This is about a theory that sounds stupid but I find difficult to debunk. Could the eyes’ short-term axial length response be the opposite of its long-term response?
To our new public readers: hi, I’m a resident measurement fanatic. I keep track of my eyes in multiple ways, including measuring their length with a Zeiss IOL Master to try figure out what exactly causes it to change.
This year, I haven’t been very successful at improving. Despite multiple experiments, I still could not find a useful cause-effect relationship, getting confusing results.
Looking back, also at older logs and diary entries, I’ve noticed a strange potential pattern: in the short term, my eyes often seem to react to changes in stimuli in the exact opposite way of predictions.
I know, I know, it could be random and me grasping at straws. Well, maybe, but!
This happened quite a few times, reaching back to spring 2018, when I returned from an outdoor event that lasted a few days, and measured bad distance acuity. Ever since, I’ve been confused at poor results right after weeks of cycling, or in times when I had been going to sleep earlier. And it’s not only subjective acuity. Some of the weirdest AL outliers were on the days after I returned from a vacation. Often, these bad results did not start a trend, but disappeared over time. Conversely, I sometimes had exceptionally good results after a week of heavy screen use, or just before a trend of worsening set in.
In recent weeks, since about the beginning of September, I’ve been trying to reduce consecutive screen time relative to outdoor breaks, with an emphasis on evenings. (There’s no clear starting date, but I remember looking for ideas and getting inspired by Jake’s three-hour-rule video on the 3rd, so around then. We also had an interesting chat since, where he mentioned stories of vacations that seemed to lead to worsening myopia.)
Now, have a look at the last year of my axial length measurements to see what happened next:
- The azure points are a new average, added because the EMA has a systematic lag and timing is important here. The new average is calculated by looking both backward and forward in time. (4 weeks either way, linearly decreasing weight. Newest values not mature.)
- The recent change my eyes did, circled in red, is a small but notable elongation. Subjective measurements consistently show a worsening too, and it’s quite consistent between eyes, so measurement error seems unlikely.
Long story short, it looks like being more careful about screen time made my eyes worse. What?
Some additional information:
- The hump on the right eye marked as “also weird” coincides with a period in which I was hiking more often, using a -2.25 correction, which is relatively weak for me and may leave my left eye with excessive blur, but not the right. (My left eye is more myopic, despite the AL difference.)
- The winter hump on the left eye began shortly after I stepped up my main distance glasses to -2.5, on 2020-01-10. Not sure if this is related.
It has long been suspected that changes in eye length start in the periphery and then move to central vision. This is underlined by rhesus monkey studies that showed that central vision is not important for the eyes’ adaptation.
Mechanically, I could imagine that eyes trying to begin shrinking only in the periphery could squeeze themselves from the sides, pushing central vision backwards until the change has propagated inwards, toward central vision. This would create a short-term elongation that reverts over time. I’m making this up without evidence, because it is the only plausible explanation I can think of.
A second theory that may be relevant here is that eyes adapt significantly during sleep, continuing to use whatever state of defocus they detected earlier. Long screen hours and late bedtime would muddy the eyes’ state of remembered stimulus, impeding the effectiveness of outdoor stimulus acquired earlier in the day.
Experiment & Call for Arguments
Right now, I am staying the course despite the negative response from my eyes, to test this theory.
Edit: to clarify, the biggest change I’m keeping up is being more strict on the three-hour rule: on a given day, three hours of accumulated screen-time should not be exceeded without undoing it 1:3 with quality outdoor time. So If I reach 3h, I have to be outdoors for a full hour to comply. This automatically puts a focus on evenings, since there is no quality outdoor time after dark. It’s not always possible to schedule this perfectly, so I’m aiming for high but not perfect complience and logging how well I’m keeping up.
If you have any arguments, ideas, or opinions, especially reasons why this would be wrong and I’m making a bad choice, please speak up!
As usual, I’m going to make more measurements and update this thread later, so we can see where this goes.