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 ocular myasthenia associated with combination therapy of pegylated IFN alpha - 2b and ribavirin for CHC is very rarely reported ; therefore , we present this case with a review of the various eye complications of IFN therapy .
### Output Text:
The ocular myasthenia associated with combination therapy of <span class="chemical">pegylated IFN alpha - 2b</span> and <span class="chemical">ribavirin</span> for CHC is very rarely reported ; therefore , we present this case with a review of the various eye complications of <span class="chemical">IFN</span> therapy . 