Page 154 - Nov- Dec 2024

CYLINDRICAL

LENSES

& CYLINDRICAL

CORRECTION

ertain magnifying glasses,
designed specifically for reading wide
Ccolumns of print, are examples of
cylindrical lenses. For a simple cylindrical
lens, the surfaces of the lens represent
portions of a cylinder’s surface. Consider
how such a lens refracts light: when
a cylindrical lens acts as a magnifier, it
magnifies only in one direction. For instance,
the magnifier shown enlarges letters in height
but not in width.

Similarly, when a cylindrical lens puts an
optical system out of focus and introduces usually start by determining the best spherical
blur, the blur occurs only in one direction. This correction. If astigmatism is present, the next
specific type of blur results from uncorrected step involves compensating for it by adding the
astigmatism. The letters appear smeared correct amount of cylindrical correction.
directionally, resembling an artist smudging
charcoal with their thumb. A cylindrical lens UNDERSTANDING ASTIGMATISM AND
of the appropriate power can correct this THE ROLE OF AXIS
kind of blur. When viewing an eye chart, this
directional blur manifests, as described. One Astigmatism causes a directional blur, where
can compare this to the kind of blur that is the letters appear smeared in a specific direction,
evenly distributed in all directions. as though smudged with a thumb on charcoal. In
contrast, a spherical lens behaves uniformly in all
When an eye doctor measures the eye directions, maintaining consistent magnification
during a procedure known as refraction, they or blurring regardless of orientation.

148 | THE INDIAN OPTICIAN | NOV-DEC 2024 OPTOMETRY