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: Similar to patients , withdrawal of dexamethasone treatment reduced elevated IOP and ER stress in this animal model .
### Output Text:
Similar to patients , withdrawal of <span class="chemical">dexamethasone</span> treatment reduced elevated IOP and ER stress in this animal model . 