John K. Johnstone

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In general, two quadric surface intersect in a space quartic curve. However, the intersection frequently degenerates to a collection of plane curves. Degenerate cases are frequent in geometric/solid modeling because degeneracies are often required by design. Their detection is important because degenerate intersections can be computed more easily and allow(More)
PURPOSE This study explores variation in the axial location of Bruch's membrane opening (BMO) to determine if this reference plane varies with age and race. METHODS There were 168 spectral-domain optical coherence tomography (SDOCT) optic nerve head volumes that were obtained from healthy subjects and manually delineated within 24 axial slices to develop(More)
We present a method for constructing tensor product Bezier surfaces from contour (cross-section) data. Minimal area triangulations are used to guide the surface construction , and the final surface reflects the optimality of the triangulation. The resulting surface differs from the initial triangulation in two important ways: it is smooth (as opposed to the(More)
PURPOSE To determine if laminar depth (LD) and prelaminar tissue volume (PTV) are associated with age and race in healthy human eyes. METHODS Optic nerve head images from enhanced depth imaging spectral-domain optical coherence tomography of 166 normal eyes from 84 subjects of African descent (AD) and European descent (ED) were manually delineated to(More)
PURPOSE This study examined the association between peripapillary choroidal thickness (PCT) with age and race in a group of African descent (AD) and European descent (ED) subjects with normal eyes. METHODS Optic nerve head images from enhanced depth imaging spectral-domain optical coherence tomography of 166 normal eyes from 84 subjects of AD and ED were(More)
In general, two quadric surfaces intersect in a space quartic curve. However, the intersection curve frequently degenerates to a collection of plane curves. These degenerate cases introduce problems into the general intersection algorithms and are difficult to implement in a reliable way. In this paper, we investigate this problem for natural quadrics.(More)