Could dry eyes be causing this sudden drop in distance vision?

In the last two weeks or so, I had the biggest drop in focus distance (centimeters to blur on the computer) since I began logging last spring:

Image: my log, in diopters relative to the horizon. The green dots are calculated from my focus distance to my computer screen, with about 1 dpt undercorrection. Light blue dots are from autorefractors, orange are manual tests by optometrists (with cylinder ignored).

Because of the lack of progress since September, I’ve been troubleshooting before the drop began, doing a few tweaks on my computer and reading setup. But I find it hard to believe that this drop was caused by a few small changes. Brightness when measuring doesn’t seem to be the cause either. And I don’t think I’m doing anything that could cause this much ciliary muscle spasm. So either my eyes are rapidly worsening for unknown reasons, or there’s some other factor involved.

So I have a suspicion: could this be due to the very dry indoor air when it’s freezing outside? I noticed that my eyes now often feel (and look) dry, and indoor humidity is low, below 35% is normal these days. The drop happened roughly when temperatures dropped below freezing, which means heaters stay on 24/7. Also, if I measure a few minutes after getting up, my acuity is almost as good as before. But after just a little while in a warm room or in front of a screen, it goes down significantly.

There are some articles that describe how dry eyes reduce distance vision, so it could contribute. But is the effect really that strong on a week-to-week basis? Or am I on the wrong track here? Gotta say, I’m a little worried, because as the graph shows, nothing like this has happened since I started.

Have any of you had had similar experiences? Thanks in advance for any input!


The tear film is incredibly important for vision. And I wouldn’t be surprised if that was exactly what your problem is. When my eyes are dry I can’t see anything, then when I feel them being properly lubricated everything clears up. I also made a post about the reason I may not be able to active focus on the car, which I suspected was due to dry cabin air, and Jake said he used to experience the same thing.


It"s easy to find out: Just put some ( or a lot) bowls of water on your heaters. Sounds like you have a tool to measure indoor humidity, right? So, wait for ‘normal summer indoor humidity’ and check your eyes.
Do you drink enough? This may contribute to dry eyes as well (some people just forget to drink, especially when it’s cold).
As your :eyes: seem to be doing well early in the morning, it could very well be the case.


@Blake That’s reassuring to hear! With those stories, it seems much more likely that I got it right.

@Tii_Chen This experiment sounds like fun and something I’d love to do, but in this case, it’s not very practical… the room has some cold walls that condense moisture. It had to be renovated after last winter, because blackboards had blocked the air movement to an outside-facing wall, and all the wall area behind them was overgrown. So, apart from it being hard to get humidity high in winter, I also don’t want to risk another fungus farm. :sweat_smile: But even without a perfect way to test this, It looks like we’re onto the culprit. :grinning:

I’m drinking enough, always got a glass of water around. In the past, I was one of these people not drinking enough, so it’s good you’re reminding people!

Anyway, good to know I’m not the only one with this effect. I’ll keep an eye on the weather and do some extra measurements if there’s a warmer and more humid day.


Hmm. Well, look at the bright side – I consider it a great thing if the eyes become more even.

Seems like a different cause though. My fast drop happened quite symmetrically in both eyes. Even how much they jumped up or down between measurements was similar.

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Absolutely, yes. But you should (eventually) be able to tell if dryness is the cause, or if it’s something else.

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Dry eyes may well be part of the problem. I have eye drops with hyaluronic acid in my desk drawer that help a bit whenever my eyes feel dry. But on top of that, less light due to pretty dreary weather during the last weeks may play a role, too. Your log started in April when the summer began. Now we have the darker months of the year to “weather through” :wink: . For me, I don´t expect any significant progress until March…



  • I measured axial length, and the result isn’t good at all. Estimating something like 50-70 µm longer for both eyes than my previous measurement in November – by far the highest readings since I started tracking AL in September. So the best-guess estimate is a loss of over 0.1 dpt from the eyes’ length.
  • This morning, I took extra precautions against dry eys when measuring. That brought the measurements back to better levels, undoing most of the steep drop, but they remained on the low side compared to the logs of recent months.
  • With my newly installed ~10000 lumen of additional, high-quality (CRI-95) lighting, I can mitigate lighting effects relatively well. I don’t think poor lighting when measuring is as big a factor as the two above.

So, it looks like two main factors: dryness of the cornea, plus longer eyes.

Of course, the latter is worrying. I don’t think I have done anything that’s expected to cause elongation; I’m doing all reading and computer use at the edge of blur, just as I did during times of improvement, and even though I don’t get as much quality outdoor time as in summer, I should have gotten at least a little bit of distance stimulus. So I don’t understand where the elongation is coming from.

Now, I can’t tell whether the AL change is from scleral sctructure, choroid, or something else like blood pressure, so it’s still possible that this will go away with the weather or time. But considering that Jake’s standard improvement rate would predict a significant decrease after these months, overall, this still isn’t looking good.

I’ll start a troubleshooting thread more focused on the axial part once I have the facts straight. But feel free to leave any comments on the topic here already, since the original question seems answered. Even if not in the way I would have liked. :neutral_face:

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How does one measure one’s axial length?

Interferometry; you need the appropriate medical device. Usually, that is the Zeiss IOL Master.

If you don’t have a special way to get access to one, you could try getting a deal from the people who plan cataract surgeries. They should have the means to measure AL. Either way, it’ll be pricey; it’s not a device you’d normally find at your optometrist.

