Very preterm-born children are at risk of damage to both peripheral and central structures of the visual system. Retinopathy of prematurity (ROP) accounts for the highest rates of ocular morbidity in very preterm survivors, but visual dysfunctions are also present in very preterm children without ROP. Abnormalities in brain development result in reduced brain volumes and disturbed integrity of cerebral white matter. Consequently, cerebral visual impairments have been recognized as a major cause of visual impairment among preterm-born children and may occur when the central structures of the visual system are affected.
Large cohort studies report visual sensory deficits in very preterm children, including ocular misalignment and reduced visual acuity, contrast sensitivity, and stereovision.[4, 5] In addition, a recent meta-analysis showed that visual perceptive dysfunctions are most prominent on tasks requiring visual-spatial analysis. It is, however, unclear whether visual perceptive dysfunctions exist either independently or as a result of visual sensory deficits.
Visual perceptive abilities have recently been identified as one of the neurocognitive factors underlying the well established IQ differences between very preterm and term-born children. In addition, weaker fine and gross visual-motor skills,[4, 5] reading problems and academic underachievement in very preterm children are associated with visual sensory and perceptive dysfunctions.
The aims of this study were to (1) establish a comprehensive profile of visual functioning by extending routine sensory vision screening with visual perceptive measures, (2) exploring the association between visual sensory and perceptive dysfunctions, and (3) exploring the association between visual abilities and intellectual functioning.
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This study compared visual sensory and perceptive functions between VP/VLBW children and term children, and explored associations between sensory and perceptive dysfunctions, and between visual functions and intelligence. We found a higher percentage refractive errors, and visual sensory dysfunctions in VP/VLBW children than in term children, including medium sized effects for visual acuity, stereovision, and inferior visual field, consistent with previous studies.[4, 5] Inferior visual field impairment has been associated with cerebral white matter damage in VP/VLBW children. Visual sensory deficits occurred more often in VP/VLBW children with severe cranial ultrasound abnormalities or ROP, consistent with existing evidence. Visual perceptive dysfunctions in VP/VLBW children were indicated by small to medium effects for Position in Space performance and static coherence sensitivity. Weaker visual-spatial analysis as indicated by the Position in Space subtest agrees with results in a recent meta-analysis. Similar to existing evidence,[25, 26] we found decreased mean static coherence sensitivity in VP/VLBW children, but no evidence of a group difference for motion coherence sensitivity was seen. Weaker motion coherence processing has been found in studies that included smaller samples of older VP/VLBW children,[25, 27, 28] but differences in stimulus configuration may also have caused contradicting findings across studies.[25, 27]
Associations between visual sensory and perceptive dysfunctions were small sized. Only one in three VP/VLBW children with perceptive deficits would have been detected if routine vision screening relies on visual sensory measures, suggesting that routine vision screening should also include visual perceptive tests. Visual sensory and perceptive abilities, each, explained small amounts of variance in VIQ. Interestingly, visual perceptive measures only significantly contributed to the medium sized association with PIQ. In addition to the study that identified visual-spatial abilities among a set of neurocognitive abilities to fully account for IQ differences between VP/VLBW and term children, our results suggest differential effects, favoring a relationship between visual perceptive abilities and PIQ. Specifically, visual perceptive functioning and PIQ both draw on abilities such as discriminating visual reversals and rotations and might share neural networks, including posterior-frontal white matter association tracts and the medial temporal region.[29, 30]
Neural correlates underlying visual dysfunctions in VP/VLBW children are scarcely studied. A specific dorsal stream vulnerability in VP/VLBW children has been suggested, referring to impaired functions of the dorsal visual processing stream (i.e. visual-spatial analysis, motion perception, and unconscious control for visual-motor action). Our results confirm weaker visual-spatial performance, as indicated by the Position in Space test, but we did not demonstrate impaired motion-related perception. In addition, it should be noted that static and motion coherence sensitivity have been shown to rely on dorsal as well as ventral steam functioning.
This study has some limitations. Because of non-cycloplegic video refraction, refractive errors were not detected reliably. Prescribed glasses and current referrals for refractive assessment were used as measures of refractive error instead, and potential adverse effects on visual functioning were evaluated. Besides, reduced visual functions have also been found in VP/VLBW children with adequate refractive correction. Measures of oculomotor functioning, contrast and stereovision may have lacked sensitivity to detect subtle dysfunctions. Reduced sensitivity has possibly led to a low incidence of deficits and, consequently, limited power to detect group differences. Nonetheless, our assessment has been consistent with commonly used tests in clinical (sensory) vision screening of young children and our results indicate that the sensitivity of such tests to detect visual perceptive dysfunctions is very limited. Furthermore, color vision testing based on pseudoisochromatic plates using basic shapes could be more appropriate. The distinction between visual sensory and perceptive measures might be seen as arbitrary, but is consistent with the distinction between ophthalmic and neurocognitive assessments, respectively. Impaired attention functioning might be associated with visual as well as intellectual development, but attention deficits seem unlikely to account for the specific profile of visual deficits that we found.
In conclusion, we found evidence for visual sensory and perceptive dysfunctions in VP/VLBW children compared with term children that occurred independently of each other. In addition, visual perceptive abilities showed a medium sized association with PIQ, in contrast to a small sized association with VIQ. Future studies should investigate factors underlying the associations found, including visual attention dysfunctions, and identify opportunities for intervention.