Because it involves the interaction of hearing and vision impairments, so-called 'deafblindness' creates unique challenges that go beyond those of each condition alone. When both senses are impaired, the usual compensatory methods no longer work, resulting in more complex communication and accessibility barriers.
The definition of deafblindness varies greatly between countries, leading to wide differences in recognition and services. "Quebec offers rehabilitation services specifically for deafblindness, but in some countries the condition isn't recognized, leaving families to bear the full burden," said Walter Wittich, a professor in the School of Optometry at Université de Montréal.
The idea of recognizing deafblindness as a single impairment originated in Europe, led by a politician with a deafblind child. "While trying to find health services for his daughter, he experienced first-hand the difficulties in accessing services adapted to simultaneous hearing and vision loss," Wittich said. "So he decided to put the issue on the international political agenda."
Criteria to standardize understanding
In 2001, the World Health Organization created the International Classification of Functioning, Disability and Health (ICF), a set of criteria designed to standardize how we understand health and disability, and to determine how a condition impacts an individual's functioning and participation in daily life.
"It is a biopsychosocial model that provides a framework for thinking about health conditions beyond medical treatment," explained Wittich.
The ICF framework includes over 1,400 individual categories, or codes, which describe an individual's functioning in all possible areas. "In theory, we not only can use this type of coding to describe an individual, but also turn it around and create a system of codes for an illness," he explained.
By creating a common, universal set of criteria, these codes help overcome language and cultural barriers, making it easier to recognize the challenges posed by deafblindness. "It means I can easily collaborate with researchers and professionals anywhere in the world because we all use the same codes," Wittich said.
A core set of codes
Having so many codes makes the ICF complex and impractical for use in many contexts, such as clinical settings and policymaking. To address this, experts typically develop a subset of codes, or core set.
Recently, such a core set was developed for deafblindness by an international multidisciplinary team under Wittich's scientific direction. The process is described in a paper published in March 2025 in the British Journal of Visual Impairment.
As required by the WHO, the process comprised four stages: 1) a systematic literature review to identify research priorities; 2) qualitative interviews with individuals living with deafblindness; 3) an online survey of professionals who work with deafblind people, including ophthalmologists, nurses and interpreters; and 4) integration of the clinical perspective by examining scenarios for evaluating services.
"At every stage, we gathered input and perspectives from experts around the globe," said Wittich. "It was truly a monumental undertaking."
Four years of work
All of the codes identified as relevant to deafblindness were then presented at a consensus conference in Spain in October 2024. Ultimately, the four years of work produced three core sets, each with a different number of codes.
The comprehensive core set (218 codes) is a list of categories that covers the typical spectrum of functioning problems affecting people with deafblindness, making it useful for policymaking and legislation. "It can be used, for example, to justify coverage of services by a public or private health insurance plan," explained Wittich.
The medium core set includes the basic codes needed for interprofessional clinical communication, while the brief core set (33 codes) focuses on the essential elements of functioning and impairment to consider when working with an individual in a clinical setting.
As this first effort comes to a close, Wittich is embarking on a similar initiative, this time focusing on children and youth (under 18) affected by deafblindness.
"The causes and impacts of deafblindness are very different for children than for adults with acquired deafblindness, so it makes sense to develop a core set specifically for this group," said Wittich. He also hopes to develop a core set for deafblind people who communicate using sign language, and then another for those aged 60 and over.
'Long underrepresented in research'
Wittich also hopes that the unique perspectives of deafblind individuals will finally be heard and taken into account. "Deafblind people have long been underrepresented in research," he said.
Several factors have contributed to their invisibility. First, communication is more complex, since many deafblind individuals do not learn to read or write, and interpreters are relatively scarce. Additionally, deafblind individuals often have to fight to be included in decision-making instead of having others decide for them.
"Since I am not deafblind myself, I have had to work to build trusting relationships with the deafblind people on my team," Wittich said.
Now, he added, thanks to the ambitious international initiatives he helps lead, clinicians and policymakers will be able to provide services truly tailored to the needs of people living with deafblindness.
According to the Brussel-based World Federation of the Deafblind, between 0.2 and 2 per cent of the global population - as many as 165 million people - have some degree of both blindness and deafness.
About these studies
"The WHO ICF comprehensive Core Set for deafblindness: a narrative overview of the development process," by Walter Wittich and Shirley Dumassais, was published March 4, 2025 in the British Journal of Visual Impairment.
"Development of the International Classification of Functioning, Disability and Health Core Sets for children and youth with deafblindness: protocol for a multistudy collaboration across regions of WHO," by Walter Wittich and Shirley Dumassais, was published April 7, 2025 in BMJ Open.