I’m a fanatic, so I found a way to make it happen. Might make a separate thread on that soon. I really want to know whether long-term axial shortening is real, and if/how I can make it work consistently, so I’m working on making the best vision log I can. But that’s not useful if I can’t keep improving, so now I gotta check if I made any mistakes that caused this worsening.


I also think that it may be the weather outside. I experience this very often, a drop in cm, when it’s getting darker outside or if there are a couple of days in series without sun. But also dry eyes can be a factor. So it maybe both.
Strange, that your AL measurements are going up. Since I started with EM I measured every while and then my eyes with the autorefractor and in the beginning the diopters increased. I thought that this may be some measurement-errors, but perhaps this is something else. I’m looking forward to your AL measurements! Seems to be very interesting.


I am wondering whether eye is able “on a temporary basis” to change length, thus somehow during your measurement to result in a longer AL.

Considering the other parameters you have isolated, we have either the environment to effect both eyes really to make them longer, despite all precautions, or eyes as living mechanisms respond to something.

I would speculate that your drop in cm is caused by dryness, I experience it too, especially in airconditioned environment.
And the AL has not increased but during measurement, the eyes are responding to a stimulus, maybe to the machine. Morning vision acuity would be my basis…

On the other hand, my approach could be foolish.

Anyway, I am trying to be patient until spring/summer comes, and take into consideration only my measurements on balcony in bright light, similar to summer mornings… Anything else makes me depressive…

Kind regards


try watering your eyes in a natural way and then immediately do the measurement

Yes, in principle, the choroid can change thickness within an hour or so. However, it doesn’t look like that’s it from control measurements. At least within two days, the results are extremely reproducible. Looks like my choroid is either maxed out or not deciding to change thickness.

It is in part, but if I had to guess which effect is bigger, I’d opt for the axial component at this point. Dryness certainly plays a role, and I guess the two together made the drop as extreme as it looks in the plot. But even with lots of blinking and going to a humid room before measuring, I have a hard time reaching just the typical range of last month.

Simple math is also a thing. 50 µm is expected to cost me over 0.13 dpt; that’s a decent chunk of the drop right there.

Hmm, IMO doesn’t seem too likely. First, the choroid shouldn’t change that quickly. Measurement takes just a few minutes. If anything, it would need to have already changed before measuring.

But that would be weird too, because I’ve taken multiple measurements with this exact machine since September, and I’ve repeated the new measurement a whole four times, most recently just before writing this. There’s simply a jump between the old and new measurements, but otherwise, they’re very reproducible. Now, it could be that the machine decalibrated in storage within the last month, because there’s one little check I couldn’t do (comparing to another machine wasn’t possible this time, because that one had been sold), but let’s be real… the device has been ultra-precise for many years, what are the chances it goes bonkers now?

If I’m honest, I was never that good in determining the edge of blur. If use any possible method to catch the best moment of clarity I can get, I don’t think the result will make for a fair comparison with the earlier samples. After all, surely there were dry days before, yet I didn’t have such severe drops. And from the results that have accrued since I made this thread, it looks like I have to accept that dryness is only part of the answer, and elongation makes up for the rest.

Now that the situation is clearer, I’ll start a new thread in a moment, focused on the AL measurements and details that may have played a role.

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I don’t see why your axial length would increase if you are constantly creating myopic de-focus. Hopefully you figure it out soon. I would assume it has something to do with the measurement itself.

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Could it have happened when you increased your correction to that high point not too long ago?

If not, I have more ideas.

Biometric tests are indeed frought with error, and can be hard to reproduce accurately. It might be fluctuating like the stock market.

I continued the regression topic with better data in my thread on my IOL Master and troubleshooting.

The elongation does not at all look like measurement error. I have now logged nine measurements per eye after the drop, and not a single one of them lies in the range of earlier measurements. This is highly significant. And the machine shows no signs of a changed bias, or any bias at all. The IOL Master isn’t like an autorefractor; I can repeat measurements under various conditions and everything stays consistent.

To me, it looks like the drop happened quite suddenly after I started correcting for too much blur, especially indoors. It appeared almost simultaneously with various pressure-like sensations on the eye sockets that correlated with improvement in the past. I’m quite sure I didn’t cause excessive accommodation though. It’s also weird that the drop seemed so sudden.

This doesn’t make a lot of sense to me. If you have more ideas, please tell me. But maybe we should continue in the other thread; this one is about the dry eye theory, which is more or less addressed now. (It plays a role, but there’s a more important issue at play here.)

Are you saying you added back more correction right before you noticed the drop?

@Blake Yes, however, this level of correction and setup had been stable at an earlier time and roughly the same focus distance readings.

The sequence was: noticed no progress whatsoever, so I reverted computer setup from experiment that may have accidentally increased blur levels. This involved more correction, but also a change in geometry that counters some of that. This current setup is what I used during times of improvement. Two days later, I also reverted indoor and some outdoor uses of glasses from a similar higher-blur experiment; three days after that (on the next measurement) the drop was already pretty obvious.

As far as the numbers go, if anything, I should have corrected a problem in the parameters, not introduced one. It looks like my eyes responded, but in a counter-intuitive way. I’m not sure if that is random, and whether it indicates that a given change was good or bad.

I’ll update the other thread with more data eventually, but right now, I caught a cold, so that might be messing things up.