Because they were often worn by people involved in accounting, auditing, economics, and budgeting, they became associated with these activities.
Green eyeshades or dealer's visors are a type of visor that were worn most often from the late 19th century to the mid-20th century by accountants, telegraphers, copy editors, and others engaged in vision-intensive, detail-oriented occupations to lessen eye strain due to early incandescent lights and candles, which tended to be harsh (the classic banker's lamp had a green shade for similar reasons).
