The majority of children with DS (60%) were found to have negative
(spherical aberration)
compared with only 14% of the controls. The
data also showed a negative trend with increasing magnitudes of the RMS of combined total HOA, in contrast to the positive trend shown by the results of the control group. Studies reporting HOA among populations of children and adults typically report spherical aberration
to be positive, between 0.04 μm and 0.06 μm over a 5-mm pupil,
22,29,41 in agreement with the average results of the control group. The more negative
present within the DS group is contradictory to what one might have expected for eyes that have been reported to have steeper than average corneae
42 and for individuals with greater amounts of hyperopia.
29 The more negative ocular spherical aberration in the DS eyes may therefore reflect differences in internal spherical aberration and relate to the shape of the crystalline lens. An increase in negative internal spherical aberration, which would overcompensate for positive corneal spherical aberration, is consistent with a flattening of the posterior surface of the crystalline lens (Marcos S, et al.,
IOVS 2002;43:ARVO E-Abstract 1510). Haugen et al.
6 reported a flatter anterior surface of the crystalline lens amongst the eyes of participants with DS compared with healthy controls; however there are currently no data reporting posterior lens shape in DS. One could hypothesize that a flatter crystalline lens in the DS eye in conjunction with negative
could provide an atypical stimulus cue for accommodation and may help to explain the poorer accommodative function commonly found in individuals with DS
2,10,11 Further investigation of the crystalline lens including density and refractive index gradient
43,44 and of peripheral cornea shape
42 in DS may help to explain the presence of negative spherical aberration found in this group.