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Thread: Eyewear and Night Driving

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    Eyewear and Night Driving

    On another thread the topic drifted (imagine that) from SV free form to night driving. Pete Hanlin requested a new thread to cover this issue and the great discussion that ensued.

    See thread here, starting on page 2: http://www.optiboard.com/forums/show...192#post294192

    The question of what to do with patients who have a difficulty driving at night arose after Pete made this comment:

    Quote Originally Posted by Pete Hanlin View Post
    ... That brings me to fad product that just really causes me to seethe- namely, yellow tinted "night driving" lenses. Basically, placing ANY tint in front of the eye will reduce contrast sensitivity (because less light is making it to the retina). Anyone who could theoretically benefit from a yellow tint (e.g., someone with advancing cataracts) probably shouldn't be driving at night anyway. I would discourage practitioners from prescribing any kind of tinted lens for night driving (at least in the Dallas / Ft. Worth area :^).
    So Pete, here is your new thread. And to everyone else, is there anything we can do to help patients who do have trouble driving at night?

    Sharpstick

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    First tell them to clean the windshield inside and out. You have no idea how much this helps except just after you have done so.
    While it is true that no tint transmitts light better than air, I do have couriosity about whether a light yellow might not: 1) filter out light that one cannot precieve and therefor use at night, such as colors. 2) Possibly activate the rods which all one uses to see with at night.
    O.K. Pete, I'm ready.

    Chip

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    Glare reduction at nite is complicated

    My 30 some years spent in lab/manufacturing/ technical training had given me a false sense of real issues with night driving. My following 6 years as Ophthalmic dispensing (80% elderly) has shown a whole "new light".
    We deal with pre/post cataract surgery, retinal issues, and an amazing amount of pigment bleaching through lack of sun protection. These issues point to more than one effect, and I have found no tint helping any of our local issues. If glasses must be worn at night, only addition of AR coating seems to help.
    Yes, looking at the white line while oncoming vehicles are passing should be standard driving skills, but glare also is equally distracting from highly reflective roadsigns. Too often I see recommendations of blue-blocking (yellow) tints, but strongly disagree that they really help in extreme low light.

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    I still have a couple of questions. I have a few younger latent hyperopes with A/R who complain of increased brightness while driving with their new glasses.

    1) Although A/R reduces reflected glare, it inadvertantly increases the brightness of direct light from 6.5%-11% depending on the material through improved transmission. Is a lens with a low amount of tint and A/R better than a clear lens without A/R? with the same total net transmission.

    2) The newer Xenon bulbs produce more blue light than stnd bulbs and a larger pupil size at night could increase the scattering effect of blue light (since its entering the eye at increased angles), so with Xenon bulbs people with blue light sensitivity could benifit from a yellow tint in theory. Has anyone done a study on the effects of blue light and pupil size?

    3) what about the option of backside only A/R (allowing the front of the lens to naturally reduce transmission 7 - 10%)? you would still get about 70% of the advantage of A/R I believe.

    4) Has anyone done a study on pupil size with or without A/R at night? The increased glare of not having A/R could in theory reduce pupil size.

    5) more of my patients with night driving issues are not necessarily old, but they do tend to be hyperopes. We have reduce problems with myopes by over correcting for night vision. Is there anything we can do with the RX of younger hyperopes?

    6) I suspect some of these patients have irregular astigmatism that is only revealed with a larger pupil size. Is there any way to detect this without the expense of corneal topography?

    7) could an Rx based on a wet refraction help these people? because their larger pupil size matches closer to what they see at night.

    Just questions in my head. Your answers are appreciated.

    Sharpstick

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    Great topic! Thanks for devoting a new thread to this discussion so it doesn't get lost.

    I've been toying around with this topic for a while now. I'll never forget reading in a textbook (Systems, I think) that a 10% tint combined with reflected light off the windshield can take you from 20/20 to 20/40 at night. Therefore, I'm very hesitant to recommend any tint for driving at night, and the yellow tint thing used to make me want to scream.

    However, I have come into contact with several patients lately who've basically self-prescribed this method and say that they see so poorly at night while driving that they're much better off with the yellow. Are we to just let these folks suffer? (Most of these folks have had corrective eye surgery) Are we to tell them just to stay off the roads at night? What of the patient who swears they help? Several of my patients have found yellow "fit-over" type sunglasses to wear at night.
    If a 10% tint is a big deal, why isn't high-index w/o AR, which causes almost as much light to be lost?

