35 Diagnostic Evaluations: Intellectual Developmental Disorder
DSM-5-TR
A diagnosis of intellectual developmental disorder according to the Diagnostic & Statistical Manual of Mental Disorders, Version 5, Text Revision (DSM-5-TR) requires impairment in one or more domains of adaptive functioning (Conceptual, Social, or Practical) in addition to low IQ. Furthermore, there must be a relationship between intellectual and adaptive deficits: “To meet diagnostic criteria for intellectual disability, the deficits in adaptive functioning must be directly related to the intellectual impairments described in Criterion A” (APA, p.38).
The challenge of evaluating adaptive functioning
Measures of adaptive functioning (e.g., ABAS, VABS) are not designed to differentiate between limitations in functioning arising from cognitive impairments and limitations arising from motor or sensory impairments. Many items on adaptive functioning measures will be inappropriate for children with motor or sensory impairments (e.g., “carries dishes to the sink” for those without the physical ability to lift dishes; “stays on sidewalk” in a child who is pushed in a wheelchair, “wipes up own spills” in a child who is not able to see the spill).
In addition, skills may develop at different times in blind and low vision children. A child who is blind will need to learn special skills to identify coins and keep track of different denominations of paper money. Thus, they are likely to learn this skill at an older age compared to a sighted child. Blind and low vision students with intact cognitive functioning are more likely than their sighted peers to be rated lower in adaptive functioning (Greenaway, et al., 2017). The difficulties are most pronounced in children with the more severe to profound visual impairment, though those with mild impairment also show difficulties relative to sighted peers (Bathelt et al., 2019).
The DSM-5 recognizes that scores are not the only consideration in evaluating adaptive functioning: “Adaptive functioning is assessed using both clinical evaluation and individualized, culturally appropriate, psychometrically sound measures… Additional sources of information include educational, developmental, medical, and mental health evaluations. Scores from standardized measures and interview sources must be interpreted using clinical judgment” (DSM-5, p.37). It is important to carefully consider all aspects of your assessment, and not rely too heavily on standardized measurements.
It is still important to use standardized measures of adaptive functioning. A standardized measure of adaptive functioning is best completed using an interview format (e.g., Vineland interview). If adaptive functioning is done in an interview format, you will better be able to understand which supports are in place due to motor or sensory impairments. Look at the manual for the adaptive functioning measure. Typically, the manuals will suggest that if a child is not capable of doing something due to a physical or sensory condition, the item must be scored as “0” but that you should take this into account in your interpretation. Do allow for a child’s use of sign language, braille, or adaptive equipment to communicate (if used independently and unprompted). This includes listening to audiobooks and screen readers for blind and low vision students (VABS-3 Manual, p.45). The ABAS manual does not discuss this topic, but a similar approach between the tests would be appropriate.
The challenge of measuring IQ
Standard IQ tests were not developed for use with blind and low vision children. For most tests (e.g., WISC-5) children with uncorrected visual impairments were excluded from the standardization sample, and are not included as a special group.
One of the reasons measurement of IQ can be challenging is that differences in concept development can impact performance on verbal IQ tasks. Furthermore, evaluation of verbal IQ can be particularly challenging in students who are English Language Learners or who have primary communication challenges. Some students are able to complete visual IQ tests, though in general these should be considered a minimum estimate of functioning.
Recommendation
When evaluating blind and low vision children, it is wise to be cautious about diagnosing intellectual developmental disorder. Be especially cautious in giving a diagnosis in young children. Sometimes there is a very clear case of intellectual developmental disorder, and in that case, a diagnosis should be made. For other students, it can be helpful to monitor their functioning over time, to see the progress they make with supports and intervention.
References
American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.). https://doi.org/10.1176/appi.books.9780890425787
Bathelt, J., de Haan, M., & Dale, N. J. (2019). Adaptive behaviour and quality of life in school-age children with congenital visual disorders and different levels of visual impairment. Research in Developmental Disabilities, 85, 154–162. https://doi.org/10.1016/j.ridd.2018.12.003
Greenaway, R., Pring, L., Schepers, A., Isaacs, D. P., & Dale, N. J. (2017). Neuropsychological presentation and adaptive skills in high-functioning adolescents with visual impairment: A preliminary investigation. Applied Neuropsychology. Child, 6(2), 145–157. https://doi.org/10.1080/21622965.2015.1129608.
