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: BACKGROUND : Although intravitreal aminoglycosides have substantially improved visual prognosis in endophthalmitis , macular infarction may impair full visual recovery .
### Output Text:
BACKGROUND : Although intravitreal <span class="chemical">aminoglycosides</span> have substantially improved visual prognosis in endophthalmitis , macular infarction may impair full visual recovery . 