    And finally, should all patients under 18 be wearing polycarbonate???:cheers::cheers:

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    Eyes eastward... Uilleann's Avatar
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    Night driving (or flying as some of us do as well) will always present with a unique set of variables for us to consider. The first thing to look at I believe would be the actual measured transmittance of the windscreen material. Some high end vehicles actually use multi treated surfaces (not a true A/R, but a similar concept I believe - blue, purple and gold/amber IIRC color casts), and some do not. There are differences between these and a standard laminated glass I expect. I wonder if the NTHSA would have any data regarding the same?

    As to the tint question, it strikes me in much the same way as the Oakley crowd - fancy and effective marketing. And if enough people watch the late night infomercials, then it *must* be true right? The placebo effect may well be at play I would venture to guess. Not unlike my bagpipe playing - if I just want it bad enough...eventually they WILL play in tune! :shiner:

    In the case for a backside only A/R lens, this is what we commonly do on suns. But in these cases, we're still trying to reduce the amount of light into the eye. Pupils will always be smaller in sunlight conditions, and thus any marginal uncorrected astigmatism minimalized as well correct? However in a low light/night situation, then I would think we again would want to maintain as much integrity of focus throughout the entire optical system as possible - and that would be A/R both sides.

    As an interesting aside to the original question that prompted this thread, would vision gain a greater single benefit from a digital/free-form design? Or A/R lenses? Or is the combination of the two even greater than the sum of it's parts?

    I, for one, would be very interested in the measurable effects of the same base lens with A/R in both cases, but a traditionally vs. digitally surfaced design, when used specifically at night. Perhaps using a tinted lens of some form as well just to mix it up. I wonder, if a patient was asked to close their eyes, and was given a random tint cast, how many would notice the actual color cast of a 10% tint. I bet far more would guess incorrectly that would get it right. I also wonder how many would be able to tell the difference between A/R lenses vs. non vs. tinted etc. If there was a means of offering the different choices unknown to the pt., much as is done during refraction, we may find some very interesting results.

    All the best!

    Brian~

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    Lots of questions, little answers available

    I too am becoming more curious with additional research papers read. Seeing data suggesting the dilated eye in low light can actually perceive better accuity with blue light as it concentrates more in the area of the "rods" would tell me a blue filter may help. I doubt it, but is that the reason for blue emmiting headlamps?
    There is an abudance of research papers on these topics, but only more concepts to consider.

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    ATO Member HarryChiling's Avatar
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    Night myopia is in part caused by the distance objects not having enough contrast so the eye focuses by way of accommodation to a intermediate or near state. This accommodation causes the eye a gain in myopia of 1 to 4 Diopters, it is going to effect the young more than it will the old.

    A slight yellow tint will only further reduce contrast therefore further degrading the image, AR helps when a lens is supposed to be there by way of increasing the transmission as well as reducing the ghost images. Of course with better transmission is good.

    Also consider that the fovea is made up of cones which are suited for daylight conditions and provide the sharpest VA, where as rods are better suited for night time lighting conditions and provide less VA. The fovea has "0" rods, and is the part of the eye that provides the best VA, so 20/20 at night may not even be a good indicator as the level of acuity may not be there in night conditions combine that with the fact that it takes about 30 minutes to adapt to dark conditions. When a patient is exposed to very bright conditions the rods are essentially bleached, when they are put in dark environment the rods slowly gain the biochemical rhodopsin. In a night driving situation if the patient were to stare directly into bright oncoming headlights their vision afterwords would be slightly less dark adapted which makes for an interesting situation.

    Third the cornea flattens further from the center and when we have to consider the pupil being larger then we do have to consider spherical aberration of the eye and it's effects on the prescription, this is not to be confused with spherical aberration in a lens, but can be thought of as the aberration in a lens system comprised of the cornea.

