Quick Question ! How the Gaze of our eyes is decided? Can we visually measure distance accurately?

I asked myself a question today, How far can our eyes watch the distsnt object, I answered, may be up to the Horizon, but then I had anothet question, we can see Sun, Moon, Stars very far away. Is it true that we can see endless distance, or depends on the source of light. I may be asking silly but I wish to post. Thanks. Kiran Trivedi ( Kiran means Ray of Light!!)

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4 thoughts on “Quick Question ! How the Gaze of our eyes is decided? Can we visually measure distance accurately?

  1. Anything that can be imaged onto the retina by a lens can be ‘seen’, so I believe the answer to this would be a ‘Yes’! After all, a convex lens can focus even a source present an infinite distance from the lens.

    What would be difficult, however, is the resolution of the image, since you don’t ‘see’ something unless you ‘perceive’ the image. The focusing does happen, but I am guessing that there is a upper limit on the resolution of the eye (the theoretical limit would, of course, be dependent on the receptor dimension, the lens-to-retina distance, and also the distance of the object). Thus, for an object of a finite size, the distance of an object that can be seen is limited.

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  2. Continuing from my previous reply, if the lens may be approximated to a thin lens, the theoretical maximum distance of visibility of an object of size O, if each receptor is of dimension R and the width of the eyeball is E, is O * E/R

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  3. For a point of light such as a candle flame, we can see it up to about 45km (30 miles) away. For something to appear spatially extended (not just a point), it needs to stimulate at least two adjacent cone cells in the retina. For this an object must subtend an angle of at least 1 minute of arc at the eye. This is where we get the letter chart and 20/20 (6/6) visual acuity. When you divide the lower number by the upper number you get the angle it subtends e.g 20/40 is 2 minutes of arc and 20/20 is 1 minute of arc. While some individuals can resolve detail that is a little smaller than 20/20, it is a good metric when testing visual acuity and can be used at all distances (the letter or object just need to be bigger or smaller depending on your distance from it). Hope this helps.
    Cathy

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    • Dear Dr. Cathey, again Thanks a lot, your answers are fully informative and generates more interest, so in general what should be the size of the light source in general, at last on earth and routine life, we normally stop at horizon as we cant see beyond the Earth curvature.just a quick questions, my questions may be useless or silly but I am learning from your answers

      Thanks

      Kiran Trivedi

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