Special Rules For People Who Are Blind   Social Security defines blindness as central visual acuity up of 20/200 or less in the better eye with best correction, or a limitation in the field of vision in the better eye so that the widest diameter of the visual field subtends an angle of 20 degrees or less (tunnel vision). Under SSDI this condition has to have lasted or is expected to last at least 12 months.  There is no duration requirement for blindness under SSI. For the year 2008 substantial gainful activity for a person who is blind is $1570 per month.   Social Security decides substantial gainful activity for people who are self-employed based solely on earnings. After your 55th birthday if you're earnings are at substantial gainful activity but your work requires a lower level of skill or ability than the work that you did before age 55 benefits are only suspended not terminated. SGA is not applied under SSI to people who are blind.  SGA is not a factor for SSI eligibility Blind Work Expenses Under SSI Social Security does not count any earned income used as expenses needed to earn that income in deciding SSI eligibility or payment amount.  In order to qualify you must be under age 65 for a 65 or older and received SSI payments due to blindness.  Some examples of blind work expenses are: guide dog expenses, transportation to and from work, federal state and local income taxes, Social Security taxes, attendant care expenses, visual and sensory aids, translation of materials into Braille, professional association fees, or union dues.