    My best suggestion, a good pair of sunglasses in the day time, this will reduce the level of bleaching and provide the wearer with a quicker dark adaption period, it may not even be a bad idea to incorporate anywhere from -0.50 to -0.75D of additional power in a separate pair for night driving.
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    Eyes eastward... Uilleann's Avatar
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    In the subject of headlamp design and spectral emission, there is a mass of information that seems to be flooding the market. There is a huge range of color cast and intensity between: HID, xenon, halogen, and an almost endless string of 'colored bulbs' currently available. There is also a sharp debate over whether or not many of the 'new' technology bulbs are in fact "more blue" as opposed to just "less yellow". There is also a small, but very vocal portion of the population who decries HID lamps as "too bright" and that they cause unsafe driving conditions for other drivers due to their "excessive amount of glare". While it is true that the lumens emitted from an HID lamp exceed that possible from a standard halogen, it seems the biggest complaint is that some drivers don't like the much more defined horizontal cut-off of HID style lenses. As an oncoming vehicle moves over the uneven road surface, some drivers complain they are blinded by the "flashing" effect of HID lamps and lens structures.

    Interestingly however, almost every HID design focuses far more light on the road, and far less at oncoming traffic. However, regardless of the increased efficiency of this style of lighting, it is still one of the most vocal complaints we hear pertaining to night driving conditions.

    For a cataract patient, what are the most easily and least scattered visible frequencies in a low light situation? In a normally functioning, non color-deficient retina, it is a greenish-yellow cast most easily picked up by our rod cells. Whereas the cones will pick up the entire visible spectrum - they are still most sensitive in the mid portion of the visible spectral range (unless I'm remembering my EM training backwards or something here...which could be the case!) which again correlates to yellows, oranges and greens. Reds take a bit more 'oompf' from the brain to process cleanly, and blue/violet requires the most amount of effort to resolve cleanly - hence the 'fuzzy' appearance of black light bulbs.

    I would still think that first and foremost, we should concentrate on maintaining the integrity of final focus as much as we possibly can, as that will undoubtedly afford a much better of contrast sensitivity and clarity for a patient. I would still think (logically I hope!) that a high quality A/R lens, coupled with a digital/free-form lens design regardless of SV or progressive, would be the best means to achieve this.

    I'm dubious, as it sounds several others are as well, on the purported efficacy of tinted lenses in a reduced light or night driving scenario.

    Bri~

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    Quote Originally Posted by HarryChiling View Post
    it may not even be a bad idea to incorporate anywhere from -0.50 to -0.75D of additional power in a separate pair for night driving.
    ...with a prescription stated as such, right?

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    Quote Originally Posted by Uilleann View Post
    I would still think that first and foremost, we should concentrate on maintaining the integrity of final focus as much as we possibly can, as that will undoubtedly afford a much better of contrast sensitivity and clarity for a patient. I would still think (logically I hope!) that a high quality A/R lens, coupled with a digital/free-form lens design regardless of SV or progressive, would be the best means to achieve this.

    I'm dubious, as it sounds several others are as well, on the purported efficacy of tinted lenses in a reduced light or night driving scenario.

    Bri~
    1000% agree here.

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    sub specie aeternitatis Pete Hanlin's Avatar
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    Too often I see recommendations of blue-blocking (yellow) tints, but strongly disagree that they really help in extreme low light.

    You have hit the nail on the head. The problem with tints (of any kind) at night is they reduce light transmission in a situation where light is at a premium.

    Night time driving presents two simultaneous challenges:
    1.) Oncoming headlights are bright enough to cause temporary night blindness due to "bleaching" of the retina.
    The "blue dot" in the middle of your vision after a camera flash is caused by temporary "bleaching" of the chemicals in your retina which trigger the sensation of light. Unfortunately, as we age these chemicals take longer to replenish- so elderly drivers will be most prone to temporary night blindness from headlights.

    2.) Very low levels of illumination reduce contrast sensitivity, so its harder to discern detail at night.
    Again, this issue becomes larger as we age- because the eye transmits less and less light to the retina (a 60 year old retina receives only 1/3 the light it did when the patient was 20). Furthermore, when driving an eyeglass wearer is losing even more light to the windshield and eyewear.

    Our clinical site has a driving simulator set-up that incorporates a windshield. Due to our ongoing discussion, I took some time to look at the windshield yesterday and was suprised to notice how dark it looks (see the attached picture). I asked why we use a tinted windshield for the studies, and was informed the windshield in the picture is not tinted (other than at the top). The reduction in transmission comes from the various layers (windshields are laminated for safety). We measured the transmission reduction with a spot meter and a photometer and concluded a standard windshield reduces transmission by about 20%!

