The sibling relationship is unique because it is often the longest-lasting bond within a family, sometimes lasting a lifetime (McHale et al., 2012; Travers et al., 2020; Erdem et al., 2024). It has been described in literature as an attachment bond (Buist et al., 2013; Shenoy et al., 2024), which has characteristics of both reciprocal (e.g., peer-like) and complementary (e.g., parent-child like) interactions (Kinsley et al., 2025; Howe et al., 2022).

In childhood, the sibling bond is the first bond between peers with the peculiarity that they do not choose each other voluntarily unlike friends. Their bond spans both physical and social environments, especially in childhood. In fact, siblings share much of their time in daily interactions, making this time a unique source and context for learning, for developing socio-cognitive skills and for mutual social support (Edels et al., 2024; Howe et al., 2018, 2022; Shenoy et al., 2024).

The sibling relationship is therefore crucial in their lives, as it significantly influences their development, creating a common history and mutually molding their behavior, attitudes, and psychological functioning (Buist et al., 2013; Howe et al., 2022; Edels et al., 2024). The quality of this relationship is influenced by the individual differences of each sibling, by family dynamics, characteristics and by environmental context, which all contribute to the mental health of both siblings and, consequently, also to their quality of life (QoL; McHale et al., 2012; Incledon et al., 2015; Shojaee and Alizadeh, 2019; Hayden et al., 2023; Rawat and Malik, 2024).

The outstanding value of siblings' relationships in children is widely described in literature, even in the presence of a disability in one of the siblings (Fisman et al., 1996; Vella Gera et al., 2021; Williams et al., 2024). In the International Classification of Functioning, Disability and Health (World Health Organization, 2001), disability is a multi-dimensional concept which is defined as functioning of a person in multiple life areas and the result of interaction between the person's health condition and that person's contextual factors, specifically environmental factors and personal factors; World Health Organization, 2001). The presence of a developmental disability in one of the children can have a substantial impact on the family environment, contributing to a wide spectrum of both positive and challenging effects in the siblings (Simeonsson and McHale, 1981; Fisman et al., 1996; Rossiter and Sharpe, 2001; Veerman et al., 2023; Cooke et al., 2024). Siblings may experience feelings of love and pride and develop greater maturity, responsibility, and empathy (Shivers, 2019; Vella Gera et al., 2021; Martinez et al., 2022). They may also experience feelings of sadness, anger, jealousy, guilt, worry and embarrassment (Caliendo et al., 2020; Vella Gera et al., 2021; Martinez et al., 2022; Shenoy et al., 2024), as well as more internalizing and externalizing problems (Fisman et al., 1996; Buist et al., 2013; Martinez et al., 2022). Nonetheless this sibling relationship maintains its characteristics of uniqueness and long-life duration, profoundly influencing their lives. McHale et al. (2012) provided evidence on how siblings profoundly influence each other's development in childhood and adolescence, building on the foundations of research on siblings' relationships. This line of research draws on Adler's theory about the importance of siblings' dynamics for their psychological adjustment, on learning theories in which siblings are role models for each other in their development, and on cross-cultural perspectives that highlight what is universal in the experience of being siblings and what is instead shaped by culture and the specific context in which an individual grows up. Already in 1983, Dunn affirmed the uniqueness of the sibling relationship because it includes both complementary interactions of the child-adult relationships and reciprocal and mutually influential dynamics typical of the peer relationship. Furthermore, the high level of social interaction between siblings, which is also emotionally intense, acts as a catalyst for socio-emotional development (Dunn, 1983). The value of the intensity of the sibling bond, of the enjoyment from being together and of the time spent together has also been highlighted by Foley et al. (2025) in their study on neurodivergent twins. Shivers (2019) investigated adolescent siblings' self-reported empathy and feelings, showing greater perspective-taking ability related to positive feelings toward siblings in adolescents of individuals with autism compared to adolescents of typically developing siblings. Le Bouef and Dworkin (2021) explored how youth siblings are a context for positive development because, despite less daily communication during late adolescence and young adulthood, siblings remain an important source of support for each other; indeed, in their study, the frequency of sibling communication was also positively associated with emotional, social, and psychological well-being. Milevsky (2005) showed how in emerging adulthood social support provided by siblings is associated with psychological adjustment, in which siblings who received more sibling support scored higher on self-esteem and life satisfaction and lower on depression and loneliness than those individuals who received less sibling support. White (2001), in her panel analysis on nearly 9,000 adults who underwent two interviews approximately 5 years apart, examined four measures of the sibling relationship: proximity, contact, giving help, and receiving help. Her study showed how siblings' relationships change from the age of 18 to 85 years, showing a modest decline in contact and proximity in early adulthood and long-term stability with increased exchanges during old age. Thus, the relationship between siblings is maintained throughout the whole life and regains importance in old age, confirming its uniqueness in family relationships, mainly due to its social and emotional significance.

