PAROS

PAROS (PARaxial Optical fundus Scaling) calculates the true magnification of fundus photographs from the optical characteristics of the patient’s eye and fundus camera, correcting for the scaling errors that otherwise complicate quantitative measurements on fundus images. The method, its validation and a first implementation are described in Pors et al. (2024). A basic version of PAROS can be tried online without installing anything.

The package provides two main building blocks: a calibration notebook that derives camera-specific constants from phantom-eye measurements, and a magnification notebook that combines these constants with a patient’s biometry to calculate the true scaling of their fundus photographs. Camera calibration constants contributed by other centres can be added to a shared lookup table, so PAROS can gradually be extended to more fundus camera models. Because the current implementation was calibrated for the camera and software used at the MReye group’s center, we recommend repeating the calibration step for other setups before using PAROS for your quantitative measurements.

• Patient‐specific mapping of fundus photographs to three‐dimensional ocular imaging

  Haasjes, Vu and Beenakker
  Medical Physics (2025), doi: 10.1002/mp.17576 
• Correction Method for Optical Scaling of Fundoscopy Images: Development, Validation, and First Implementation

  Pors, Haasjes, Vught, Hoes, Luyten, Rijn, Vu, Rasch, Horeweg and Beenakker
  Investigative Opthalmology & Visual Science (2024), doi: 10.1167/iovs.65.1.43 
• Longitudinal studies assessing retinal vascular characteristics in childhood and adolescence must account for ocular growth

  Rauscher and Heitmar
  Atherosclerosis (2024), doi: 10.1016/j.atherosclerosis.2024.117611

License

MIT

Last updated

Jul 1, 2026

Requires Python

>=3.10

Dependencies

• matplotlib
• numpy
• pandas
• scipy
• sympy
• typing-extensions >=4.12.2 (only if python_full_version < '3.11')