    So, with that in mind, let's address the questions from Sharpstick...
    1) Although A/R reduces reflected glare, it inadvertantly increases the brightness of direct light from 6.5%-11% depending on the material through improved transmission. Is a lens with a low amount of tint and A/R better than a clear lens without A/R? with the same total net transmission.
    Given the windshield is already blocking 20% light, it would seem AR with no tint is the best solution. However, in some conditions a tinted AR lens would approximate the transmission of a non tinted, non AR lens.

    2.) The newer Xenon bulbs produce more blue light than stnd bulbs and a larger pupil size at night could increase the scattering effect of blue light (since its entering the eye at increased angles), so with Xenon bulbs people with blue light sensitivity could benifit from a yellow tint in theory. Has anyone done a study on the effects of blue light and pupil size?
    A study conducted by Renault indicated Xenon lights were actually preferred by senior drivers- although the extra brightness was not sufficient to restore vision to the level of younger drivers. Of course, this is Xenon lamps on the senior's car- and the question is the effect of Xenon lamps on an oncoming car.
    http://www-nrd.nhtsa.dot.gov/pdf/Esv/esv16/98S2P23.PDF
    Regarding oncoming Xenons, I believe Xenons are more annoying because they are brighter- not because they are "blue" (even though blue light is scattered within the eye, a halogen light of the same luminance is going to produce glare that is just as annoying).

    3) what about the option of backside only A/R (allowing the front of the lens to naturally reduce transmission 7 - 10%)? you would still get about 70% of the advantage of A/R I believe.
    Besides increasing transmission, the advantage of AR is reduction of ghost images. I would recommend AR on both sides for night driving applications. An elderly driver is losing 20% of an image's light at the windshield, then 60-70% of the remaining light is lost intra-ocularly. Oncoming headlights are annoying- but taking away additional transmission to reduce the headlight glare is going to result in further reduction of vision even when headlights are not present.

    4) Has anyone done a study on pupil size with or without A/R at night? The increased glare of not having A/R could in theory reduce pupil size.
    Pupil size actually decreases as we age (although of course the pupils still enlarge at night). I am not aware of a study on pupil size (correlated to AR), but I don't believe the 5-8% of light transmission gained with AR is going to affect pupil size one way or the other.

    5) More of my patients with night driving issues are not necessarily old, but they do tend to be hyperopes. We have reduce problems with myopes by over correcting for night vision. Is there anything we can do with the RX of younger hyperopes?
    The eye does become up to 0.50 diopters more myopic at night. A study at Goteborg University demonstrated increasing minus correction by 0.50 diopters could resolve "night myopia," but both subjects in the study were myopes. I would want to confirm, but I believe a hyerope (who retains accommodative ability- which would be the case with your younger patients) would benefit from 0.50 less plus correction at night as well.

    6) I suspect some of these patients have irregular astigmatism that is only revealed with a larger pupil size. Is there any way to detect this without the expense of corneal topography?
    Good question- topography would have been my suggestion. I seem to recall there is a handheld device that acts kind of like a "manual topographer." It shines concentric circles on the cornea so the practitioner can manually assess the shape of the cornea. You also might be able to use fluorosciene (sp?) and a RGP to note patterns (but CLs are definitely not my area of expertise, so this last comment is purely grasping at straws ;^).

    7) Could an Rx based on a wet refraction help these people? because their larger pupil size matches closer to what they see at night.
    Another good question, but I don't think a wet refraction will help, because the lower orders of the Rx is unlikely to change. There ARE drops that will keep the pupil size smaller (I've had several ophthalmologists discuss it with me when I talk about my post-LASIK observations... more than one has indicated they use it- think its called Alphagan-A or something with truck drivers who suffer from halos at night). Would have to check with a practitioner about the specific drops.

    At the end of the day (pun intended), if a senior is having real and serious difficulty with oncoming glare at night, it might be time to consider hanging up the driving gloves at night. Yeah, I know that's going to be a really popular conversation out there in the real world, but let's face it- I'm 41 and don't do all the things I did when I was 21. Due to the 2 simultaneous challenges described above, any attempt to increase comfort in the presence of oncoming glare is going to reduce vision at all other times.

    So, for seniors the best scenario involves clear lenses with AR. For younger drivers, clear lenses with perhaps up to -0.50 power to account for dark induced myopia. It is important to note that tinted lenses do not INCREASE contrast sensitivity for ANY patient. At best, they may decrease discomfort in the presence of oncoming glare- but the price is reduced vision in the absence of oncoming glare.

