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: They both reported short episodes of transient visual disturbances , which appeared immediately after starting treatment with risperidone .
### Output Text:
They both reported short episodes of transient visual disturbances , which appeared immediately after starting treatment with <span class="chemical">risperidone</span> . 