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: All patients underwent objective assessment of electrophysiological function ( wide - field multifocal electroretinography ) and conventional visual field testing ( static perimetry ) .
### Output Text:
All patients underwent objective assessment of electrophysiological function ( wide - field multifocal electroretinography ) and conventional visual field testing ( static perimetry ) . 