In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: RESULTS : Mean right eye MRD at presentation was 36 . 98 degrees ( range 22 . 25 - 51 . 0 ) , compared to 38 . 40 degrees ( range 22 . 5 - 49 . 75 ) after follow - up ; P = 0 . 338 unpaired t - test .
### Output Text:
RESULTS : Mean right eye MRD at presentation was 36 . 98 degrees ( range 22 . 25 - 51 . 0 ) , compared to 38 . 40 degrees ( range 22 . 5 - 49 . 75 ) after follow - up ; P = 0 . 338 unpaired t - test . 