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 all subjects with history of EMB - induced optic neuropathy , there was a mean loss of 72 % nerve fiber layer thickness in the temporal quadrant ( patient A , with eventual recovery of visual acuity and fields , 58 % loss ; patient B , with intermediate visual deficits , 68 % loss ; patient C , with chronic visual deficits , 90 % loss ) , with an average mean optic nerve thickness of 26 + / - 16 microm .
### Output Text:
In all subjects with history of <span class="chemical">EMB</span> - induced optic neuropathy , there was a mean loss of 72 % nerve fiber layer thickness in the temporal quadrant ( patient A , with eventual recovery of visual acuity and fields , 58 % loss ; patient B , with intermediate visual deficits , 68 % loss ; patient C , with chronic visual deficits , 90 % loss ) , with an average mean optic nerve thickness of 26 + / - 16 microm . 