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

# cylinder

Part of the correction for astigmatism that measures the strength of the correction.

## Declaration

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

## Discussion

Discussion This quantity measures the strength of the correction in diopter() units. The range is -3.0 to 3.0.

## See Also

### Accessing lens specification data

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