20 replies to this topic

[FrankRyanJr]

I never knew what 'night myopia' was until one of our club members did a talk about it. After testing my eyes at night with a set of diopter flippers and getting a separate pair of 'observing glasses', it's made an incredible difference.

This shows what I'm talking about and how you can test your eyes yourself and get a pair of glasses cheaply. 

https://youtu.be/SCpk3I9qqbc

 

Edited by FrankRyanJr, 09 January 2023 - 08:29 PM.

[siriusandthepup]

I did this a few years back. My Ophthalmologist let me borrow a couple pair of flippers to evaluate after my cataract surgery on both eyes. I test 20/20 (20/15 actual) daytime and while fine to drive, even at night, without glasses - I can tell the night myopia is present.

 

I determined that about -0.5 to -0.75 worked best for me. I had a super nice set of glasses made up with this prescription (told my eye doctor my results and he wrote the script for me). Sky looks great at night unaided eye, but put on the night glasses - pinpoint!

[yuzameh]

Had to look that up.  It seems I haven't got night myopia, but I have certainly noticed that needing reading glasses is not the ony factor of old age, I can't see as well in the dark (when I can find some actual dark, it is quite rare nowadays) as I used to, even with the reading glasses on.  I used to be able to stand at the scope in the old low pressure sodium days and still be able to read black on white charts.  Now even in these horrid LED days I can struggle without a handheld light source.

[rocco13]

Had to look that up.  It seems I haven't got night myopia, but I have certainly noticed that needing reading glasses is not the ony factor of old age, I can't see as well in the dark (when I can find some actual dark, it is quite rare nowadays) as I used to, even with the reading glasses on.  I used to be able to stand at the scope in the old low pressure sodium days and still be able to read black on white charts.  Now even in these horrid LED days I can struggle without a handheld light source.

Amen to that. I now require reading glasses not only when looking at charts but also when using the Celestron hand controller. That red light display never gets bright enough for me to read it without glasses! (I've never had an easy time with red light reading, even when younger.)

 

Don't even get me started on trying to decipher the tinier and tinier icons that are in newer vehicles. Got a new company truck and one early morning trying to figure out the defroster icon (or so I thought) I didn't realize until after I got to work that I had turned on the heated seats instead. I need the 'large print edition' of everything, including hardware!

[EmDrive2821]

Night Myopia:  Some Basic Points & How Correct For It.

Night Myopia is a complex subject that not surprisingly was originally recognized by astronomers. The first person to publish on night myopia was the English astronomer Nevil Maskelyne (1732-1811), who in 1758 reported that he observed increased myopia in dim illumination (1).  Lord Rayleigh (1842-1919) independently wrote about it in 1883, describing how a -1.0 diopter (D) lens improved his visual acuity in a dimly lit room (2).

There are many hypotheses that contribute to our understanding of night myopia, but no single hypothesis entirely explains the phenomenon.  Chromatic aberration, spherical aberration and accommodation have all been reported as contributory.  The many postulated physiological optics concepts are not the purpose of this writing.  I will limit the presentation to a more pragmatic discussion with an application to Astronomy.

 

The Basics 

The basic unifying point is that stimuli usually experienced in the night environment place the human eye in a more myopic state compared to that experienced in daylight.  It is a condition in which the myopic refractive error of the eye increases or the hyperopic refractive error decreases at low luminance. Subjects with neutralized refractive error under photopic conditions may exhibit this myopic shift as they experience the reduced luminance of a scotopic environment.

 

In the young adult human eye under scotopic (dark) conditions, this myopic shift has been reported to be as much as 4.0 diopters, with an average of 1.0 to 1.5 diopters (3). Values vary from study to study because the research methods and protocols vary widely.

 

Most of the published quantitative data for night myopia was generated by subjective refraction, similar to the typical testing one experiences during an eye exam. Unfortunately, there is no specific test for night myopia.  The amount of power required for correction varies between patients.  Its determination must be subjectively empirically established (trial and error, what is better, “1 or 2…”)  This measurement can be accomplished by the provider or the patient with some guidance.  Trial lenses make this easy, especially if they are mounted in flippers.

