Radius size of the peripapillary scan circle of Cirrus HD-OCT as calculated according to the Littmann formula in eyes with different axial lengths
| Axial length (mm) | Scan circle radius (mm) |
| 20 | 1.39 |
| 21 | 1.47 |
| 22 | 1.54 |
| 23 | 1.62 |
| 24 | 1.69 |
| 24.46 | 1.73 |
| 25 | 1.77 |
| 26 | 1.85 |
| 27 | 1.92 |
| 28 | 2.00 |
| 29 | 2.08 |
| 30 | 2.15 |
When the axial length is 24.46 mm, there is no magnification.