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Home Forums General Ergonomics Topics Recommended visual distance for computer monitors larger than 17″

This topic contains 15 replies, has 6 voices, and was last updated by  GCWesq 12 years, 10 months ago.

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  • #37199

    sandra2714
    Participant

    Hello Everyone
    I know this has been discussed somewhat in previous discussions, but I am looking for some specific information with regards to recommended distances for computers that are larger. I am seeing larger LCD monitors in a typical workstation anywhere from 17"-21". Does the recommended distance for computers that are larger change? If so how is this calculated?
    Thank you
    Sandra Burke

    #38821

    [private user]
    Participant

    Sandra,

    Are those the size of the monitors or the working distances?

    The "scientific" way to determine optimal viewing distance is called the "one-third rule". Have them put up on the screen the material they’re normally viewing. Have them move back as far away from the screen as they can and still see the text clearly. Measure that distance. Take one-third of it and that is their optimum viewing distance. However, if they come up with a viewing distance of less than 24", I tell them to enlarge the font.

    Jeff
    Dr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

    #38824

    sandra2714
    Participant

    Thank you very much for the information. 17-21" is actually the size of the monitors. 

    You had mentioned that if the viewing distance is less than 24" you make them increase the font. Is there a specific size you recommend or do you just recaluculate until the distance is greater than 24"?

    I do have one more question. I often do some muscle posture balancing tests to provide a visual demonstration to people that many of us possess some imbalances in our bodies that make us more susceptible to MSDs and we need to minimize factors that create these both in our work and off work activities. For example I will test right lateral neck flexion and I will measure with my fingers the distance between their ear lobe and neckand do the same thing on the other side and most people will have a difference of 1-2 finger widths which demonstrates a slight neck postural imbalance. Is there a quick and easy test for the eyes? 

    I find that most people neglect their eyes and although I often talk about vision breaks and how important they are if I had some sort of test in my bags of tricks to emphasize this importance I think it would provide more power to my preaching. Any suggestions would be greatly appreciated. 

    Thanks Sandra

    #38832

    [private user]
    Participant

    Table 17 from the CSA-Z412 Guideline on office ergonomics (2005) gives a guide to the relationship between character height and viewing distance.

    #38843

    GCWesq
    Participant

    Jeff, that method for determining monitor distance presumably only applies to people without glasses or contacts.  Do you have a suggestion for people with corrective lenses as to where in their focal field the screen should be (centre, front, back)?

    While on the subject,  do you think there is a need to have an ergonomist or similar professional involved in deciding the optimal viewing distance and the preferred lens type (bifocal, etc) for a person having lenses prescribed?  I have heard of instances where the client tells the optometrist what they do and the optometrist makes up the prescription according to that.  The result has not been satisfactory because some factors were not taken into account.

    #38982

    [private user]
    Participant

    Geoff,

    I have to disagree- someone wearing contacts or glasses can easily do this procedure. However, it is limited to those under 40 years old (and not wearing any multifocal correction). I always recommend that the screen be centered and just below straight-ahead eye gaze level (so they can just look over the top of the display when looking straight ahead).

    The problem with getting the right prescription lies both with the employee (as patient) and their doctor. The employee rarely knows the correct viewing distance (they don’t measure before going into the eye exam) so they’re just guessing. Then there are eyecare professionals (sad to say) that have no clue about how to prescribe for computer users. Standard bifocals never work (of course, there may be the rare exception) and standard progressive lenses (no-line bifocals) rarely work (the intermediate viewing area is too narrow). I teach doctors how to prescribe "occupational progressives", which allow for clear near and intermediate viewing with lenses on. In addition, the doctor rarely asks about other environemental factors (mostly lighting) that might be contributing to the issues that the employee has.

    Hope this helps
    Jeff

    Dr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

    #38983

    GCWesq
    Participant

    Thanks Jeff.

    I was under the impression that corrective lenses had a limited depth of focus, so I couldn’t see how it would be possible to use the one-third rule – if you focused as far back as you could, and then moved in two-thirds of that distance, I thought you would then have to be out of focus. I take it you are saying that is not so. Does that apply for any types of lenses (you have excluded multifocals, so does that mean there is a type of lens for which this would not apply)?

