Investigating the Level of Observing the Evaluation Criteria for User Interface in library services providing to the blind and deaf users in the word

Purpose: Digital library user interfaces has a determining role in desirable performance of this kind of libraries. Digital Library service providers to the blind and deaf users will have their best performance when the users (deaf and blind users) could have a proper interaction with them. This study aims to evaluate and analyze the criteria related to user interface in digital libraries service provider to the blind and deaf users in the world.  Methodology: This is an applied and evaluative study. This study has been used library research method for extracting criteria and descriptive survey method for everything from evaluating library. A checklist consist of 13 criteria (Screen capabilities, Ability of organizing the screen, Search facilities, Links, Visual symbols and images, Options for customizing the texts, Help services and Tips, Error message alert, Interaction and feedback facilities, user interface Language, User controls, Library resources in various format, Study facilities of retrieved resources from the library) and 109 component is prepared. Then have been finalized by using the Delphi method and completed for each Library. 12 digital library service providers to blind and deaf user in the world perform the population. Finding: Results of the study showed that the criteria of '' user interface language '' (with 97.92 %) and the criteria of '' user control'' (with 9.67 %) reached the highest and lowest scores respectively. Among the 12 digital libraries investigated worldwide, "Digital library for the blind" with respect 63.53 reached the maximum and "U.S. National Library Service for Blind" with respect 37.62 grasped the minimum levels.