Despite the wide amount of literature on siblings' relationships, much less evidence is available in the field of vision impairment (VI), especially in the developmental age.

Vision impairment is mainly described as a condition of decreased visual function that interferes with the individual's ability to perform their activities of daily living (Lee et al., 2024). At the same time, through the lens of the neurodiversity paradigm, which views natural individual neurological differences and encourages their acceptance rather than considering them only as deficits (Foley et al., 2025; Cheng et al., 2025), VI can be considered a form of neurodivergence, which can be studied highlighting the role of social framing and social support as molders of development and mental health (Cheng et al., 2025).

In fact, VI significantly influences family and social interactions, as vision plays a crucial role in a child's neuropsychological, affective, and psychic development. Vision provides a scaffolding function from birth, promoting attachment relationships with caregivers through eye contact and affective-emotional attunement (Purpura and Tinelli, 2020; Battistin et al., 2024b) and fosters learning through imitation as well as through analytical and synthetic perceptive interaction with the environment (Caron et al., 2023; Baiardi and Battistin, 2022; Lo and Wang, 2024).

Indeed, all relationships within the family unit may face difficulties and challenges from the beginning because interactions and communication must be driven through the other senses, especially hearing and touch. Family dynamics change and family relationships adapt and shape themselves according to the characteristics and needs of the child with VI, who follows a neurodivergent developmental trajectory, needing more time for information processing because of their sensory impairment.

Therefore, VI affects all the areas of child development, particularly social and communicative skills, including identity recognition, emotional expression recognition, joint attention, and engagement in communication (Pinquart and Pfeiffer, 2014; Gui et al., 2023; Li et al., 2023), challenging their mental health and quality of life (Lanza et al., 2024; Langelaan et al., 2007).

The impact of contextual factors (i.e. age, gender, educational level, socioeconomical status, and social support) on mental health and QoL is well described in literature (Langelaan et al., 2007; Cheng et al., 2025). The recent systematic review by Cheng et al. (2025) stated that quite a few children with VI experience mental health issues, including anxiety, depression and low self-esteem (Li et al., 2023), and that these are connected to socio-environmental factors more than to the VI itself. Augestad (2017a) also showed a major prevalence of mood disorders in children and young adults with visual impairment, outlining how social support from family and friends as well as social activities have an important role in preventing mental health problems. Augestad (2017b) highlighted how social support and relationships play a role in increasing perceived self-esteem and self-concept, which are linked to wellbeing and psychological adjustment. Demmin and Silverstein (2020) indicated vision-specific distress, i.e. emotional reactions and distress to vision loss, as a robust predictor of depressive symptom severity as well as of anxiety, worry, withdrawal isolation in adults and older individuals. Enhanced social isolation, reduced QoL and increased risks of developing mental health problems have been shown also in children with VI (Li et al., 2024, 2023; Chadha and Subramanian, 2011).

Literature showed that the number of studies on the sibling relationship in children with and without VI is low. Kuld et al. (2020) found only one study focusing on siblings in their bibliometric map of the psychological well-being in children with vision impairment, despite the important contribution siblings can have on well-being (Jensen et al., 2022). Veldhorst et al. (2023) showed in their scoping review on the quality of life in siblings of children with vision impairment how both personal (such as prosocial behavior) and parental (such as family interaction and family functioning) factors are related to their QoL.

The aim of this study is to systematically review empirical studies on the relationship between siblings with and without vision impairment and to examine its characteristics in order to characterize it.

A total of 687 records were initially identified through databases searches (Figure 1). After removing 263 duplicate records, 424 articles were screened first by titles and then by abstracts for relevance. During these screening phases, 413 records were eliminated for not meeting the established inclusion criteria, and 11 were selected and assessed for eligibility. During the full-text screening, five articles were excluded for the following reasons: one was not in English (n = 1); two because of their article type (n = 2); the last two were not focused on the objective of this study (n = 2). Only 6 articles, focusing exclusively on specific aspects of siblings' relationships connected to VI, were eligible for final analysis. Two of them are our previous studies on siblings, but we state there is no conflict of interest because this study is an extension analysis of the previous ones (Battistin et al., 2024a, 2025). Another two studies were included at the end, after a further search through references of the selected studies. Finally 8 studies underwent final analysis.

We investigated the characteristics of the sibling relationship in the population of siblings of children with VI through a systematic review. The analysis of the selected articles, through the lens of neurodiversity, highlighted mainly positive characteristics regarding the quality of the bond between these siblings, including their philanthropic nature, their feelings of warmth and closeness not so different from those present in NT dyads, their increased understanding of VI, its normalization and the development of alternative communicative skills, as shown in the literature also in other neurodivergences (Foley et al., 2025; Shivers, 2019; Mandleco and Webb, 2015). These positive features may also play a role as protective factors for this bond: warm relationships have been associated in literature to sibling disclosure, emotional understanding, positive interactions with more prosocial behavior and companionship (Howe et al., 2001; Buist et al., 2013; Edels et al., 2024; Kinsley et al., 2025; Foley et al., 2025). This association between the quality of the relationship and siblings' behaviors has been suggested even in other disabilities such as intellectual disabilities (Hayden et al., 2023; Travers et al., 2020) and autism (Noreen, 2021; Walton and Ingersoll, 2012; Shivers, 2019).

