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Thread: Pursuing Optometry

  1. #1 Pursuing Optometry 
    New Member
    Join Date
    Mar 2014
    A final year optometry student asked me '' What is a spherical eye'' when i responded ''An eye where the cornea is a perfect sphere or a sphere'' he asked me to explain in simple terms.. i dont know what else to say, also he asked what is the power or give examples of powers of spherical eyes.

    I'm baffled by this because i know of spherical corrective lenses for myopia and hyperopia but nothing about spherical eye and the power.
    Help please

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  3. #2  
    Forum Cosmic Wizard
    Join Date
    Dec 2013
    A normal cornea should be about 60 diopters. If it is much more or less it will likely require correction.
    The diopter is the reciprocal of the focal length in meters so 60 diopters gives 16.67mm from the cornea to the retina.

    I have no idea how I know that, but if you want to work out the focal length to the retina when the eye is focused at infinity 60 diopters will be about right.

    Edit: It is more about dealing with an astigmatic lens.
    The reason you call a lens spherical is because it would be like taking a slice of the side of a sphere instead of from an ovoid shape. A spherical lens or mirror has the same focal length in each direction across it. Getting a spherical grind on a lens blank can be a real struggle if you forget to change directions often enough in the grinding.

    Last edited by dan hunter; March 5th, 2014 at 02:23 PM.
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  4. #3  
    Join Date
    Apr 2007
    Literally, a spherical eye would be an eye that is a perfect sphere, but I don't think that exists. It is probably optometrist jargon for an eye that only requires spherical correction, i.e., has no astigmatism. If there is astigmatism, then it also requires cylindrical correction. But this is only a guess on my part.
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