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Thread: Field of view of the eye

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Field of view of the eye

    Hi!

    I need to discover the approximate FOV for a single eye, gazing straight ahead. Vertical and horizontal, in degrees.

    Thanks in advance for your replies.

    Barry

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    ATO Member OptiBoard Bronze Supporter HarryChiling's Avatar
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    Quote Originally Posted by Barry Santini View Post
    Hi!

    I need to discover the approximate FOV for a single eye, gazing straight ahead. Vertical and horizontal, in degrees.

    Thanks in advance for your replies.

    Barry
    95o Out
    75o Down
    60o In
    60o Up
    about 12-15o temporal and 1.5o below the horizontal is the optic nerve or blind spot which is roughly 7.5o in height and 5.5o in width.

    (these figures use a 3mm white target on a perimeter of 330o if the target was increased the temporal can be pushed to about 110o)

    The Ophthalmic Assistant - Stein, Slatt, Stein pg.395

    Most perimetery is performed on the central 30o and a post yesterday from Darryl confirmed that 30o is used in lens design because apparently beyond this their seems to be head movement along with rotation. Also the first ANSI required off axis powers to be within a set standard for 30o of rotation.

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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    Thnaks, Harry!

    Barry

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    You can deduct a little for big noses or highly inset eyes. Some from top with droopy lids. This like everything else in this racket varies with the patient.
    You might even add a little for big eyed girls.

    Chip

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    What's up? drk's Avatar
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    Love geeky stuff like this...

    Hey, and for an anatomical perspective, notice this:


    Notice that the macula is central, and fifteen visual degrees nasally is the optic n. (physiologic blind spot). Notice that the main retinal "arcades" of the superior and inferior branches of the central retinal artery and veins pretty much circumscribe 30 degrees. That's a working definition of the "posterior pole" of the eye.

    Pathological changes inside the arcades are considered more serious than elsewhere, because it's functionally "the central vision" (although not "dead center" which of course is the foveal 5 degrees or parafoveal 10 degrees).

    The central 30 degrees of vision is approximately the size of a paper plate held at arm's length.

    Notice from Harry's post, the total horizontal field is 150 degrees and vertical field is 130 degrees (average it to 140), so the central part of our vision is thus loosely defined as about 20% and the peripheral vision is loosely defined as about 80%. (Another 80/20 rule in life.)

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    The Man, The Myth, The Legend OptiBoard Gold Supporter Fezz's Avatar
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    Hey Doc,

    Is that some Drusen I see in that picture?

    ;)

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    What's up? drk's Avatar
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    Fezz, you're cruisin' for a drusen?

    Realize also the the entire posterior pole would fit neatly inside a soft contact lens...about 12 mm

    An interesting project would be to extrapolate the size of the central 30 degrees at the spectacle plane...I'm going to guess that it's a circle about 8mm in diameter. Maybe Harry will do this in his head or something.
    Last edited by drk; 03-04-2008 at 04:57 PM. Reason: Scale incorrect

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    Not related but your retinal picture reminded me.

    About 30-35 years ago, I used to take retinal pictures. One of the doctors sent me a patient an I took a picture. Patient had a piece of steel exactly the size of the optic nerver, right over the optic nerve. Steel had been there 20 years. Patient had gone to the doctor's office at time of injury and got mad and left after being kept waiting too long.
    Patient had no symptoms, had no loss of vision (no vision at optic nerve site).
    Doctor remarked that this man was very fortunate the he didn't see an ophthamologist the day of injury or the doctor would have felt compelled to remove the steel fragment and probably done some real damage.

    Chip

    And no, no rust visible in picture. Steel fragment left just as it was.:hammer:

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    ATO Member OptiBoard Bronze Supporter HarryChiling's Avatar
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    Quote Originally Posted by drk
    An interesting project would be to extrapolate the size of the central 30 degrees at the spectacle plane...I'm going to guess that it's a circle about 8mm in diameter. Maybe Harry will do this in his head or something.
    Using Gullstrand:

    n=1.33
    axial length=24.4mm
    anterior cornea=7.7mm

    half the axial length is 12.2mm so you figure

    ray height at corneal plane = tan(30) * 12.2mm
    ray height at corneal plane = 7.04mm

    the cornea is roughly a radius of 7.7mm so:

    tan(refracted angle) = 7.04mm / 7.7mm
    tan(refracted angle) = 0.9148
    refracted angle = 42.45o would be the normal at 7.04mm on the cornea of radius 7.7mm

    42.45o - 30o = 12.45o angle of refraction

    snells law and all:

    1.33 * sin(12.45) = 1 * sin(angle of incidence)
    sin(angle of incidence) = 0.2868
    angle of incidence = 16.7o

    From here that angle and the vertex distance of lets say 13mm:

    ray height at spectacle plane = (tan(16.7) * 13mm) + 7.04mm
    ray height at spectacle plane = 10.9mm radius at the spectacle plane

    That's a diameter of 21.8mm on the spectacle plane which would be the equivalent of a circle slightly smaller than a quarter on the spectacle plane, that's 30o in all directions up, down, left, and right. If I understood that wrong and we are lookign for 15o up, down, left, and right then the answer would be closer to half this figure at 11mm which would be about 2/3rds of a dime.


