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Eye axial length changes during the day

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Eye axial length changes during the day
#1
This is not really a skeptical thread about Bates or David's method, but a general warning that even in scientific studies one has to be careful when interpreting the results of those studies. Especially if there is only one study with a specific outcome.

Many of us experience differences in visual acuity during the day. This scientific research http://www.iovs.org/content/45/1/63.long confirms this and shows that in a group of seventeen test persons, the axial length of their eyes changed during the day between 15 and 40 micrometer, which is the equivalent of 0.04 to 0.12 diopter. The maximal axial length tended to be at midday.

If you compare these values with the often quoted study http://www.ncbi.nlm.nih.gov/pubmed/20592235 which shows a decrease of optical axis length of 13 micrometer after 60 minutes of plus lens use and an increase of optical axis length of 8 micrometer with minus lens use, then at least in my opinion the amount of normal daily change of the eye axis length is of the same or even greater magnitude than the changes mentioned in the plus/minus lens use study.

We don't know the exact moment in the day the experiments took place with the plus and minus lenses, but as it is the only study I know which links optical axis length change to lens use, there can be doubt about the validity of these results looking at the normal daily changes which already occur without lens use.

Now here's a second study about daily axial length changes with the same results as the study mentioned in my previous post: http://www.iovs.org/content/49/7/2911.long

From the abstract: "Axial length was found to undergo significant diurnal variation (P = 0.0006). The mean amplitude of axial length change was 0.046 +/- 0.022 mm. The mean peak in axial length was found to occur at 1113."

A mean amplitude of 0.046 +/- 0.022 mm is the equivalent of 0.138 +/- 0.066 diopter. Also in this study the peak axial length was around midday.

So two studies show independent of each other that the axial length of the human eye fluctuates significantly during the day, and both studies show the same magnitude of change, and also the same moment of the day when the axial length is at its peak value. Compare that with only one study about the use of plus lenses with a reported change in the optical axis length significantly less than the daily change. It makes me really skeptical about that plus lens study.
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#2
And here is a third study I found which measures the effect of a +1.50 lens on the optical axis length but this time also looking at the normal daily changes which occur http://www.ncbi.nlm.nih.gov/pubmed/22971342

From the abstract: "Following the introduction of monocular myopic defocus, the daily peak in axial length occurred approximately 6 h later, [...] compared to days 1 and 3 (with no defocus). The mean amplitude (peak to trough) of change in axial length (0.030 ± 0.012 on day 1, 0.020 ± 0.010 on day 2 and 0.033 ± 0.012 mm on day 3) [...] were also significantly different between the three days (both p < 0.05). The introduction of monocular myopic defocus disrupts the daily variations in axial length and choroidal thickness of human eyes (in terms of both amplitude and timing) that return to normal the following day after removal of the defocus."

I have only quoted the text about the optical axis length, and replaced the text about choroidal thickness with [...] to make it more readable in the context of this thread. I have also marked the main conclusion in bold typeface.

So it seems that plus lenses have effect on the optical axis length of the eye because they change the amplitude and timing of the already existing daily length changes, rather than by having any significant effect by themselves. Whenever someone uses the 60 minutes plus lens study as proof that the method works for long time changes, I will suggest them to read the studies mentioned in this thread to provide them the context how to interpret that particular study.

And for those who need even more studies as background: http://www.ncbi.nlm.nih.gov/pubmed/24061153 is a study which looks both at daily changes in combination with -2.00 lens (yes, that is minus 2.00)

From the abstract
"RESULTS:
Both axial length and choroidal thickness underwent significant diurnal changes on each of the three measurement days (p < 0.0001). The introduction of monocular hyperopic defocus resulted in significant changes in the diurnal variations observed in both parameters (p < 0.05). A significant (p < 0.001) increase in the mean amplitude (peak to trough) of change in axial length (mean increase, 0.016 ± 0.005 mm) and choroidal thickness (mean increase, 0.011 ± 0.003 mm) was observed on day 2 with hyperopic defocus compared to the two "no defocus" days (days 1 and 3). At the second measurement (mean time 12:10 pm) on the day with hyperopic defocus, the eye was significantly longer by 0.012 ± 0.002 mm compared to the other two days (p < 0.05). No significant difference was observed in the average timing of the daily peaks in axial length (mean peak time 12:12 pm) and choroidal thickness (21:02 pm) over the three days.
CONCLUSIONS:
The introduction of monocular hyperopic defocus resulted in a significant increase in the amplitude of the diurnal change in axial length and choroidal thickness that returned to normal the following day after removal of the blur stimulus."

