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: Screening , including Humphrey 10 - 2 visual field assessment , is recommended 2 years after the initial baseline and yearly thereafter .
### Output Text:
Screening , including Humphrey 10 - 2 visual field assessment , is recommended 2 years after the initial baseline and yearly thereafter . 