[Crowfossil]

Is there a DIY method of measuring a person's maximum eye pupil diameter in low light conditions? If not, when I have an eye test, would/should an opthalmologist or optometrist be able to ascertain same as part of the examination?

The reason I wish to know is that I am in my 60s and curious to know if my eyes can take full advantage of wide aperture binoculars.

Best wishes

dunk

[typo]

Dunk,

A good question, and something I've not managed to do for myself. It's relatively easy if you have pale irises to get an approximate measurement. It can take about 15 minutes or even longer as we age for the pupils to fully dilate in low light. Stand in front of a mirror (or a helpful partner) with a ruler just under the eye when it's as dark as you can manage and take a reading. If you have dark irises or need glasses (like me) it's practically impossible. If you have a suitable camera you could get a flash photo of yourself which might be easier to measure but I can't turn off the focussing lamp off on mine so that doesn't work.

Obviously an optician can do it for you by putting drops in your eye, but might need persuading as it takes more of his time, and could cause you minor problems for a while in bright light.

From the data I've found, for people in their 60's the scatter of measurements is quite large, from below 4mm to over 6mm. I'm approaching 60 and still notice an advantage of a 5.6mmEP over a 5.0mm EP, but probably as important is using a binocular with a high transmission (particularly at the blue end of the spectrum) in low light. The Zeiss FL is possibly top of the pile for this, but many cheaper Chinese made pairs with dielectric prism coatings do pretty well these days.

Good luck,

David

[Surveyor]

Hello David, dunk;

A trick you may find useful is to measure your corneal limbus diameter (limbic circle?). This is the circle of the eye where the white (sclera) joins the outside of the iris. This is usually between 11 and 14 mm and does not change with age and the average being about 12 mm. This is sometimes referred to as the white to white distance.

Since it is about the same plane as the pupil it gives somewhat better results than placing a ruler between the camera and pupil. That method usually results in a smaller than accurate result.

I have attached a jpg showing how I use my limbic diameters to proportion the pupil diameter. You can also use your IPD (if accurately known) to do double proportion to increase accuracy.

You have to be carful with the camera to make sure both eyes are the same distance from the camera (which is not the case in the attached example), otherwise the proportion to the limbus radius is more accurate.

FWIW, when I had my cataract surgery, I was told that the pupil dilation had to be greater than 5 mm or they would not do the procedure. My ophthalmologist gave me the results below of a study he was part of.



RESULTS: Two-hundred sixty-three individuals participated. For participants aged 18 to 19 years (n=6), the mean darkadapted
pupil diameter was 6.85 mm (range: 5.6 to 7.5 mm); 20 to 29 years (n=66), 7.33 mm (range: 5.7 to 8.8 mm); 30 to
39 years (n=50), 6.64 mm (range: 5.3 to 8.7 mm); 40 to 49 years (n=51), 6.15 mm (range: 4.5 to 8.2 mm); 50 to 59 years
(n=50), 5.77 mm (range: 4.4 to 7.2 mm); 60 to 69 years (n=30), 5.58 mm (range: 3.5 to 7.5 mm); 70 to 79 years (n=6), 5.17
mm (range: 4.6 to 6.0 mm); and 80 years (n=4), 4.85 mm (range: 4.1 to 5.3 mm). These values were consistent with studies
using infrared photography. The standard deviation was >0.1 mm in 10 (3.8%) participants, all of whom were younger than
55 years.

[stereotruckdriver]

Thanks interesting post!!! Bryce...

[typo]

Thanks Ron,

I'd realised the perspective errors of the ruler approach but hadn't thought of using the IPD as a reference distance. Neat. I'll have to find some way of tricking the focus on my camera.

David

[Crowfossil]

Thank you for your interesting replies. The study results are particularly interesting because the average deterioration appears to be less than i would have expected. i'd like to see and compare other results - especially if other studies have differentiated between smokers and non-smokers - because smokers' pupils deteriorate more.

Best wishes

dunk

[typo]

dunk

In a quick look through various articles on other studies and they are very much in accordance with Ron's numbers. As you noted the photopic vision is statistically a little worse in smokers but night vision in long term smokers may be 50% worse than non-smokers. This doesn't appear to be down to pupil diameter. (Though I only found a single small study on this.) Investigations appear to be focussed on retinal blood flow and carbon monoxide levels but I couldn't spot anything that appeared to explain the magnitude of the difference. I'm sure there is more information out there.

David

[typo]

Checking a few more publications it seems there are contradictory reports out there on smoking and scotopic vision.

Some report a significant impairment.
http://archive.rubicon-foundation.or...pdf?sequence=1
Other found no difference.
http://www.dtic.mil/dtic/tr/fulltext/u2/a191654.pdf

I don't know what the answer is. The anti-smoking lobby appears rather more vocal on this subject.

David

[normjackson]

You're playing Brock's signature tune David :

"They asked me how I knew,
Well I can google too,
Why can't they realise
Smoke gets in your eyes."

(OK so that could do with a bit more work).

How's it going with the anti red eye, AF assist lamp, auto focus on your camera? I've always suspected that finding workarounds for automatic features on his creations represents one of Man's greatest challenges.