 

Flippers

 

Compare vision with your best correction alone & with the addition of trial lenses. 

1. Obtain a set of loose trial lenses or flippers ranging from-0.25 or -0.50 to -2.00 diopters.
2. Under dark conditions, fixate on a Star field, planet, the Moon or run trials with all of them.
3. Compare the resolution with an up to date pair of glasses alone and again with -0.50 D  trial lenses or flippers over the glasses.
4. Continue trials increasing the handheld trial lens power until you find the appropriate power for optimum vision.  This can be done unilaterally and/or bilaterally.
5. Record which flipper or trial lenses provided the best vision in tandem with your glasses.
6. The new spectacle Rx correcting for night myopia will be the combined powers of the original glasses and the trial lenses that provided the best subjective vision in the above test.
7. It would be sensible to permit the provider to re-run some of the tests for confirmation.

A few important points.

Remember that night myopia does not affect viewing through a telescope or binoculars.  This applies to Naked Eye Viewing.  Age is a risk factor.  The younger one is, the greater the night myopia is likely to be (4). Pseudophakic (post cataract) patients can also exhibit night myopia (5).

 

Night Myopia & Night Blindness 

Night Myopia should not be confused with Nyctalopia.  While night myopia occurs in normal healthy patients, nyctalopia is always associated with some form of pathological process.  Night myopia will always respond nicely to the appropriate refractive correction. Nyctalopia will not respond to the addition of minus power.  As we age, some will be affected by both Night Myopia and Nyctalopia.  Your eye care provider will be able to help you sort things out.

 

Gary

 

Reference

1. Levene, John R.  “Nevil Maskelyne, F. R. S., and the discovery of Night Myopia.”  The Royal Society Journal of the History of Science.   Volume 20, Issue 1.   Published: 01 June 1965https://doi.org/10.1098/rsnr.1965.0006
2. Lord Rayleigh. “On the invisibility of small objects in a bad light.”   Proceedings of the Cambridge Philosophical Society 1883;4:324. [Google Scholar]
3. Owens, D. A., H. W. Leibowitz,  “Night Myopia: Cause and a Possible Basis for Amelioration”, Am. J. Option., 53: 709-716, 1976.
4. Lee, Hark-Jun & Kim, Chang-Sik.   “Study on the Night Myopia of Refraction.”  Journal of Korean Ophthalmic Optics Society.  Vol. 13, Issue 1.  P. 107-112.  2008.
5. Shinichi Aoshima, Toyofumi Nagata & Ikuo Wanatabe. “The Simulation of Night Myopia in Pseudophakic Eyes.”  Japanese Journal of Ophthalmology.  Vol. 44, Issue 6, Nov–Dec 2000, P. 691-692.

 

Glossary

 

Accommodation - the focusing process of the vertebrate eye that adjusts the optical power to maintain a clear focus on an object as its distance from the eye changes.
Flippers - hand held lens mounts that permit the user to look through trial lenses bilaterally for multiple purposes.

Myopic Shift - a change in the refractive status of an individual where they become more myopic or less hyperopic.

Nyctalopia - Night Blindness, always with some form of pathological process involved. This includes a very wide range of diseases.

Photopic - relating to or denoting vision in daylight or other bright light, believed to involve chiefly the cones of the retina.
Pseudophakia - The presence of an Intraocular lens implant after the natural crystalline lens has been removed as with cataract surgery.
Scotopic - relating to or denoting vision in dim light, believed to involve chiefly the rods of the retina.

Edited by EmDrive2821, 11 January 2023 - 02:30 PM.

[Cotts]

When I had both of my lenses replaced in 2017 due to cataracts I recognized the opportunity to 'tune up' my eyesight to account for Night Myopia.  I talked the surgeon about it and he did his due diligent research- he had heard about night myopia but I was his first ever patient to talk about it.  I wanted PERFECT vision, without glasses, when my eyes were fully dark adapted.  So he chose my lenses accordingly.