    What do you suggest for over-40’s and for people with multifocals?

     

    With regard to employee and doctor – you have highlighted the issue a bit by mentioning that you teach doctors how to prescribe "occupational progressives".  The problem we have then is that there are presumably doctors who have not had that tuition, so neither they nor the ‘patient’ is able to properly determine what is needed.  That is the situation I was alluding to, where there may be a need for someone, an ergonomist, for example, to provide assistance.  The issue arose here because we help people set up their workstations, and naturally that includes screen distance.  That then raises the issue of what to do with people who wear corrective lenses.  Some people seem to have the wrong lenses, as well, and we want to be able to tell them and their doctor what sort of lenses to get (by defining the viewing distance and range that would best suit them).

    Geoff

    Mark Dohrmann & Partners Pty Ltd

     

    #38875

    [private user]
    Participant

    Geoff,

    Yes, you are right- lenses do have a limited depth of focus. However, I was talking about the human eye, not just the lenses. The lenses are designed to correct refractive errors so that the light focuses where it should at the back of the eye (retina). However, we have a system for accommodating to varying distances closer than 20 feet; this "accommodative" system gives us the flexibility to see broader ranges- whether the lenses are on the eye or not. This is the system that changes as we age- and by the time we hit our 40’s, we notice that the ability to see within arm’s length is reduced- called presbyopia.

    For those over 40, we need to use the lenses to help them with that lack of accommodation. That is where the viewing distances become critical- we strive to enable all viewing distances to be clear but that often can’t be accomplished with just one pair of glasses/contacts. Thus we ask to see where the computer display sits so we can adjust the power of the glasses to see that distance.

    The doctors-to-be in school do not receive much education on computer vision issues; and often nor do the practicing doctors. I’m assuming you’re somewhere in the UK, so I don’t have many answers about the education process there (contact me personally for a referral). I have my hands full trying to get the US docs on-board with asking the right questions to prescribe appropriately for computer users.

    JeffDr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

    #38876

    [private user]
    Participant

    Jeff,

    If you are "always" setting the top of the screen just below straight-ahead  eye gaze level with these larger monitors, do you find that employee’s report more neck discomfort because the bottom part of the viewing screen is much lower than if that same rule is applied with a smaller screen?  That seems to be the case for one of my client where their standard monitor size is 24"-30" and multiple screens.  That top of the screen rule has not worked well for me when the employee prefers to keep the screen flat.  Do you keep the screen flat or do you set the screen with tilting the bottom of the screen upward to allow the focus distance to remain the same when viewing from the top or the bottom?  Another question I have is some of the users I work with prefers a portrait configuration over a traditional landscape configuration?  Do you have any guidelines that you follow?

    Appreciate your input and anyone else who replies?

    #38857

    sandra2714
    Participant

    Hello
    I would be very interested in this topic. I have not noticed an increase in neck discomfort, however that could be because my monitors are usually around the 17-20" range so maybe this has not been an issue for me as of yet. 

    I do have increased reportes of glare when the monitor is not perpendicular to the desk however. So although the neck isn’t an issue the reports of eye strain and headaches increases slightly particularly if there is lighting overhead of the work area.  

    Awesome question!
    Thanks Sandra

    #38986

    [private user]
    Participant

    Dear it4ot (the best I can guess at your name….)

    First, by "always" I don’t mean that this is a rule set in stone. It’s a starting point. I realize that many people have physical issues and other considerations regarding monitor position. In viewing this from an "eye" point of view, it’s the best starting point.

    In my experience, the people who do not like this posture often lower their monitors without adjusting the angle of the screen. Recall that we do not read hard copy with the book in a vertical plane either- nor should we do so with the display. The top should be angled back about 10-15 degrees. For larger monitors, this will also allow the bottom of the screen to be viewed fully. In general, the face of the screen should be perpendicular to the line of sight at the center of the screen.

    I haven’t encountered many portrait users but can imagine that the same guidelines might apply. With this configuration, however, a further viewing distance can allow a more vertical alignment of the screen.

