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: The underlying pathology of glucocorticoid - induced glaucoma is not fully understood , due in part to lack of an appropriate animal model .
### Output Text:
The underlying pathology of glucocorticoid - induced glaucoma is not fully understood , due in part to lack of an appropriate animal model . 