    Hope some of this information has been helpful or interesting!
    Pete
    Attached Thumbnails Attached Thumbnails windshield.jpg  

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Quote Originally Posted by HarryChiling View Post
    Night myopia is in part caused by the distance objects not having enough contrast so the eye focuses by way of accommodation to a intermediate or near state. This accommodation causes the eye a gain in myopia of 1 to 4 Diopters, it is going to effect the young more than it will the old.


    ....the cornea flattens further from the center and when we have to consider the pupil being larger then we do have to consider spherical aberration of the eye and it's effects on the prescription.

    (and this is a further contributor to the totality of night myopia, along with the Purkinje effect)

    My best suggestion, a good pair of sunglasses in the day time, this will reduce the level of bleaching and provide the wearer with a quicker dark adaption period, it may not even be a bad idea to incorporate anywhere from -0.50 to -0.75D of additional power in a separate pair for night driving.
    Excellent suggestions, Harry. In astronomy, we empirically derived the amount of night myopia using spherical flippers. Alternatively, in my experience with binoculars, one could, as a rule of thumb, take approx 60% of the minus dioptric from an IF binoc and add it to the eyewear for night driving/star gazing.

    FWIW

    Barry

    Another contributor is that many Rxs leave the eye undercorrected (overplussed). So, comparatively, some seniors may "experience" the *effect* of night myopia, even when their adds are +2.75.

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    What's up? drk's Avatar
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    Quote Originally Posted by Barry Santini View Post
    one could, as a rule of thumb, take approx 60% of the minus dioptric from an IF binoc and add it to the eyewear for night driving/star gazing.
    But again, I'm here to stress that you need the license to prescribe to do this!

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    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by drk View Post
    But again, I'm here to stress that you need the license to prescribe to do this!
    Without question, this is a physiological aspect of the prescription so is to me without question in the ODs domain, sorry if it didn't come across that way it was implied.


    Quote Originally Posted by Uillean
    it is a greenish-yellow cast most easily picked up by our rod cells.
    Actually greenish-blue, 510nm being the optimal, this could also correlate to the reason why the Xenon or bluer bulbs seem to be so bothersome at night they may bleach the rods quicker.

    Quote Originally Posted by Pete Hanlin
    Again, this issue becomes larger as we age- because the eye transmits less and less light to the retina (a 60 year old retina receives only 1/3 the light it did when the patient was 20). Furthermore, when driving an eyeglass wearer is losing even more light to the windshield and eyewear.

    Glad you brought that up even before the windsheild or glasses, the loss to the naked eye is 4% at the cornea (no you can't AR the eye's :bbg: ), then another 50% due to the the ocular media, not to mention of that light reaching the retina only about 20% will be absorbed by the rhodopsin. If we were to start with 100 quanta of light 4% loss at the cornea leaves us with 96 quanta and then a 50% loss of that leaves us with 48 quanta then 20% being absorbed by the rods would leave us with 9.6 quanta of light. Now when you factor in the windsheild and the glasses it all starts to make sense a bit more.

    BTW great topic.
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    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by drk View Post
    ...with a prescription stated as such, right?
    My lab provides me with a printout that say's it's the compensated prescription. :p:bbg: (OK, sorry man I was just fooling with you on that one) :cheers:
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    What's up? drk's Avatar
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    Don't get me wrong; some of you know multiple times what many practicing ODs do regarding optics and vision.

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    I too have had patients tell me they prefer a tint at night, although I recommend only clear eyewear with A/R. This is long before the marketing hype Pete mentioned.

    Does anyone on this forum have difficulty driving at night themselves? Unfortunately I see really well in the dark (I actually prefer to drive at night because I can see so well). I am really interested in finding out if a digitally processed SV would be better than a standard stock lens.

    Why do some patients feel better with a yellow (or crux or pink) tint when driving at night? It it was just reduced transmission, another color such as gray 10% would do just as well to reduce the brightness. I have sent 2 patients out with tint samples (with the Drs permission) and one seemed to prefer Persimmon, the other Crux. So I wonder if photophobia is present only at night, or if blue light affects some people more.

    Also, is Coma abberation increased at night? or with increased pupil size?

