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Sara J. McCullough, Julie-Anne Little, Kathryn J. Saunders; Anomalous Wavefront Aberrations Reduce Optical Quality In Down Syndrome. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2810.
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Down syndrome (DS) is associated with ocular abnormalities and reduced visual function. Structural and functional differences in the optics of DS eyes are reported in the literature. Studies report a thinner, steeper cornea and a thinner crystalline lens and, functionally, a degrading influence of DS optics on resolution acuity. The present study further investigates optical quality in DS by comparing wavefront aberrations in DS and control eyes.
Participants were 38 children with DS (6-16 years) and 209 age-matched controls. Monochromatic higher order aberrations (HOAs) were measured following cycloplegia (1% Cyclopentolate) using Shack-Hartmann aberrometry (IRX3, Imagine Eyes). HOAs were analysed over a fixed 5mm pupil using Zernike polynomials from 3rd to 6th order. Optical quality was assessed using the Strehl ratio (calculated by the IRX3 software) over 3, 4 and 5mm pupil diameters.
HOAs were measured successfully from 73% of the DS group and 97% of controls. Right eye data were analysed. Mean root mean square of total HOAs differed significantly between groups (0.33µm±0.09 DS; 0.29µm±0.12 controls) (Mann Whitney z=-2.34, p=0.02). Mean spherical equivalent did not correlate significantly with the degree of HOAs in either DS or control groups (p>0.05). Significant differences were found between the DS and control group for trefoil sine term Z(3,-3), horizontal coma Z(3,1), spherical aberration Z(4,0), quadrafoil cosine term Z(4,4), Z(5,-3), Z(5,-1), Z(5,1) and Z(6,4). The wavefront patterns produced a significantly lower Strehl ratio in the DS group compared to controls over all pupil diameters with the greatest difference seen at 3mm (0.27±0.14 DS; 0.43±0.16 controls) (Mann Whitney z=4.84, p<0.001).
DS eyes have significantly different wavefront patterns compared to age-matched controls. These differences are unrelated to the degree of refractive error. The anomalies seen in the DS wavefront pattern contribute to reduced optical quality which could help to explain the previously reported poor visual performance noted in DS.
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