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Axial Magnification from Distance and Near Corrections

Axial Magnification from Distance and Near Corrections

Axial Magnification from Distance and Near Corrections

Gregg Baldwin OD
Gregg Baldwin OD

FREE
FREE
FREE

FREE
FREE
FREE

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FREE
FREE
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FREE
FREE
Normal Price: FREE FREE

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Launch date: 11 Nov 2018
Expiry Date:

Last updated: 27 Nov 2018

Reference: 192927

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Course Availability

This course is only available to trainees days after purchase. It would need to be repurchased by the trainee if not completed in the allotted time period. This course is no longer available. You will need to repurchase if you wish to take the course again.

Description

Equal arcs along a circle subtend equal angles along that circle. Therefore, certain triangles within a circle can be shown to have the same shape, with their sides forming ratio equalities. Cyclic quadrilaterals can then describe equalities with multiple ratios, and these multivariable relationships can be used to find triangles with other triangles. This plane geometry approach was used by Isaac Barrow in 1667 to describe tangential refraction along a line and at a circle, without trigonometry, algebra, or calculus. It is particularly suited for clinicians in the field of low vision and ophthalmic optics, since it requires no math background beyond high school plane geometry, and encourages a spatial understanding devoid of sign convention and jargon. For those clinicians wishing to have more than a working knowledge of the subject of

axial magnification, I have drawn a progression of geometric figures to cover the necessary preliminary concepts, each building on the previous, with labeled points maintaining their significance until noted otherwise. Axial magnification is presented only after a thorough spatial representation of tangential refraction along a line and a circle. In order to visualize the relevant axial ratio equalities involved using triangles, the optic axis is then represented as a circle of infinite radius, and the sign convention remains unnecessary.

Objectives

With minimal English, describe the necessary geometrical optics for a presentation on axial magnification using a progression of figures.
Each figure contains labeled points that maintain their significance until noted otherwise, so that the seventy-four figures essentially comprise one very complex figure, in order to give a sense of continuity throughout. Labels such as "The Law of Cosines" are intentionally omitted so the relevant relationships are studied in progression, rather than presumed. Some geometrical figures are included that only function to further illustrate concepts already proven, and these are intentionally not labeled as such, in order to require the material to be absorbed slowly, with a sense of fullness, context, and symmetry. A test was omitted because the scope of this course is essentially a curriculum.
Gregg Baldwin OD

Author Information Play Video Bio

Gregg Baldwin OD

Gregg Baldwin, OD, optometrist and low vision examiner, the Virginia Department for the Blind and Vision Impaired, 397 Azalea Ave., Richmond, VA 23227; email: gbaldwinod@gmail.com.

1983 graduate of The Ohio State University College of Optometry; previously US Public Health Service commissioned corps; Indian Health Services, Alaska and Arizona.

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