You can see modification history of "description" field for any file. To view history, press "History" button:
For "Сomments" this button also available in the upper right corner:
You will see "Modification history" dialog. Here you can observe the history of updates, view any version and compare versions.
Select version from the list to see description in the window below. Use Ctrl+click to select two versions you want to compare. In the window below you can see both versions with highlighted differences. Added, modified and removed lines shown in different colours:
By default, files shown in "Wiki-notation" mode to see changes. However you can change to "Preview" when single version selected.