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: During ocular manipulation under general anesthesia , we assessed their eyes by forced duction testing , comparing ocular motility after tumor control with ocular motility at diagnosis .
### Output Text:
During ocular manipulation under general anesthesia , we assessed their eyes by forced duction testing , comparing ocular motility after tumor control with ocular motility at diagnosis . 