Definitions of deafblindness and congenital deafblindness.

In order to compile knowledge on deafblindness (DB) and congenital deafblindness (CDB), one important factor is comparison of results between different scientific studies. In an attempt to do a systematic review of the literature on cognitive assessment and CDB, considerable difficulties in determining eligibility of the studies were encountered due to heterogeneity in definitions and inclusion criteria used in the articles. The present systematic review aims to provide both an overview of this terminological and methodological heterogeneity and suggestions for better future research practices. A systematic review of definitions used in (N=30) studies employing psychological assessment of people with CDB served as a sample of the scientific literature on DB and CDB. Absent or heterogeneous definitions and inclusion criteria regarding both DB and CDB are evident in the sample. Fifty percent of the studies reported no definition of DB and 76.7% reported no definition of CDB. Main discrepancies are: (1) medical/functional versus ability/functioning definitions regarding DB; and (2) different criteria for onset of DB in the case of defining CDB (e.g. age versus developmental level). The results of this study call attention to a scientifically inadequate approach to the study of DB and CDB. Findings indicate that clear guidelines for sample descriptions of the DB and/or CDB populations are needed. It is suggested that studies including DB and CDB participants provide the following information: definitions of DB and CDB used; severity of sensory impairments; level of sensory ability in relation to mobility, access to information, and communication; age at onset of DB; and communication as well as language ability at onset of DB.