Difference between revisions of Axis

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'''Axis''' is the orientation of the [[cylinder]] portion of your lens, used to compensate for [[astigmatism]]. You don't have an axis value if you don't have [[astigmatism]]. From the lens wearer's perspective, 0 degrees of axis is horizontal, and increasing values move clockwise around the eye.  The axis of cylinder is symmetrical, so it only goes from 0 to 180 degrees.
'''Axis''' is the orientation of the [[cylinder]] portion of your lens, used to compensate for [[astigmatism]]. You don't have an axis value if you don't have [[astigmatism]]. From the lens wearer's perspective, 0 degrees of axis is horizontal, and increasing values move clockwise around the eye.  The axis of cylinder is symmetrical, so it only goes from 0 to 180 degrees.
An axis near 90 degrees is sometimes called "with the rule" and near 180 degrees "against the rule".  "With the rule" is more common in young children, while "against the rule" is more common after starting school.<ref>{{Cite journal |last=Dobson |first=V. |last2=Fulton |first2=A. B. |last3=Sebris |first3=S. L. |date=1984-01-01 |title=Cycloplegic refractions of infants and young children: the axis of astigmatism. |url=https://iovs.arvojournals.org/article.aspx?articleid=2159731 |journal=Investigative Ophthalmology & Visual Science |language=en |volume=25 |issue=1 |pages=83–87 |issn=1552-5783}}</ref>


The axis of astigmatism can be measured with a [[stenopaeic slit]] or [[JCC lens]] but the use of these tools is complex and easily misunderstood, it's usually best to get your axis from your most recent [[prescription]].
The axis of astigmatism can be measured with a [[stenopaeic slit]] or [[JCC lens]] but the use of these tools is complex and easily misunderstood, it's usually best to get your axis from your most recent [[prescription]].

Revision as of 16:33, 25 June 2020

Axis is the orientation of the cylinder portion of your lens, used to compensate for astigmatism. You don't have an axis value if you don't have astigmatism. From the lens wearer's perspective, 0 degrees of axis is horizontal, and increasing values move clockwise around the eye. The axis of cylinder is symmetrical, so it only goes from 0 to 180 degrees.

An axis near 90 degrees is sometimes called "with the rule" and near 180 degrees "against the rule". "With the rule" is more common in young children, while "against the rule" is more common after starting school.[1]

The axis of astigmatism can be measured with a stenopaeic slit or JCC lens but the use of these tools is complex and easily misunderstood, it's usually best to get your axis from your most recent prescription.

References

  1. Dobson, V.; Fulton, A. B.; Sebris, S. L. (1984-01-01). "Cycloplegic refractions of infants and young children: the axis of astigmatism". Investigative Ophthalmology & Visual Science. 25 (1): 83–87. ISSN 1552-5783.Page Module:Citation/CS1/styles.css has no content.