reading in the dark

Factual Questions
1

Ok, this has been bugging me for years. When I was younger my parents would always tell me to turn on more lights if i was reading and they didn’t think it waslight enough, because reading in poor lighting can somehow damage your eyesight. Then at university I learnt that it just ain’t so, which makes sense. After all, the only thing that could get strained is the muscles controlling the shape of the cornea and don’t muscles get better with use instead of worse. However, I didn’t pay too much attention to that lecture and now nobody will believe me when I tell them that reading in poor lighting doesn’t damage your eyesight; can any of the Teeming Millions give me the juice on this?

It only hurts when I laugh.

2

I’m exactly like you in terms of knowledge. IMO reading in the dark shouldn’t damage your eyes.

3

For one thing, there are people who claim that shortsightedness is merely the effect of eye muscles shortened from constant strain. These guys advise you to do some sort of exercises with your eyes in order to relax those muscles and get your eyeballs round again. They usually cite anecdotal evidence in their favor, but AFAIK there is not hard evidence, so we should forget about that.

A more recent and more serious research result (and damn, I can’t find the source) is that reading is indeed a cause of shortsightedness. But it has less to do with bad light; rather, it’s all about working at very short distances (so it’s not just reading). The assumption is as follows:

When you work at very short distances, the lens of your eye cannot (or at least, does not) fully accomodate. This causes a slightly blurred image on your retina that appears as if you were longsighted. This apparently stimulates the growth of your eyeballs (through an unknown mechanism) in such a way as to correct that apparent defect, i.e. the eyeballs get longer and you really get myopic (shortsighted).

The mean thing is: The whole process could stop at that point with a slight myopia. But you will feel uncomfortable because you can’t see very well at longer distances, so you’ll see an ophthalmologist who will diagnose myopia and prescribe some glasses. With your myopia corrected, the whole process starts again, and things get worse, and worse, and…

IIRC, this idea has been confirmed in animal tests. I believe they were able to direct eyeball growth in rabbits (?) by creating apparent myopia/presbyopia using contact lenses or something. (As you can see, my memory gets weaker at his point.) I also remember that Japanese scientist who gave his children eye drops (belladonna?) through most of their childhood that made it impossible for them to focus anything close-up, so they wouldn’t get into that vicious circle. It seemed to work for them, but of course that’s no real proof that the method works. And even if it does, it doesn’t seem like a good solution to me.

IIRC, all these results were just preliminary, but the scientists involved were pretty sure anyway. There’s no real advice to draw from it, though, because you don’t want to stop your kids from reading altogether. Maybe one should try to limit the amount of reading and try to find some activity involving long distance vision as a sort of balance. Bad light does come into play as a secondary factor because it tends to worsen the accomodation performed by the lens.

Oh, and maybe I should mention that the whole process occurs mostly during adolescence, but that’s probably obvious.

4

TheIncredibleHolg:

I’ll assume you mean farsightedness and not “shortsightedness” in your post.

Other than that tiny bit of shortsightedness (hee, hee) I liked the post!

Yer pal,
Satan

5

Thanks for the detailed post, but I don’t understand how reading in low light could lead to this myopia. Surely if you are holding the book so close to your face that the image is blurred on your retina you wouldn’t actually be able to read because the image was, well, blurred. consequently you would move the book further away so that it came into focus, thus not developing the myopia in the first place?

6

I have a related question I’d like to ask:

When I was In my twenties (and ever since) I’ve noticed that when I do try to read in very low light, I simply cannot see the word which I am looking at, but the words around it are visible. But if I move my eyes to read those words, then suddenly those are the ones which I cannot see.

My suspicion is that by occasionally looking at the sun and other bright lights, I permanantly burnt out some of the rods and cones at the very center of my field of vision. My theory continues, that under normal lighting, I get enough information from the still-operating rods and cones that I really don’t have any problem at all; it is only under poor light conditions, when i need as much input as I can get, that the dead ones become noticable.

Anyone else experience anything like this?

7

My parents used to yell at me all the time for reading in the dark. I ignored them. I still have 20/20 vision, which neither of them had at my age. (OK, so that’s anecdotal evidence at best, but every li’l bit of ammo helps …)

8

Keeves, you haven’t burned anything out; your eyes are working normally.

What you are noticing is due to the way the retina is laid out, with two types of cells that have different functions. Rods can work in low light, but only sense black and white; cones do color vision, but don’t perform well in dimness.

Over most of the retina, rods and cones are about equally distributed. But the very center of the field of vision-- the spot called the “fovea”-- contains cones almost exclusively. This specialization is to give optimal color vision in daylight.

However, when you’re trying to read in the dark, the cones in your fovea have a hard time picking up any image. The rest of your retina functions well, because there are enough rods there to trigger on the low amount of light. But you instinctively shift your eyes toward the words you want to read, putting that image into your fovea and preventing yourself from seeing it clearly.

