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: He complained of pain and visual disturbance in the ipsilateral eye 30 h after the injection .
### Output Text:
He complained of pain and visual disturbance in the ipsilateral eye 30 h after the injection . 