Matrix to Table - Index/Match return multiple column header(s) [multiple occurrences]

I dont think this is possible using a formula as you have merged columns.
You may be able to use a formula if you have the same number of columns per heading, ie
11 columns for Areas
11 columns for Head
11 columns for Eye
etc

However, this could cause complications
First, you would have blank unused columns

Secondly, to extract the heading name you would need to place the name linearly in each header group, e.g.
Areas has 11 columns and "Areas" is in the first column of that group.
"Head" is in the first column of the Head group.
"Eye is in the first column of the Eye group
etc
You could then use one formula to extract the heading names as you know the heading name is an equal amount of columns away, e.g. column 1, column 12, column 23 (every 11 columns)

Thirdly, if you add or delete a column for a header group you would have to reflect that column addition/deletion in the other columns or the formula that extracts headings would be out, ie delete a column from Areas so it now contains 10 columns then you would have to delete a column from the other headers of Head, Eye etc so they contain 10 columns.

Based on this, you would be better of using VBA.