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: RESULTS : Ophthalmologists at 15 institutions responded , reporting a total of 3 , 774 indocyanine green angiograms performed on 2 , 820 patients between June 1984 and September 1992 .
### Output Text:
RESULTS : Ophthalmologists at 15 institutions responded , reporting a total of 3 , 774 <span class="chemical">indocyanine green</span> angiograms performed on 2 , 820 patients between June 1984 and September 1992 . 