As outlined in Chap. 2, a large proportion of the information concerning our physical and social worlds is processed in the visual system (Goldstein 2010; Yantis 2013). The close integration with cognition, language, emotion, motivation and the motor systems, as well as the importance of visual information for these functional systems, also means that visual impairment can affect them. Thus, the normal development of vision depends on the corresponding development of cognitive, linguistic, emotional, motivational and motor capacities, and vice versa (see also Chap. 3); hence, visual perception, cognition and mental capacities are closely associated.

Visual disorders can have different consequences for mental and motor functions; often, children with CVI show combined impairments in vision, cognition, social-emotional and motor difficulties; the exact proportion of children with cerebral palsy who have CVI is unknown, but may be in the region of 60–80 % (Mervis et al. 2002; Venkateswaran and Shevell 2008; Barca et al. 2010). In everyday life, visual impairment may cause difficulties with finding a particular toy on a patterned floor or in a toy box, with learning to read, with recognising people or finding the way (Dutton 2009). Thereby, aetiology, severity and extent of brain injury or brain dysfunction play a crucial role: the more brain structures affected, typically, the more severe the resulting disability, vision impairment included (van den Hout et al. 1998). In children with PVL, CVI is typically associated with cognitive impairment (Jacobson et al. 1996). Additional functional impairments may not only exaggerate the degree of visual disability but perhaps also impede spontaneous improvement (Bonnier et al. 2007; Tadic et al. 2009) or improvement following treatment and require greater effort to manage, particularly if cognition and motivation and mood are affected. Cioni et al. (2000) have found that in children with PVL the degree of visual impairment correlates significantly with the child’s general development; nearly all Griffiths developmental subscales (hearing and talking, motor functions, eye-hand coordination) showed moderate to high correlations with the degree of visual impairment. In addition, CVI has been shown to be a significant predictive factor for a child’s further development. The same interdependency has been found in children with hypoxic-ischaemic brain injury (Mercuri et al. 1999). The higher the degree of visual impairment at the age of 5 months, the more pronounced the delay in development in the motor domain, and for general development, by the age of 3 years. Table 5.1 shows the rates of visual and nonvisual impairments in a group of 30 children with perinatal brain injury, who were assessed at the age of 6–15 years. Although this group is small, the data can be taken as evidence, that the combination of visual impairment and at least one additional dysfunction in the cognitive, motor or language domain, is the rule, i.e. most children with CVI suffer from dysfunction in another functional domain.

Developmental trajectories of children with CVI differ, in particular qualitatively, from those of children with normal development (van Braeckel et al. 2010); moreover, developmental differences may increase with increasing age. In addition, children with early brain injury more frequently exhibit (~60 %) psychopathological symptoms compared to children with normal development in the sense of an increased psychological vulnerability (Spreen et al. 1995). However, as Stiers and Vandenbussche (2004) have reported, children with CVI may also show normal cognitive development.

In conclusion, CVI can influence nonvisual functional systems in an unfavourable way and can cause secondary functional impairments. However, in cases of combined dysfunction, it is important to also differentiate between primary and secondary impairments in the nonvisual domains. In the following sections, interactions between vision and nonvisual domains and secondary effects of CVI on these domains are described in more detail.

Visual disorders can impair development of direction and maintenance of attention, both externally triggered and by intention (Cavezian et al. 2013). Intentional guidance of attention depends on prior visual experience of objects, faces, scenes, etc. If visual-spatial appreciation is insufficient, visual attention cannot be accurately shifted to locations in space that contain relevant information. Attention can, however, also support vision and gaining of visual experience. Children with impaired but still useful vision often engage attention and perceptual learning highly efficiently and develop special strategies to enhance capture of visual information by attention. The price for this higher engagement of attention is fluctuating concentration and earlier and more rapid onset of fatigue, along with greater expenditure of time. These impairments in attention are typically associated with reduced visual performance thereby accentuating the features of CVI (Das et al. 2007).

If visual information cannot be processed accurately and completely, stored information in visual memory is incomplete and inaccurate and may even be false, as is the experience gained; use of vision for action will cogently be less successful. Examples of effects of visual impairment on visual memory include difficulties with identifying and recognising landmarks for visual-spatial/topographical orientation, or incomplete or incorrect drawing of objects from memory (Dutton 2002). For the acquisition of reading skills, learning of an efficient strategy of text processing is essential, including optimal eye movement patterns for reading. If, however, letters and words cannot be processed accurately (see Sect. 4.​3.​9), the development of an efficient reading strategy will be impaired (Fellenius et al. 2001).

Executive functions also need visual information for the execution of superordinate functions for the guidance of behaviour, for monitoring and controlling, and for flexible adaptation to changes in the stimulus and task conditions (see Sect. 3.​3). In the presence of visual impairment, executive functions cannot develop and operate properly (Tadic et al. 2009) unless supplementary or compensatory skills are developed and employed.

In language development, assigning names (labels) to visual stimuli, e.g. forms, figures, colours and objects, but also animals, flowers, faces and places may be difficult and inaccurate, if visual stimuli are not processed and identified correctly. The same problem applies to spatial directions and references (e.g. left-right, up-down, forwards-backwards). Furthermore, learning to read may also be impaired in children with CVI (see Sect. 4.​3.​9). This is exemplified in children with PVL (see Sect. 4.​5.​3), who may have low visual acuities but also may have difficulties with discrimination of symbols and letters presented in a line (Pike et al. 1994) and (as mentioned above) difficulties due to visual crowding. Possibly, impaired organisation and guidance of eye movements in text processing (e.g. oculomotor apraxia; see Sect. 4.​4) may additionally render learning to read difficult (Lanzi et al. 1998). The probability that children with this combination of visual and oculomotor disorders will be able to learn to read depends crucially on their verbal intelligence, their verbal memory capacity and their attentional and executive capacities (Fellenius et al. 2001; Sireteanu et al. 2006; Menghini et al. 2010; Vidyasagar and Pammer 2010). Thus, successful acquisition of reading requires visual, oculomotor, perceptual, cognitive and linguistic capacities, which have to interact in an optimal way; any dysfunction in one of these domains, or their interplay, can impair reading acquisition. In children who cannot interpret written symbols, despite being able to pronounce, identify and put letters together to synthesise words by sound, reading of print may be unattainable (Jacobson and Dutton 2000).

Correct identification of affective (social) signals is essential to ‘read’ emotions of other people (social perception; see Sect. 2.​3.​10). Impaired vision can affect social perception and can influence social behaviour, which depends on social perception. As a result, social responses may be inadequate or even absent, which may be interpreted as missing or defective social understanding (empathy) or lack of social interest, i.e. as an affective disorder. If social experience is limited in the way described, the risk of developing inadequate social behaviour in the long term may be increased, and persistent psychopathological symptoms may develop (Max et al. 1998). It is our experience that children, whose lack of vision is recognised, understood, handled optimally and not criticised, are least likely to manifest such difficulties.