Now this is interesting. A minus lens increases the daily amplitude of axial length significantly, whereas the previously mentioned study showed that a plus lens decreased the daily amplitude significantly. But this is not a permanent effect and only visible at a peak moment which is around midday for minus lenses and six hours later for plus lenses. So instead of pushing or pulling the optical axis length continuously in one specific direction, using plus or minus lenses changes the amplitude and timing of the daily axis length changes. The specific moment of measurement in the day therefore greatly influences the outcome of that measurement and may therefore well be the reason for the optical axis length changes mentioned in study http://www.ncbi.nlm.nih.gov/pubmed/20592235
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#3
(01-02-2015, 03:46 PM)bloobi Wrote: And here is a third study I found which measures the effect of a +1.50 lens on the optical axis length but this time also looking at the normal daily changes which occur http://www.ncbi.nlm.nih.gov/pubmed/22971342

From the abstract: "Following the introduction of monocular myopic defocus, the daily peak in axial length occurred approximately 6 h later, [...] compared to days 1 and 3 (with no defocus). The mean amplitude (peak to trough) of change in axial length (0.030 ± 0.012 on day 1, 0.020 ± 0.010 on day 2 and 0.033 ± 0.012 mm on day 3) [...] were also significantly different between the three days (both p < 0.05). The introduction of monocular myopic defocus disrupts the daily variations in axial length and choroidal thickness of human eyes (in terms of both amplitude and timing) that return to normal the following day after removal of the defocus."

I have only quoted the text about the optical axis length, and replaced the text about choroidal thickness with [...] to make it more readable in the context of this thread. I have also marked the main conclusion in bold typeface.

So it seems that plus lenses have effect on the optical axis length of the eye because they change the amplitude and timing of the already existing daily length changes, rather than by having any significant effect by themselves. Whenever someone uses the 60 minutes plus lens study as proof that the method works for long time changes, I will suggest them to read the studies mentioned in this thread to provide them the context how to interpret that particular study.

And for those who need even more studies as background: http://www.ncbi.nlm.nih.gov/pubmed/24061153 is a study which looks both at daily changes in combination with -2.00 lens (yes, that is minus 2.00)

From the abstract
"RESULTS:
Both axial length and choroidal thickness underwent significant diurnal changes on each of the three measurement days (p < 0.0001). The introduction of monocular hyperopic defocus resulted in significant changes in the diurnal variations observed in both parameters (p < 0.05). A significant (p < 0.001) increase in the mean amplitude (peak to trough) of change in axial length (mean increase, 0.016 ± 0.005 mm) and choroidal thickness (mean increase, 0.011 ± 0.003 mm) was observed on day 2 with hyperopic defocus compared to the two "no defocus" days (days 1 and 3). At the second measurement (mean time 12:10 pm) on the day with hyperopic defocus, the eye was significantly longer by 0.012 ± 0.002 mm compared to the other two days (p < 0.05). No significant difference was observed in the average timing of the daily peaks in axial length (mean peak time 12:12 pm) and choroidal thickness (21:02 pm) over the three days.
CONCLUSIONS:
The introduction of monocular hyperopic defocus resulted in a significant increase in the amplitude of the diurnal change in axial length and choroidal thickness that returned to normal the following day after removal of the blur stimulus."

Now this is interesting. A minus lens increases the daily amplitude of axial length significantly, whereas the previously mentioned study showed that a plus lens decreased the daily amplitude significantly. But this is not a permanent effect and only visible at a peak moment which is around midday for minus lenses and six hours later for plus lenses. So instead of pushing or pulling the optical axis length continuously in one specific direction, using plus or minus lenses changes the amplitude and timing of the daily axis length changes. The specific moment of measurement in the day therefore greatly influences the outcome of that measurement and may therefore well be the reason for the optical axis length changes mentioned in study http://www.ncbi.nlm.nih.gov/pubmed/20592235

Nice find,that blows away most of Bates theory.
Where are all of the naysayers on this.
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#4
Hi bifocal, you can read it as you want, but the maximum length of the studies was three days and in all the studies the effect of plus and minus lenses is gone after 24 hours not using them. The conclusion that these studies "blow away most of Bates theory" is not what I concluded from it.

My conclusion based on these studies is that plus and minus lenses DO cause effects on the axis length of the eye, but that it in those studies only lasts during the use of those lenses, not afterwards. This does not say anything about the long term effect of using lenses, nor invalidates any other method or theory like Bates' method.
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