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: METHODS : Three subjects with a history of ethambutol ( EMB ) - induced optic neuropathy of short - , intermediate - , and long - term visual deficits were administered a full neuro - ophthalmologic examination including visual acuity , color vision , contrast sensitivity , and fundus examination .
### Output Text:
METHODS : Three subjects with a history of <span class="chemical">ethambutol</span> ( <span class="chemical">EMB</span> ) - induced optic neuropathy of short - , intermediate - , and long - term visual deficits were administered a full neuro - ophthalmologic examination including visual acuity , color vision , contrast sensitivity , and fundus examination . 