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Peripheral Refraction in Emmetropic Chinese Children

Purpose: Although the status of peripheral relative refraction is indicative to myopia development in animals, this is yet to determine in humans. The aim of the study was to provide baseline data in emmetropic children.

Methods: 117 children (age:11.3±2.1 years) with emmetropic central refraction (0.04±0.28D) were included. The peripheral refraction was measured under cycloplegia by a Hartmann-Shack wavefront sensor (VPR, Voptica SL, Spain). This instrument allows to measure fast in horizontal visual field from temporal 30° to nasal 30° with an interval 1°. We analyzed the refraction results to consider the presence of peripheral astigmatism. The relative position of the circle of least confusion to individual retina positions was obtained by decomposing to horizontal and vertical power respectively using the formula: PHV=S+0.5C(sinA-cosA) , where S is the spherical power, C the cylindrical power and A the axis of the astigmatism. A positive PHV value indicates the focal plane is behind the retina (H), while a negative value indicates in front of the retina (M). A PHV between -0.25D to + 0.25D was regarded as within the retina (W). In addition, peripheral refraction in other meridians (from superior 20° to inferior 16° with a vertical interval of 4°) was measured in 87 out of the samples. A 2D map of the pan-retinal refraction was then produced for each subject and the average SER of each quadrant was compared by paired-t test.

Results: We found a large variability in peripheral refractions among subjects despite their quite homogeneous central refraction and age range. To better classify the results, the peripheral refraction profiles were categorized into 9 types: HH, WH, HW, HM, MH, MW, WM, WW, MM. The percentage of each category was : 33.9% for HH, 11.8% for WH, 8.5% for HW, 6.7% for HM, 16.9% for MH, 6.7% for MW, 5% for WM, 5% for WW, 5% for MM. In the cases with 2D maps, it was found that there was no significant difference between temporal and nasal average SER (-0.09±0.35D vs -0.1±0.35D, P=0.693), while the superior retina was significantly more myopic than inferior one (-0.2±0.40D vs 0±0.34D, P<0.001).

Conclusions: Emmetropic Chinese children presented quite varied patterns of peripheral refractions. The most common type of refraction profile was HH (33.9%), and the least common types were WW (5%) and MM (5%). This will serve as a basis for future longitudinal study to decipher the relationship of peripheral optics and myopia.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 – May 2, 2019.

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