 

My daytime vision is absolutely 40/20 when I wear a pair of simple 'readers' from the drug store which are 1.00 diopter.  It is outstanding!!

 

When I am observing and dark adapted (or driving at night, even) I just remove the glasses and the Night Myopia takes over.  Absolutely pinpoint stars!! 

 

Reading a book or on the computer I use 2.25 diopter glasses and I have pair of 3.75 diopter for when I need to do really close-up work..

 

Dave

[Joshua Roth]

Very excited to see this thread. More background and history (with nice S&T graphics) can be found here. Clear skies! - JR

[Jon Isaacs]

 

There are many hypotheses that contribute to our understanding of night myopia, but no single hypothesis entirely explains the phenomenon. Chromatic aberration, spherical aberration and accommodation have all been reported as contributory. The many postulated physiological optics concepts are not the purpose of this writing. I will limit the presentation to a more pragmatic discussion with an application to Astronomy.

 

Very interesting stuff.

 

I figured that the reduction in depth of focus at large exit pupils must be part of the equation.  The depth of focus with a 7 mm pupil is 1/12 that of a 2 mm pupil. 

 

Jon

[Tom Masterson]

Interesting stuff that brings a thought to mind. I'm wondering, if this is indeed a fairly common condition, might there be an evolutionary reason for it. Is it benificial in some way, or is it simply that the visual system doesn't need distance acuity in low light situations so it unoptimises distant resolution at night? Like what's up close in the dark is more important from a survival standpoint. Or at night, being myopic might aid in reading facial cues in close social situations - again a benificial trait as we evolved into more socialy complex creatures. Is it prevalent in other species of great apes, or other social animals? Since there's much less data coming in to the visual system in the dark, is it more important to see what you might stumble over, than to be able to see sharply into the distance where there's more visual noise or lack of contrast? If so it may be a way of reducing the load on the visual system when there's little light. Could that offloading free up sensory processing power for other senses such as hearing?

 

It may be a byproduct of an imperfect visual system, or rather it may be something that offers some advantage however small in survival. In modern times we may be thinking it as an shortcoming because it diviates from how we think the visual system should behave at night based, on how we use it during the day. Commonly being myopic is seen as a deficit in daily life, what if nature knows better and we evolved it for a reason?

 

Dunno. Just wondering. I could be way off here, but that's what comes to mind.

[Redbetter]

I bought a set of night time myopia flippers a few years ago.  The one odd thing with them was that the diopter was printed in light red ink, which was invisible with a red light and didn't have enough contrast to read in dark sky--so I wrote the diopter on them with a black sharpie.

 

Anyway, I have some mild daytime myopia when focusing for infinity, and what I found was I had nearly the same level of myopia at night, within a quarter of a diopter of that measured at the eye doc.  -0.5 has been the sweet spot although -0.25 and -0.75 are helpful too.   I use them when doing NELM checks at dark sites.

[EmDrive2821]

Interesting thought brought up by Redbetter.  Does Empty Field Myopia = Night Myopia ?   I will look around on the web for any information.

 

Gary

[Joshua Roth]

I bought a set of night time myopia flippers a few years ago.  The one odd thing with them was that the diopter was printed in light red ink, which was invisible with a red light and didn't have enough contrast to read in dark sky--so I wrote the diopter on them with a black sharpie.

 

Anyway, I have some mild daytime myopia when focusing for infinity, and what I found was I had nearly the same level of myopia at night, within a quarter of a diopter of that measured at the eye doc.  -0.5 has been the sweet spot although -0.25 and -0.75 are helpful too.   I use them when doing NELM checks at dark sites.

 

I too found myself scratching my head at the faint red labels! But I decided the bug was a feature and labeled my set A, B, C, D in black sharpie -- so my test subjects could look through them free of bias and then I could tell them their offset

[Joshua Roth]

I bought a set of night time myopia flippers a few years ago.  The one odd thing with them was that the diopter was printed in light red ink, which was invisible with a red light and didn't have enough contrast to read in dark sky--so I wrote the diopter on them with a black sharpie.

