights go out. I've always had this and assumed it was just me. But it turns out my mother has this as well. I'm not worried about it, but what is it?

This sounds like night-blindness, but it doesn't really fit with any of the night-blindness conditions I've googled. It's more like prolonged dark-adaptation. It only happens when there's a big difference in light-levels and the darkness is pretty dark, so walking into a dark room from a sunny street wouldn't do it, but turning off the lights of a brightly lit room at night would. After maybe thirty minutes the affected eye catches up with the other one.

Aside from this, my mother and I seem to have healthy vision (though we're both slightly long-sighted). We've both had this as long as we can remember (probably from birth, but definitely from childhood). I don't think either of us have ever asked an optician about this - it's one of those things that has always been there and doesn't really affect our lives at all, so it's just not something that comes up. I'll probably ask at my next appointment, but I've only just had my last one so it's not for a couple of years.

I've done some googling and haven't found anything that makes sense. On the other hand, maybe I'm going off on completely the wrong tack and this is actually something common that I've somehow not heard of. Or maybe we're hitherto undescribed by science. Like I say, I'm not worried, just curious.

posted by xchmp to health & fitness (4 comments total)

IANAD, naturally, but it sounds like you have a condition where one of your eyes has low-functioning or a lot fewer rods. Given there are other genetically-linked photoreceptor conditions, I wouldn't be surprised yours is too, but the one eye part is rather interesting. At least, so long as it doesn't get worse, it's not a disease but probably a hereditary condition. Very curious! There must be a fancy name for this, but if not, you could contact a university clinic and maybe lead to a new study.
posted by Ky at 7:33 AM on August 18, 2008

I have this, too, and always attributed it to my astigmatism. I also see different colored halos on each side of a light, even the moon--one side edges yellow and the other blue. Do you have astigmatism? It seems to be hereditary too; both my parents had it.
posted by Riverine at 9:45 AM on August 18, 2008

Riverine: I have a very slight astigmatism. My eyes do perceive colours slightly differently (one sees warmer colours than the other). There was a recent question about this. Given the number of responses in that thread, it seems fairly common. It does seem different to your halos, though, which sound a lot like a chromatic abberation.

When you say both your parents had it, do you mean the astigmatism or the prolonged dark-adaptation thing?
posted by xchmp at 10:25 AM on August 18, 2008

My more astigmatic eye *appears* to adapt to dark much slower.

However, I think some of what we call night vision is clever "edge detection" circuits in the brain, which would rely a good deal on crisp focusing ability.

I think my edge detection circuits aren't getting to grips with the boundaries between dark and slightly less dark areas, and consequently, I see a continuum of shade, and therefore I can't really discriminate between the darker and slightly less dark areas.

Several optical illusions such as the chess board illusion show that we can't really distinguish different shades without them being adjacent and clearly so.
posted by blue_wardrobe at 10:51 PM on August 18, 2008