The term "180 axis" typically refers to the prescription for corrective lenses, particularly when discussing astigmatism. In eyeglass prescriptions, the "axis" indicates the orientation of the astigmatism correction needed in the lens.
Here’s a breakdown of what "180 axis" means in detail:
Astigmatism: Astigmatism is a common refractive error caused by an irregular shape of the cornea or lens in the eye. Instead of being perfectly round, the cornea is shaped more like a football, which leads to decreased sharpness of vision.
Axis: In the context of astigmatism, the axis is measured in degrees and indicates the orientation of the cylindrical power that is needed to correct the astigmatism. It ranges from 1 to 180 degrees.
Interpretation of "180 Axis":
- If an eye prescription indicates a "180 axis," it means that the cylindrical power correction is oriented horizontally (or at 180 degrees) across the lens.
- This tells the optician where to apply the astigmatism correction and is crucial for ensuring that patients receive the appropriate vision correction.
Eye Prescription Example: An eye prescription may include several components:
- Sphere (SPH): Indicates how nearsighted or farsighted a person is.
- Cylinder (CYL): Refers to the amount of astigmatism correction.
- Axis: Specifies the orientation of the astigmatism correction.
For example, a prescription might read:
- Right Eye (OD): -2.00 SPH, -1.00 CYL, 180 AXIS
- Left Eye (OS): -2.00 SPH, -1.00 CYL, 90 AXIS
Visual Impact: For someone with an axis of 180, the corrective lenses will help focus light appropriately on the retina, thus improving vision that may otherwise appear distorted or blurred due to the irregular corneal shape.
- Importance of Accurate Measurement: It’s crucial that the axis measurement is accurate because even a small deviation can result in blurred vision or discomfort when wearing glasses.
In summary, a "180 axis" in an eye prescription is a specification used to correct astigmatism by indicating the orientation needed for the cylindrical power in the lenses.