Somebody let me know if this is at all coherent; I’ve been up for too many days to be able to tell.

Laugh hard; it’s a long way to the bank.

9

Very coherent, Auraseer. Thanks a bunch!

10

It’s common for stargazers to use their peripheral vision to look at very faint stars for just that reason,
Larry

11

lvick posted 09-27-1999 01:36 PM

Yeah, I’ve noticed that helps. It’s rather disconcerting, however, to see a star in my peripheral vision only to have it disappear when I look at it directly. It sort of makes me doubt my sanity, or at least my vision.

12

Let’s not forget that other thing our parents told us would damage our eyesight.

13

Speaking of getting bad eyes in the dark, is it true that your eyes will go bad if you watch TV for a long time with the lights off?

14

don’t know anything about permanent effects on the eyes, but I know I get a bad headache if I read in low light - triggered by squinting too much, and the strain on the muscles around the eyes.

15

Satan, I did mean short- or nearsightedness, except maybe for the theory mentioned in my first paragraph, which may apply to longsightedness as well. Moonshine, I hope the following will clear up the confusion.

I’ve found a newspaper article that contains most of the info I was looking for, except for that Japanese guy. I must have read that somewhere else. First, the source: It’s from the Frankfurter Allgemeine Zeitung of Sep 24, 1997. They report on the Annual Conference of the Association for Research in Vision and Ophthalmology at Fort Lauderdale, Florida. All the interesting stuff was found by the research group of one Frank Schaeffel of the University of Tübingen, Germany. They received a Max Planck Research Award for their work, so it may not be as preliminary as I said it was.

Second, the basic mechanism: It’s all about the length of your eyeballs (height and width aren’t even mentioned). It increases from about 17 to 24 millimeters from birth until your 15th birthday. This growth occurs only at daytime, and it normally works such that there is always a sharp picture on the retina.

Third, the problem: The guys found that just about any type of vision impairment caused abnormal length growth of the eyeball. Apparently, this is due to some ‘autofocus’ mechanism in the eye itself; it works even if the eye is disconnected from the brain. The eye appears to try to correct an assumed farsightedness by growing lengthwise even at night. Dopamin seems to be involved in the process; its concentration in the retina decreases during exaggerated growth. Dopamin-like substances have inhibited myopia in animals tests.

Fourth, the cause: There any many types of vision problems that can cause this effect. In animal tests (chickens and monkeys), dispersing lenses and matted glasses work. In humans, dull corneas do the same. The most interesting case, however, is insufficient accomodation by the lens of the eye, which occurs in many people when they work at short distances. The cause is not quite clear, but it may be that their brains are less sensitive to slightly blurred vision and don’t ‘insist’ on full accomodation (which would be hard work for the lens at that distance).

(Moonshine, this seems to mean that you don’t necessarily move your book farther away because you don’t even notive that your vision is slightly blurred. Also, I assume that the effect occurs even at distances we would consider ‘normal’ for reading, but they don’t give a number. Also, I’d think there’s a trade-off between sharpness of focus and mere size of the letters that may cause you to hold the book rather close.)

Fifth, a retraction: Insufficient light may be more significant than I stated in my last post. It is another cause of improper vision that might stimulate growth of the eyeballs. Also, it seems to be especially bad to give that stimulus in the evening (because it may directly trigger additional growth for the following night, I presume; the article isn’t quite clear on that point). So reading late at night under the sheets with a flashlight is a no-no.

Sixth, the remedy: As I said previously, it’s unclear how to combat that effect. On the one hand, you want optimal vision at medium and long distances. On the other hand, retaining that slight myopia could stop the length growth of the eyeball (confirmed in animal tests). On the third hand (sorry), any type of vision impairment can cause myopia, even myopia itself (maybe depending on the degree)! At the time the article was written, they were experimenting with multifocal lenses. Dopamin, as mentioned, is another possible approach.

Seventh, other causes: There are also genetic factors involved. Kids of nearsighted parents are often born with long eyeballs. They have a probability of 60% to become myopic compared to 10% when both parents are healthy. (My personal thought is that the sensitivity of the brain discussed above should also count as a genetic factor.) But environmental factors as described above do seem to be very important: For instance, myopia in children progresses faster during school terms than vacations; orthodox jewish students who study the Bible 16 hours a day are 80% myopic; university students in Taiwan achieve a whopping 96%!

Finally, here’s the web page of the research group in question. I haven’t really looked at it yet, and I don’t have the time at the moment, so feel free to dig for yourselves: http://www.uak.medizin.uni-tuebingen.de/depii/groups/frank/

Oh, and I’m sorry for mixing up some of the details in my first post. It’s good to keep those articles in order to look things up…

16

I get it now Holg, thanks. Now I just have to find out what to do about these hairy palms.

It only hurts when I laugh.