 

Anyway, I have some mild daytime myopia when focusing for infinity, and what I found was I had nearly the same level of myopia at night, within a quarter of a diopter of that measured at the eye doc.  -0.5 has been the sweet spot although -0.25 and -0.75 are helpful too.   I use them when doing NELM checks at dark sites.

 

I have been told that practicing eyecare providers don't usually optimize Rx for infinity at daytime, but rather a useful intermediate distance, say for driving ... and so it was not entirely surprising to them that one would need a 'bump' of extra 'minus sphere' (myopia correction) to see stars at 'infinity' ... even if you did not exhibit an additional shift due to the darkness (whatever the cause).

[munirocks]

"Night myopia" sounds like a misdiagnosis /misnomer to me.

 

During the daytime your pupil closes down and your eye behaves more like a pinhole camera, hardly needing any lens at all to make a reasonable image.

 

Under dim night conditions your pupil opens up and your eye uses/needs more of the lens to achieve focus, so any defects in the lens will then make themselves more obvious, whether that defect is astimatism, hyperopia, or myopia. This is a simple well-known aspect of human vision. 

 

If you think that "night myopia" falls outside of this explanation, please explain it to me.

[Joshua Roth]

For sure, astigmatism is a much bigger deal when dilated. But there is a tendency, on average, for people to become (among other things) more myopic in the dark than by daylight, regardless of their nominal daytime Rx. That said, there is a lot of scatter, with some people evincing a negligable shift.

[Jon Isaacs]

"Night myopia" sounds like a misdiagnosis /misnomer to me.

 

During the daytime your pupil closes down and your eye behaves more like a pinhole camera, hardly needing any lens at all to make a reasonable image.

 

Under dim night conditions your pupil opens up and your eye uses/needs more of the lens to achieve focus, so any defects in the lens will then make themselves more obvious, whether that defect is astimatism, hyperopia, or myopia. This is a simple well-known aspect of human vision. 

 

If you think that "night myopia" falls outside of this explanation, please explain it to me.

 

i had suggested that in an earlier post but I think there is more to it than that. I have presbyopia, no accommodation,.  i know that reading my tablet during the day or in the bed at night, my 3.25 diopter reading glasses are ideal.  If my eyes are full dark adapted, then I need to move the tablet significantly further back to have it in focus.. 

 

Jon

[Tony Flanders]

"Night myopia" sounds like a misdiagnosis /misnomer to me.

 

During the daytime your pupil closes down and your eye behaves more like a pinhole camera, hardly needing any lens at all to make a reasonable image.

 

Under dim night conditions your pupil opens up and your eye uses/needs more of the lens to achieve focus, so any defects in the lens will then make themselves more obvious, whether that defect is astimatism, hyperopia, or myopia. This is a simple well-known aspect of human vision. 

 

If you think that "night myopia" falls outside of this explanation, please explain it to me.

No, if that were all there were to it, then the glasses that produced the sharpest possible nighttime view would also produce the sharpest possible daytime view. But in fact that's not true -- at least not for many people.

 

At the moment my optimal nighttime prescription seems to be not very different from my optimal daytime prescription. But a decade ago, when my eyes were significantly more myopic than they are now, I bought a special pair of astronomy glasses that were 3/4 diopter stronger than my daytime glasses, and they enabled me to see stars at least a quarter magnitude fainter than I could see with my daytime glasses. Yet it was exceedingly uncomfortable to wear my astronomy glasses during the daytime because my vision was severely over-corrected.

 

Having said that, one of the many not-quite-adequate explanations of night myopia is spherical aberration -- the central part of your eye lens has a different focal length from the peripheral part of the lens. By the reasoning it would make sense that the optimal compromise focal length would vary depending how much of your eye lens is stopped off by the iris. And no doubt that is, in fact, part of the explanation for night myopia. I forget the reasoning that shows that it can't be the sole explanation.

