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- Herven Abelman
- Ophthalmic & physiological optics : the journalâ€¦
- 2006

General or local variations of the refractive elements in the eye, called irregular astigmatism, may manifest as non-orthogonal meridians when each principal meridian on the front surface of a corneaâ€¦ (More)

- Herven Abelman, Shirley Abelman
- Comp. Math. Methods in Medicine
- 2014

Lensometers and keratometers yield powers along perpendicular meridians even if the principal meridians of the lens and the cornea are oblique. From each such instrument, multiple raw dataâ€¦ (More)

- Herven Abelman, Shirley Abelman
- Journal of biomedical optics
- 2009

We seek to analyze the geometry and explain how bounds and intervals of nonzero purely cylindrical powers are obtained and applied in symmetric dioptric power space and envisaged in the clinic. Theâ€¦ (More)

- Shirley Abelman, Herven Abelman
- Computers & Mathematics with Applications
- 2008

Monochromatic light rays incident from some directions on a glass prism emerge from the prism with their direction changed. For many thick prisms, emerging light rays are obscured at a boundary. Theâ€¦ (More)

- Herven Abelman, S Abelman
- Ophthalmic & physiological optics : the journalâ€¦
- 2007

During the refraction procedure, the power of the nearest equivalent sphere lens, known as the scalar power, is conserved within upper and lower bounds in the sphere (and cylinder) lens powers.â€¦ (More)

- Herven Abelman, Shirley Abelman
- Comp. Math. Methods in Medicine
- 2014

Unacceptable principal powers in well-centred lenses may require a toric over-refraction which differs in nature from the one where correct powers have misplaced meridians. This paper calculatesâ€¦ (More)

- Herven Abelman, S Abelman
- Ophthalmic & physiological optics : the journalâ€¦
- 2007

Principal meridional powers of thick astigmatic systems, like the eye, are not necessarily at right angles. The consequence is a class of phenomena included in the category commonly described asâ€¦ (More)

- Herven Abelman, Shirley Abelman
- Optometry and vision science : officialâ€¦
- 2007

PURPOSE
The purpose of this article is to investigate the invariance and isomorphism of error cells with cylinder power measured positively and negatively in the cylinder-sphere plane. Cells withâ€¦ (More)

- W. F. Harris, Herven Abelman
- Ophthalmic & physiological optics : the journalâ€¦
- 1991

A single approximate matrix expression is derived that gives the thickness at any point on any lens. The lens may have dioptric power or prism power or both. The expression gives, amongst otherâ€¦ (More)

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