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: The contralateral control eyes , which did not receive dexamethasone , maintained a stable intraocular pressure during the same period .
### Output Text:
The contralateral control eyes , which did not receive <span class="chemical">dexamethasone</span> , maintained a stable intraocular pressure during the same period . 