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: In addition , OCT ( OCT 3000 , Humphrey - Zeiss , Dublin , CA ) was performed on both eyes of each subject using the retinal nerve fiber layer ( RNFL ) analysis protocol .
### Output Text:
In addition , OCT ( OCT 3000 , Humphrey - Zeiss , Dublin , CA ) was performed on both eyes of each subject using the retinal nerve fiber layer ( RNFL ) analysis protocol . 