    Sharpstick

    Quote Originally Posted by EyeFitWell View Post
    ....However, I have come into contact with several patients lately who've basically self-prescribed this method and say that they see so poorly at night while driving that they're much better off with the yellow. Are we to just let these folks suffer? ....What of the patient who swears they help? Several of my patients have found yellow "fit-over" type sunglasses to wear at night.
    ...If a 10% tint is a big deal, why isn't high-index w/o AR, which causes almost as much light to be lost?
    :cheers:
    Last edited by sharpstick777; 04-24-2009 at 04:24 PM.

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    Pupillary Reaction Times by Age

    One theory I was playing with was that pupillary reaction times could decrease with age, but I found a study that elimated this:

    http://www.ncbi.nlm.nih.gov/pubmed/1...gdbfrom=pubmed

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    sub specie aeternitatis Pete Hanlin's Avatar
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    However, I have come into contact with several patients lately who've basically self-prescribed this method and say that they see so poorly at night while driving that they're much better off with the yellow.
    I've met a few people who claim they drive better when slightly intoxicated, too... :)

    I would guess if yellow is making that much of a difference then there is something within the eye that is really scattering light. The USAF conducted a large study some years ago which concluded a healthy human visual system is not precise enough to benefit from colored filters (which is why the study recommended sunwear for pilots should be N-15). Today, the USAF allows pilots to wear colored filters (the thought being, if the pilot thinks a yellow tint gives him an advantage, that in itself is an advantage). So, the yellow filter effect is either psychological in nature for these patients- or there is a defect within the eye that is creating a situation where selective filtering may help somewhat.

    However, if the patient has a condition that makes driving at night so challenging that the only solution is the use of a yellow filter which reduces the amount of light entering the eye, that patient needs to seriously consider whether s/he should be driving at night.

    I'm really not a super rule following kind of guy, so I don't want to be hypocritical- however, operating a car involves responsibility. Driving with impairments (whether intoxication, under the influence of prescription drugs, or having a visual challenge) is just a bad idea.

    Also, is Coma abberation increased at night? or with increased pupil size?
    The level of coma in the eye (or an eyeglass lens) does not physically increase. However, when the lens stop (pupil) becomes larger perception of coma will increase. This is pretty much true of all aberrations. With the smallest possible lens stop (i.e., a pinhole), aberrations are eliminated because the only ray entering the eye is not refracted.

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    Good point Harry, I had not thought of that at all...

    Quote Originally Posted by HarryChiling View Post
    Third the cornea flattens further from the center and when we have to consider the pupil being larger then we do have to consider spherical aberration of the eye and it's effects on the prescription,
    Has anyone actually tried this? I would be curious to see if the theory holds in the real world, because it could be a real help if it works. I would also be curious to see if a patient benifits from just -.25 change.

    Quote Originally Posted by HarryChiling View Post
    it may not even be a bad idea to incorporate anywhere from -0.50 to -0.75D of additional power in a separate pair for night driving.
    Poly non-adapts in low RX's still pose a little bit of mystery to us. The math does not add up, and they have a variety of symptoms, but we all know its a real problem sometimes. They are just more sensitive to chromatic abberation than the mean. I wonder if these patients with night vision issues are also sensitive to poly.
    Last edited by sharpstick777; 04-24-2009 at 09:09 PM.

  22. #22
    ATO Member HarryChiling's Avatar
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    Quote Originally Posted by sharpstick777 View Post
    Good point Harry, I had not thought of that at all...



    Has anyone actually tried this? I would be curious to see if the theory holds in the real world, because it could be a real help if it works. I would also be curious to see if a patient benifits from just -.25 change.



    Poly non-adapts in low RX's still pose a little bit of mystery to us. The math does not add up, and they have a variety of symptoms, but we all know its a real problem sometimes. They are just more sensitive to chromatic abberation than the mean. I wonder if these patients with night vision issues are also sensitive to poly.
    As Pete mentioned:

    Quote Originally Posted by Pete Hanlin
    The level of coma in the eye (or an eyeglass lens) does not physically increase. However, when the lens stop (pupil) becomes larger perception of coma will increase. This is pretty much true of all aberrations. With the smallest possible lens stop (i.e., a pinhole), aberrations are eliminated because the only ray entering the eye is not refracted.
    In the case of night myopia and the pupil the size of the pupil won't contribute to the aberrations in the lens but the aberrations on the corneal surface. So to correct or compensate for this would require aberrometry or some sort of additional information that relates to the cornea so that the rate of flattening can be taken into considerations when designing the lens. Even if that were so again the accommodative shift from distance 20 ft to a point more intermediate to near due to lack of contrast would change the incident light upon the system which would make any daytime calculations for reducing aberrations slightly off.

