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: Tests of basic visual function included high - and low - contrast visual acuity ( HCVA and LCVA ) , Pelli - Robson contrast threshold ( CT ) and Goldmann perimetry ( FIELDS ) .
### Output Text:
Tests of basic visual function included high - and low - contrast visual acuity ( HCVA and LCVA ) , Pelli - Robson contrast threshold ( CT ) and Goldmann perimetry ( FIELDS ) . 