    That's also assumeing I did the math right, it is 2:30 in the morning and suprise suprise I can't sleep.:(

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    Quote Originally Posted by HarryChiling View Post
    95o Out
    Most perimetery is performed on the central 30o and a post yesterday from Darryl confirmed that 30o is used in lens design because apparently beyond this their seems to be head movement along with rotation. Also the first ANSI required off axis powers to be within a set standard for 30o of rotation.
    Harry, this is IMHO a bit misleading. The +/- 30° for lens design is based on the idea of eye rotation (already), but no head movement. If you consider a fixed eye only (as I assume this thread is all about), you could significantly increase the tolerances for off-axis astigmatism at such large angles without anybody noticing, because the off axis resolution of the fixed is PRETTY poor, only our "built-in" automatic image scanning and composition "firmware" we all have creates the illusion of a large, clear field of view. (That most detailed viewing is only done at the eye optical axis also explains why the lateral color of the eye is insignificant compared to lateral color of the eyeglass, while both have a similar effective nue)

    The visual acuity vs. field angle of a fixed eye is approximately a power law, I remember a nice diagram in a book that I NOW have handy, which says: radius for 0.5 visus (20/40 vision): 2 degrees, 0.1 visus (20/200): 20 degrees, 0.05 visus (20/400): 30 degrees, 0.02 visus (20/1000): 50 degrees. (This is from Warren J. Smith, Modern Optical Engineering, but the original, uncited source is likely a different one)

    Sincerly
    Last edited by xiaowei; 03-07-2008 at 09:51 AM. Reason: Update for acuity vs. field numbers

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    ATO Member OptiBoard Bronze Supporter HarryChiling's Avatar
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    Quote Originally Posted by xiaowei View Post
    Harry, this is IMHO a bit misleading. The +/- 30° for lens design is based on the idea of eye rotation (already), but no head movement.

    I think we may have misunderstood one another, the 30o is like you mentioned without head movement, from what I understood the post iluded to and I have read in a few places I can look them up at some point that beyond 30o we start to move our heads. For example if we were to try and view an object 95o in our periphery the head would more than likely rotate lest just say for example 65o and the eyes would rotate 30o of course if we were to try and focus on that object we would continue to rotate the head untill our gaze was directly upon the object with next to no rotation of the eye. I think I understand what your saying that the fovea is a small area where 20/20 or better vision occurs and as we get farther from here, larger agles; the density of cones is lacking so the visual acuity drops as well.

    Man xiaowei, your seem to be on point with your responses. Was your PHD in optics or another area of physics?

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    What's up? drk's Avatar
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    Yes, the mysterious Xiaowei is very good...

    Thanks for the good math, Harry.

    So, the central 30 degrees of vision (that we are trying to conceptualize) will be "serviced" by a circular section of the spectacle lens that is about 11mm in diameter from the MRP (when looking straight ahead, say, driving down the road staring at the horizon). That's less than a dime.

    So, let's use the radius of 5 mm, to keep it simple. That means if a seg line, or a progressive corridor encroached on this "personal space" it would be probably rather distracting. Anyone fit segs that close to the pupil? Maybe in a TF...What about where the progression begins in a lens? Zeiss is said to have begun the progression 4 mm below the fitting cross...everyone else is 2 mm, right? I know I fudge it downwards by 1mm routinely...

    What about scratches on a lens? If inside the "central dime", they would visually bother people the most, I'd say.

    Another application of the very good "dime" construct: how does a dime compare to a cut out and mounted bifocal segment? Is the seg only a paltry 9 mm tall? That will not be perceived as a "full field of view". You'd need about half of a Round 22, or somewhat less than half (40%) of the D28.

    What about a 7 mm tall intermediate seg? Doesn't meet the dime criterion...you'd need those 14x35's if you want to spend any serious time on the computer.

    What about the rough area of the near zone of a short-corridor progressive? Is it roughly 3.1416 x 5 mm = 16 mm2 in area? (Who knows on that one...?).



    One final application of the "dime"...how can IZON optimize a lens with numerous dime-sized packets of optics? Can't believe that one, easily...

  13. #13
    ATO Member OptiBoard Bronze Supporter HarryChiling's Avatar
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    Quote Originally Posted by drk View Post
    Yes, the mysterious Xiaowei is very good...

    Thanks for the good math, Harry.

    So, the central 30 degrees of vision (that we are trying to conceptualize) will be "serviced" by a circular section of the spectacle lens that is about 11mm in diameter from the MRP (when looking straight ahead, say, driving down the road staring at the horizon). That's less than a dime.

    So, let's use the radius of 5 mm, to keep it simple. That means if a seg line, or a progressive corridor encroached on this "personal space" it would be probably rather distracting. Anyone fit segs that close to the pupil? Maybe in a TF...What about where the progression begins in a lens? Zeiss is said to have begun the progression 4 mm below the fitting cross...everyone else is 2 mm, right? I know I fudge it downwards by 1mm routinely...

    What about scratches on a lens? If inside the "central dime", they would visually bother people the most, I'd say.

    Another application of the very good "dime" construct: how does a dime compare to a cut out and mounted bifocal segment? Is the seg only a paltry 9 mm tall? That will not be perceived as a "full field of view". You'd need about half of a Round 22, or somewhat less than half (40%) of the D28.

    What about a 7 mm tall intermediate seg? Doesn't meet the dime criterion...you'd need those 14x35's if you want to spend any serious time on the computer.

    What about the rough area of the near zone of a short-corridor progressive? Is it roughly 3.1416 x 5 mm = 16 mm2 in area? (Who knows on that one...?).



    One final application of the "dime"...how can IZON optimize a lens with numerous dime-sized packets of optics? Can't believe that one, easily...
    30 degree's both ways is more a quarter and I think that's what were using, but I get your point.

    As for the IZON, unless the lenses were always stationary (ie they moved with the eye) they can only really be optimized for one positions of gaze I would assume straight ahead, thats nto saying that this would be the only spot but any viewing off axis would enevitably be a comprimise as they would have to blend that optimization I would think.

    As for the scratch my favorite pair of glasses got hit with a screw right in the center a week after I go them, I have been wearing them for 4 years now and that scratch is still there, I don't have the ability to focus close enough for it to be a problem to me.

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