Purpose
Children from some Native American tribes are known to have elevated levels of corneal astigmatism. We report accommodation-induced changes in higher order refractive aberrations (coma and spherical aberration) among children of one such tribe, whose children participated in the tribally sponsored Tohono O’odham Vision Screening Program (TOVSP).
Methods
Children were imaged with a hand-held Shack-Hartmann Sensor, the Pediatric Wavefront Evaluator (PeWE). Children ranged in age from 6 mos to 9 yrs. Images were recorded while children watched a cartoon at 50 cm (near, n) and 2 m (distant, d) viewing distance. At least 7 focused and centered images were obtained at both fixation distances, with undilated pupil diameters ranging from 3 to 5 mm. Zernike decomposition to 4th order was performed. Lower order aberrations were converted to m, j0 and j45. Signed Zernike terms Z(3,1) (y coma, yc), Z(3,-1) (x coma, xc) and Z(4, 0) (spherical aberration, sa) were derived for the observed mm pupil diameter (mmpd). Three different pupil scaling methods were used: (1) all terms were scaled down to 3mmpd, (2) those greater than 4 mmpd scaled down to 4 mmpd (data with pupil < 4 mm excluded), and (3) all were scaled up to 5 mmpd. Within each subject, at least 3 observations were required at 4mmpd to be averaged, while 7 were always averaged at 5 mmpd and 3 mmpd. Paired sample (d and n) t-tests on the signed coefficients (micron) were compared at 3, 4, and 5 mmpd.
Results
As expected, accommodation produced a change in m from n to d of -1.33 to -0.25D (p=0.000). A small (<0.1mm) but significant decrease in d to n pd was also observed (p=0.000). J0 and J45 had small but significant differences d to n (<0.1D, p=0.000. Coma (xc and yc) did not change with accommodation (p>0.20). Spherical Aberration became increasingly negative with accommodative effort (p<0.05). Table summarizes d and n yc, xc and sa at 3 (n=545) , 4 (n=233), and 5 (n=545) mmpd.
Conclusions
In this population of Native American children, the observed coma did not change with accommodation, suggesting a non-lenticular or corneal origin. The increased negative spherical aberration with accommodation enhances near vision, and suggests a lenticular origin. Future work will compare these refractive aberrations to corneal aberrations measured with surface topography.
Keywords: 676 refraction •
463 clinical (human) or epidemiologic studies: prevalence/incidence •
684 refractive surgery: optical quality