[typo]

David

[Surveyor]

David,

The cameras I use now all have manual controls, including focus, but in the long ago past my first digital cameras were auto focus and I had made a small bracket out of a piece of 1/2 inch aluminum, bent in a U shape just slightly higher than the camera at the time. I drilled a 1/4" hole in one end to go between the tripod and camera and then drilled and tapped another hole in the other end, 8-32 best I remember now.

I had bent it in such a way that I could position the small machine bolt over the shutter release and tighten down just enough to get to half push so the camera would focus and hold that setting. The bracket was flimsy enough it only took a little more pressure to trigger it.

I got around the flash problem by setting the camera to flash all the time (fill flash mode), on my cameras that usually disables the auto focus lamp, but if it doesn’t, just put a piece of tape over it.

I have not tried this but think it might work. Use a rubber band and a small spacer, something like a small washer, and see if you can get to the half press position on your camera.

If you have access to a manual mode, use manual focus and set flash for the fill flash setting.

FWIW, at 6 EV, about normal residential room lighting, my eyes dilate to about 4.5mm. The 5.25 mm shown was at about 1-2 EV, enough light in my bedroom to see well enough to get around and see everything, a couple of white led lights and some digital clocks etc. Never tried fully night adapted yet.

[typo]

Ron,

I'll give those ideas a try when when I get a chance. I'd been thinking about using an industrial monochrome camera with a macro lens and IR LED illumination, (just because I have those) but that needs a computer screen to operate the camera which defeats the purpose without assistance. I'm not sure I'm likely to do any binding where I need much more than a 5mm EP pair, so It's not a priority, but I'll give it a go at some time.

Cheers,

David

[Crowfossil]

Yesterday my eyes were tested at Specsavers; the lady ophthalmologist also measured my pupil diameter as being 4mm to 4.5mm - this was as accurate as could be ascertained in the semi-darkness of the examination room and in the time available. She described the result as being," ... a little on the small size ..." but also said that,"... people with smaller pupils can focus better ..."

My ego was a bit dented after hearing her remarks and I began wondering whether I should go ahead and buy the Hawke 8x56 bins. about which I've read so many good reviews. I will probably still consider these because aperture is not everything. Then I considered my existing bins ie Fuji 10x70 and 16x70 ... and realised that the 10x70 have better edge sharpness than many other binoculars ... even if I cannot make full use of the 7mm exit pupil.

My main use for the binoculars is for astronomical observation. Given my pupil diameter result, I may now also consider a used Canon IS binocular; their relatively small exit pupils have put me off considering them previously but now hope to try some at Birdfair 2012 on 17 August.

Best wishes

dunk

[richard866945]

Surveyor, I have a web site for my optical repair business and on one page I have the figures from an Optician's measurements made in the 1930's. Would you mind if I now included the figures that you have just provided as I am sure they will be of interest to many?

[Surveyor]

Originally Posted by richard866945

Surveyor, I have a web site for my optical repair business and on one page I have the figures from an Optician's measurements made in the 1930's. Would you mind if I now included the figures that you have just provided as I am sure they will be of interest to many?

Richard;

You are welcome to use any of my figures but the table at the bottom was emailed to me by my ophthalmologist and I did not have the proper accreditation for the data.

I have got the accreditation today from him and it would probably be best to include it with the data.

The source for the data pertaining to diameter versus age came from a study:

Dark-Adapted Pupil Diameter as a Function of Age Measured with the NeurOptics Pupillometer.
J Refract Surg. 2011 Mar;27(3):202-7. doi: 10.3928/1081597X-20100511-01. Epub 2010 May 17.
Bradley JC, Bentley KC, Mughal AI, Bodhireddy H, Brown SM.

[Chosun Juan]

Originally Posted by Surveyor

The source for the data pertaining to diameter versus age came from a study:

Dark-Adapted Pupil Diameter as a Function of Age Measured with the NeurOptics Pupillometer.
J Refract Surg. 2011 Mar;27(3):202-7. doi: 10.3928/1081597X-20100511-01. Epub 2010 May 17.
Bradley JC, Bentley KC, Mughal AI, Bodhireddy H, Brown SM.

RonE,

I found the results of this study a bit of a surprise (pupil diameters larger than other 'information' I had read). In fact, none of the mean values in this study are below 4mm - even for the (4) 80 year olds! Only in the 60-69 year old age group do we even see the range start below 4mm.

I know that bright daylight can often cause the pupil to constrict down to 2.5mm or so, but I'm young enough that my normal daylight pupil is over 4mm anyway.

The seeming popularity of the 4mm EP bins, such as the ubiquitous 8x32 has always puzzled me a bit. Even in a bright landscape such as this, there's enough shade in riparian areas of open woodlands, that the ability of a larger EP to penetrate the shadows is quite useful even in summer.

I had thought that as I senesce, that I would blissfully retire to some of those lovely, lightweight 8x32 bins. Now unless I'll be traipsing around after tweety-birds into my nineties - I'm not so sure!


Chosun

[richard866945]

Thanks, Surveyor.
The entry on my web page now has the credit.