Higher order aberrations in children with Down syndrome.

PURPOSE: Down syndrome (DS) is associated with ocular abnormalities and reduced visual function. Studies report atypical optical structures in the DS eye such as thinner, steeper corneae and thinner crystalline lenses and, functionally, a degrading influence of the optics on acuity. This study further investigates optical quality in DS by comparing higher order ocular aberrations (HOAs) in DS and control eyes.
METHODS: Participants were 44 children with DS (6-16 years) and 209 age-matched controls. All participants were free from corneal or lenticular pathology. HOAs were measured following cycloplegia using Shack-Hartmann aberrometry. HOAs were analyzed over a 3-mm and 5-mm pupil using Zernike polynomials from third-sixth order. Optical quality was explored using Visual Strehl ratios (VSX) and equivalent defocus values.
RESULTS: HOAs were measured successfully from 68% of the DS group and 95% of controls. Root mean square of total combined HOAs, third, and sixth orders and coma were significantly greater in the DS group (P < 0.005). Significant differences were found between groups for Zernike coefficients Z3(-3), Z3(3), Z0(4), (P < 0.013). VSX and equivalent defocus values indicated significantly poorer optical quality in DS eyes (P < 0.02).
CONCLUSIONS: Children with DS have greater HOAs and reduced central optical quality compared with typically developing children. Whilst the differences in HOAs between the groups reached statistical significance, they were not of pathological proportions and the DS eye maintains relatively good optical quality considering the degree of ametropia and atypical optical structures often found amongst these children. The subtle reduction in optical quality may, however, compound the visuocortical deficits previously reported in DS.