    As for sensitivity to poly, the sensitivity is chromatic aberration the rest of the aberrations as monochromatic, in a situation like night driving the level of light available makes chromatic aberration fairly tolerable except with headlights and other bright light sources where the contrast to the source and the background are extreme. I would think that chromatic aberration at night would be less of an issue then during the day.
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    In the early '90's when I first started in Optical I was told by many people men had an advantage driving at night because we had more rods, and women had more cones. However, I have never found a study or research material to back that claim.

    Is there a study that proves this or is this an optical myth?

    (I was hoping such a study uncovered other things)

    Thanks,

    Sharpstick

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    sub specie aeternitatis Pete Hanlin's Avatar
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    As for sensitivity to poly, the sensitivity is chromatic aberration the rest of the aberrations as monochromatic, in a situation like night driving the level of light available makes chromatic aberration fairly tolerable except with headlights and other bright light sources where the contrast to the source and the background are extreme. I would think that chromatic aberration at night would be less of an issue then during the day.

    I agree, and would add that "sensitivity to polycarbonate" is usually due to surface quality rather than an attribute of polycarbonate.

    For noticeable chromatic aberration to occur, you have to have considerable prism- and therefore considerable dioptric power. When I was still in quality management at Essilor, I actually had a practitioner send several pair of polycarbonate lenses with minimal Rx (<0.50) for evaluation (with the claim that patients were complaining of "chromatic aberration"). However, low power lenses do not produce perceivable levels of chromatic aberration (since there is minimal refraction of light)- turned out there were polishing swirls in the lenses (invisible to the naked eye, but they show up quite nicely under an arc lamp). Polycarbonate is perhaps the most challenging material your lab surfaces- so process variables in the lab (e.g, polish temperature, generator removal rates, etc.) will show up on polycarbonate lenses first.

    Additionally, polycarbonate and 1.67 materials have very similar abbe values- so if a patient has problems in poly- but is okay in 1.67- the original problem wasn't with the poly itself.

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    Quote Originally Posted by Pete Hanlin View Post
    For noticeable chromatic aberration to occur, you have to have considerable prism- and therefore considerable dioptric power..
    Although this holds true MOST of the time I have a patient that was able to detect purple/yellow shift in poly at -1.25 D. Another patient in a +.75 sphere who started as a poly non-adapt so we went through 1.60 and Trivex (a rare Trivex non-adapt) before CR-39 finally worked (frame, lens design, BC, and power were all the same).

    Quote Originally Posted by Pete Hanlin View Post
    turned out there were polishing swirls in the lenses (invisible to the naked eye, but they show up quite nicely under an arc lamp).
    If it took an Xenon or Carbon arc lamp (arc lights power searchlights) to detect the swirls we are looking at least 500 x 1000 times the lumens of ambient light for you to see the same defect. These swirls must have been in the sub-hundreths of a diopter level of distortion to require that much light to detect them. Again something that defies the math and explanation. Although you discovered a defect, you didn't discover why this person was uniquely affected by it.

    I was trying to be brief earlier but ended up mis speaking. The comparison is that Poly for a multitude of reasons (bi-fringence, coating issues, swirls, abbe issues) stresses the visual systems of some of our patients resulting in a myriad of symptoms that all fall under the category of "Poly Non-adapt". These all occur in lower RX's on occaision, lower than what the math tell's us they "should", and in symptoms that rule out swirls (the occaisional color shift, or temporal blur).

    We don't dismiss these poly patients as nut cases, nor do we send them down the road explaining there is nothing we can do. They have not heard anything bad about poly in the media (some don't even know they are wearing poly) so they are not affected by advertising by the Trivex department at PPG.

    I think there is a danger in applying a median of optical behavior to all patients, and dismissing the one's that don't conform to our mathematical precepts. We don't do this with poly (I hope not) and I hope we don't do it with our patients with night driving issues. We just need more tools in our tool box.

    Patients are self perscribing tinted lenses (which despite the science seems to help them), and if this is bad, we need to get them other options.

    Sharpstick

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