This depends on whether your vision loss is directly work-related. If it is, your employer may be liable to assist you with related financial, medical, and vocational issues. If there is no direct work-related cause, your employer is not as clearly obligated. However, in either case, the primary issue is this: If you want to keep your job, it will depend on whether you're still able to do the "essential functions" for which you are responsible.
Discuss your concerns with a Vocational Rehabilitation Counselor from your state agency [1] for the disabled, blind or visually impaired, and learn as much as you can about The Americans with Disabilities Act [2] (ADA):
The U.S. Equal Employment Opportunity Commission [5] (EEOC) enforces the employment provisions of the ADA. The EEOC website provides a series of Questions and Answers About Blindness and Vision Impairments in the Workplace and the Americans with Disabilities Act [6] that address the following issues:
ADA states that employers cannot prevent an individual from maintaining his or her job if the individual can perform the "essential functions" of that job. The employer is required to provide "reasonable accommodations" that allow the employee to perform his or her job effectively.
In some instances, the employer may contend that the provision of work place adjustments would be too costly, or provide "undue hardship" for his/her business or organization; in most situations, however, the employee can resolve these issues by learning about appropriate resources that will provide information and, in some cases, financial assistance. You can learn more about your rights by requesting a copy of the ADA Law (Public Law 101-336-July 26 1990--104 STAT. 327-378) from the U.S. Equal Employment Opportunity Commission.
Links:
[1] http://www.visionaware.org/find_vision_rehabilitation_vision_services_in_your_state
[2] http://www.jan.wvu.edu/links/adalinks.htm
[3] http://www.eeoc.gov/policy/ada.html
[4] http://www.eeoc.gov/policy/rehab.html
[5] http://eeoc.gov/
[6] http://www.eeoc.gov/facts/blindness.html
[7] http://www.eeoc.gov/facts/accommodation.html