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 both sets ( four ) of eyes of the subjects with persistent visual deficits ( patients B and C ) , there was an average loss of 79 % of nerve fiber thickness in the temporal quadrant .
### Output Text:
In both sets ( four ) of eyes of the subjects with persistent visual deficits ( patients B and C ) , there was an average loss of 79 % of nerve fiber thickness in the temporal quadrant . 