In terms of ophthalmic measure, central visual acuity of 20/200 or less in the better eye with correcting glasses is generally considered as economic blindness. A field defect in which the peripheral field has contracted to such an extent that the widest diameter of visual field subtends at an angular distance of no greater than 20 degrees is considered equally disabling.

Permanent and total diability is defined to mean a physical or mental condition sufficiently severe to prevent the individual from engaging in useful occupations within his competence, such as holding a job or homemaking, and of such a nature that no substantial improvement can be expected within the foreseeable future, or it will probably remain static or progress. This definition is not intended to except individuals who are capable of self-care or who may be subject to rehabilitation or to physical restoration. Neither the word “permanent” nor the word “total” is used in the absolute sense.