    JeffDr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

    #38987

    [private user]
    Participant

    Sandra,

    I run into that quite often as well. The reason being that lights in the workplace are most often designed with empty rooms and even illumination (usually due to local codes). This does not allow optimal placement of overhead lighting to highlight the necessary areas and low-light the computer areas. This will most often lead to glare off the screen when the display is tilted. There are several options to resolve this- including turning off overhead lighting, rearranging the workstation, and even using an umbrella over the chair (behind the employee) if necessary (only recommended that once!!) But, whatever works!!

    Jeff

    Dr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

    #38988

    GCWesq
    Participant

    Things are changing these days with the larger screens, aren’t they. This may be another case where technology is ahead of ergonomics.  You would probably be aware that traditionally (if we have been at this long enough to have traditions), the recommended viewing angle is between about 10 and 20 degrees below horizontal (depending on whom you listen to).  This is based on the most relaxed viewing posture.  (On this basis, for one thing, that might mean that the top of the monitor is placed below eye level if it has a large screen and the user places it well back, although that probably applies more to wide screens, as normal-shaped screens get higher as they get wider, and that would compensate.)

    I think that looking up is probably worse than looking down, as far as neck strain goes (within the range we are talking about, others may like to comment here), so it is probably better to minimise upward looking, even if it means looking further down than is desirable, at times.  If the screen content could be arranged such that information at the top is that which is only viewed occasionally, a good compromise could be reached.

    This raises the issue of the need to be aware of where the person is looking most. If one part of the screen, or one screen, receives most attention, that spot should be in the best position.  If there is screen stacking – one on top of another – it may be advisable to stand to view the upper screen (occasional standing is good practice anyway), but not if that would mean getting up and down like a yo-yo.  There may also be merit in moving the chair sideways to view screens at the side, if this is needed with any significant duration. That means the chair and the floor surface would need to lend themselves to free-wheeling (but not too much!).

    With regard to tilt angle, we always recommend that the screen be set facing directly towards the viewer’s face, to minimise the changes in focal length, as you pointed out.  The issue probably would not be significant if the person looks left to right most of the time, but if they are looking up and down a lot, the lens muscles could become fatigued.

    Portrait v. landscape for the screen – the same issues as mentioned above would apply. In spite of the fact that many of us are better at saying ‘yes’ than ‘no’, it is easier to move the head from side-to-side than up and down. In the latter case, we have gravity to contend with, but not so much in the former.  If the screen is placed in portrait mode, there would probably be a fair bit of up and down movement required, which could potentially be tiring. What about the eyes moving up and down compared with sideways?  Do the Chinese (reading top to bottom) tire more quickly than English (reading left to right), or less quickly? There is a comparison worth considering.

    Geoff

    #38989

    GCWesq
    Participant

    A screen over the offending part of the light (attached at ceiling level) can be a solution.

    #38858

    [private user]
    Participant

    Geoff,

    Thanks for the extended reply. I agree that technology is usually ahead of ergonomics but that doesn’t mean we can ignore it. (no, you didn’t suggest that). 

    Large screens certainly represent a challenge not only to our traditional wisdom (assuming it IS wisdom) but to our visual system as well. Yes, we do look easier from side-to-side but I don’t know of any issues that the Chinese have with eyestrain. However, you might consider that the entire Asian population has the highest levels of myopia (nearsightedness) in the world. Hmmmm, just a bit for speculation…..

    I always find it interesting when there is talk of "screen height" because that means so many things to so many people. It DOES depend on where on the screen you’re looking most often but that’s continually changing and unlikely that users can keep viewing that part of the screen continually. The difference with paper is that paper is more mobile and can be more easily relocated in the visual field, whereas the monitor is essentially "locked" in place.

    I still believe that the tilt angle of the monitor should be maintained, regardless of the size of the screen. Looking at the visual posture, the eyes still turn the same way when looking at a near/intermediate distance object. And yes, portrait viewing can be problematic if done for extended periods of time at a close viewing distance.

    Thanks
    Jeff
    Dr. Jeffrey Anshel

    Optometrist

    Corporate Vision Consulting

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