---
title: axis
framework: healthkit
role: symbol
role_heading: Instance Property
path: healthkit/hklensspecification/axis
---

# axis

Part of the correction for astigmatism that measures the orientation fo the correction.

## Declaration

```swift
@NSCopying var axis: HKQuantity? { get }
```

## Discussion

Discussion This quantity measures the orientation of the correction in degreeAngle() units.

## See Also

### Accessing lens specification data

- [sphere](healthkit/hklensspecification/sphere.md)
- [cylinder](healthkit/hklensspecification/cylinder.md)
- [addPower](healthkit/hklensspecification/addpower.md)