[Redbetter]

 

Having said that, one of the many not-quite-adequate explanations of night myopia is spherical aberration -- the central part of your eye lens has a different focal length from the peripheral part of the lens. By the reasoning it would make sense that the optimal compromise focal length would vary depending how much of your eye lens is stopped off by the iris. And no doubt that is, in fact, part of the explanation for night myopia. I forget the reasoning that shows that it can't be the sole explanation.

 

Yes, that is what I gathered would be the primary physical reason for such a difference.  I don't see much difference in the level of myopia night to day for my eyes, so it is interesting to me that some folks experience a very large difference in diopter.

 

This is an area where those who have had cataract lens replacement could provide helpful data for evaluating what is happening.  My understanding is that the replacement is fixed focus and should be properly figured for the eye at some distance.  So the question is, with a properly figured lens does the person still experience significantly different levels of night and daytime myopia?  If a person had substantial night myopia before (vs. daytime) and the effect went away with the lens replacement, then it would confirm that the problem was primarily in the lens rather than elsewhere in the eye.  

 

Of course, the pupil diameter varies somewhat with age as well, so as we age and our dilated pupil becomes smaller (at least on average), this would likely reduce the observed difference in night to day myopia correction.  At the same time our accommodation is becoming less and less...

[Jon Isaacs]

Yes, that is what I gathered would be the primary physical reason for such a difference.  I don't see much difference in the level of myopia night to day for my eyes, so it is interesting to me that some folks experience a very large difference in diopter.

 

This is an area where those who have had cataract lens replacement could provide helpful data for evaluating what is happening.  My understanding is that the replacement is fixed focus and should be properly figured for the eye at some distance.  So the question is, with a properly figured lens does the person still experience significantly different levels of night and daytime myopia?  If a person had substantial night myopia before (vs. daytime) and the effect went away with the lens replacement, then it would confirm that the problem was primarily in the lens rather than elsewhere in the eye.  

 

Of course, the pupil diameter varies somewhat with age as well, so as we age and our dilated pupil becomes smaller (at least on average), this would likely reduce the observed difference in night to day myopia correction.  At the same time our accommodation is becoming less and less...

 

Red:

 

While I have not yet had cataract surgery, my eyes are essentially fixed focus.  My dark adapted pupil is relatively large,

 

My normal computer glasses are 1.5 diopters, my tablet and normal reading glasses are 3.25-3.5 diopters. For reading my tablet under dark skies, I use 4.5 diopter readers. They allow me to read the tablet at about the same distance as I do normally with the screen at nearly full brightness.

 

The blind test is this:

 

If I accidentally go outside with the 3.25 diopter readers, I have difficulty reading the tablet at it's normal settings with it's red screen. I wait a while to see if I can see it better with better dark adaptation but when that doesn't happen I then realize that to get best focus, I have hold the tablet father away from me, close to 12 inches. 

 

Under bright lighting, at that distance, I cannot read text because it's out of focus. This is the critical observation, something is causing a shift in my myopia at night. 

 

Once I realize I have the wrong glasses, I go inside, swap them out and all is well.

 

Jon

[FrankRyanJr]

I have been told that practicing eyecare providers don't usually optimize Rx for infinity at daytime, but rather a useful intermediate distance, say for driving ... and so it was not entirely surprising to them that one would need a 'bump' of extra 'minus sphere' (myopia correction) to see stars at 'infinity' ... even if you did not exhibit an additional shift due to the darkness (whatever the cause).

This was exactly the same reaction I got from my optometrist last month when I was having my eye exam! She basically said something to the effect of 
'Well of course you would, the eye chart is only on the other side of the room, you're talking about a distance of infinity'' 
Seems so obvious when it's pointed out to you. She had told me there were patients that had asked for an extra ;little bump for a separate pair of glasses for night driving, which is something that she said she'd only do for long time patients she knew well. Now if she could only get rid of my astigmatism...  
 

[Joshua Roth]

I sometimes wish I could have elective eye lens replacement to optimize myself for stargazing, with replacement lenses upping my blue sensitivity while banishing myopia and astigmatism.