Visual function in very low birth weight adolescents : fifteen-year follow-up of children in southeast Sweden

Abstract

Background: Very low birth weight (VLBW < 1500 g) carries an increased risk of visual and cognitive deficits. Long term follow-up studies are sparse. The associations between neural structure and visual and cognitive outcome need to be more fully explored.

Aims: To describe visual functions in adolescents with VLBW in comparison with a matched control group and to investigate associations with white matter damage of immaturity (WMDI), optic disc measurements and cognitive functions in the VLBW group.

Subjects (Papers I-III): A total of 86 VLBW children survived the neonatal period during a 15 months period in the southeast region of Sweden. Fifty-nine of those, and 55 term control infants, participated in the 15-year follow-up study. (Paper IV): A subgroup including 18 VLBW subjects and 29 control subjects participated.

Methods: Structural assessments included brain MRI, digital analysis of fundus photographs and cycloplegic refraction. Functional evaluations comprised best corrected visual acuity, stereo acuity, visual fields, ocular alignment, fixation behavior, cognitive visual problems and intellectual level.

Results: Twenty-eight percent of the VLBW subjects had WMDI. The mean neural retinal rim area was smaller - in normal sized optic discs - in the VLBW than in the control group (p=0.018). The VLBW adolescents had more tortuous retinal arterioles than the controls (p<0.001). Astigmatism was more frequent in the VLBW group (19%; p=0.001). Significant differences between the groups were found, to disadvantage of the VLBW subjects, regarding visual acuity, stereo acuity and visual fields. Ocular misalignment, including heterotropia and heterophoria, was more common in the VLBW group (22%; p=0.004). The VLBW subjects had more horizontal vergence instability than the control subjects (p=0.035). The structured history revealed higher rates of cognitive visual problems in the VLBW group, in particular within depth, simultaneous, spatial orientation and motion perception. Intelligence quotients including full scale IQ, verbal subtests and performance subtests were significantly lower in the VLBW group. WMDI was significantly associated with visual field sub normality, myopia, ocular misalignment, vergence instability and cognitive visual problems. Subnormal results of performance subtests were associated with decreased visual and stereo acuity, ocular misalignment, vergence instability and cognitive visual problems.

Conclusion: This study confirms previous observations that adolescents with VLBW are at a disadvantage regarding visual and cognitive outcome compared with adolescents with normal birth weight. Adolescents with WMDI had more pronounced visual and cognitive dysfunction.