The Cup-to-Disc Ratio (CDR) measures the ratio between the areas of the cup and the disc of the optic nerve, aiding in the identification of glaucoma-related alterations. To utilize this feature:

1. Select the desired image for analysis from the gallery
2. Next, click on the editing icon located at the top right corner of the screen
3. Select the CDR option on the bottom menu
4. Move the circles to encompass the areas of interest and use the locks to keep their position while the other is altered
Green circle should be moved to Disk.
Purple circle should be moved to Cup.
5. Click in the “Check icon” to save the edit.

Usually, healthy eyes follow the rule Inferior ≥ Superior ≥ Nasal ≥ Temporal.