SSA has two categories of eligibility criteria for SSDI and the individual must meet both categories to qualify. SSA will first determine if an individual meets the nonmedical eligibility criteria. SSDI is an entitlement program. A person qualifies for this program based on nonmedical eligibility criteria when they accumulate enough work credits by paying into the Federal Income Contributions Act (FICA taxes). This is why it is called an entitlement program because you paid into disability insurance. Once a person meets the nonmedical eligibility criteria, SSA will review the application to determine if an individual meets their definition of medical eligibility. The medical evidence has to show that the person is unable to work and earn $1090.00 per month or $1820.00 per month for individuals who are blind in 2015. For more detailed information on this program click this link (can provide the link to SSA Website explaining SSDI).