At the same time, as researchers, we cannot underestimate the emotional ambivalence described by Erdem et al. (2024), the statistically significant difference in the subscale of conflict reported by Hemati Alamdarloo et al. (2019), as well as some problematic behaviors reported by Lund (2001), their positively experienced carer role and an excess of responsibility, experienced as a “good behavior” which may become over time a burden (Erdem et al., 2024; Battistin et al., 2024a, 2025), that may all be potential risk factors which must be taken into consideration by caregivers and healthcare professionals. Furthermore, the feelings of sorrow and sadness for the visual condition of their brother/sister may become a risk factor for NT siblings if they do not share them with a professional with expertise, who can support them in the processing and acceptance of the situation facing them. Indeed, Ashori (2025), who focused his study not on children but on adolescents, also found a statistically significant difference in the level of internalizing and externalizing problems compared to adolescents with NT siblings, highlighting how emotional and behavioral issues may become more evident as siblings grow older. Kef (2002) also found a slightly unbalanced siblings' relationship, in which adolescents with VI giving less social support than their TD siblings and perceiving less social support from their TD siblings than from their peers. Datta and Sabir (2021), who also interviewed parents and teachers, highlighted the fundamental role of the whole family environment in the sibling relationship.

Our findings outlined how the sibling relationship in children with and without VI is mainly a positive relationship, even if complex and multifaceted. Results indicated a coexistence of potential protective and risk factors, which may develop with age and are strictly intertwined with the daily social context in which siblings live and its supportiveness. Warmth and closeness foster bonding; nevertheless, as professionals we must not underestimate all the psychological implications, burden included, associated with being brother or sister to a ND child.

This study has also some limitations: first of all, despite the large number of articles on the sibling relationship in literature, the number of articles on the sibling relationship in vision impairment is scarce. Secondly, the studies are all cross-sectional, so future studies, in particular longitudinal, are needed to explore how the sibling relationship develops with age. Thirdly, the included studies used different methods: some of them focused on and gave voice only to NT siblings, others only listened to ND children, while it should be interesting to study dyads in order to have a perspective from all the parties involved in this relationship. On this point, collecting parents' perceptions on their children's relationships, such as in two of the selected studies, could bring added value to the discussion, as well as expanding the study also to teachers or other relevant caregivers in the social environment, such as in the study by Datta and Sabir (2021). Finally, the majority of the included articles were based on data obtained from relatively small sample sizes, so studies with larger samples are necessary.

Our findings have a clinical implication in giving information to healthcare professionals on possible interventions to highlight protective factors and to prevent the onset of risk factors. We need, as clinical professionals, to work together with close family, extended family, caregivers and teachers to promote a social environment that is inclusive and sensitive to neurodiversity, highlighting siblings' strengths, listening to their worries and facilitating them when needed. At the Robert Hollman Foundation NT siblings participate in clinical and educational activities whenever possible. This is a first useful step, even if sometimes insufficient, because they also need to share their daily experiences and feelings with expert professionals and other siblings in order to strengthen all the positive aspects of their relationships and to address their difficulties in order to prevent the possible onset of mental health disorders and to improve their daily QoL (Gladyszewska-Cylulko, 2024). (Veerman et al. 2025), (2023) showed the social validity of an intervention for NT siblings using the serious game “Broodles” to help them to become more aware of their role and to be able to share their thoughts and feelings with other individuals, both professional and non-professional.

This is a priority for us as professionals, to also consider sighted siblings‘ needs to avoid impact on their mental health and on the quality of their lives. Indeed, Kirchhofer et al. (2022) showed the great value of social support for siblings of children with neurodevelopmental disorders as a protective factor to prevent negative psychosocial adjustments, as well as internalizing and externalizing behaviors. Veerman et al. (2023) also stated how siblings of children with disabilities should be supported, although there are only a few evidence-based interventions in literature on this topic. Addressing siblings' challenges facing siblings can only happen through work on the family and social environment, promoting a culture of inclusion through accurate information that values individual differences as resources and countering stigmatization.

In conclusion, this review confirmed the paucity of literature on siblings' relationships in the field of vision impairment. These findings also give a scientific contribution because they outlined some characteristics of the sibling relationship, mostly positive, but they do not allow any conclusion of evidence to be drawn due to the very limited number of included studies, with different methods and mainly small samples. The pressing need for research on this topic has been highlighted and future studies are necessary to characterize this sibling relationship in order to identify protective and risk factors for siblings' wellbeing, mental health and for the promotion of healthy family and social relationships.