Peripheral Refraction and Eye Lengths in Myopic Children in the Bifocal Lenses In Nearsighted Kids (BLINK) Study

Abstract

Purpose: Provide a detailed assessment of peripheral refractive error and peripheral eye length in myopic children.

Methods: Subjects were 294 children aged 7 to 11 years with -0.75 to -5.00 diopter (D) of myopia by cycloplegic autorefraction. Peripheral refraction and eye length were measured at ±20° and ±30° horizontally and vertically, with peripheral refraction also measured at ±40° horizontally.

Results: Relative peripheral refraction became more hyperopic in the horizontal meridian and more myopic in the vertical meridian with increasing field angle. Peripheral eye length became shorter in both meridians with increasing field angle, more so horizontally than vertically with correlations between refraction and eye length ranging from -0.40 to -0.57 (all P < 0.001). Greater foveal myopia was related to more peripheral hyperopia (or less peripheral myopia), shorter peripheral eye lengths, and a consistent average asymmetry between meridians.

Conclusions: Peripheral refractive errors in children do not appear to exert strong local control of peripheral eye length given that their correlation is consistently negative and the degree of meridional asymmetry is similar across the range of refractive errors. The BLINK study will provide longitudinal data to determine whether peripheral myopia and additional peripheral myopic defocus from multifocal contact lenses affect the progression of myopia in children.

Translational relevance: Local retinal control of ocular growth has been demonstrated numerous times in animal experimental myopia models but has not been explored in detail in human myopia development. These BLINK baseline results suggest that children's native peripheral optical signals may not be a strong stimulus for local growth responses.

Keywords: contact lenses; myopia; peripheral refraction; refractive error.

Figure 1

(A) The experimental setup including the custom headrest to allow for rotation of a child's head in order to maintain fixation in primary gaze and the cutouts on the side to allow for targets at 40° eccentricity to be seen. White arrows point to the front-silvered mirrors for measurement of vertical peripheral refraction. (B) The appearance of the pupil with fixation at 40° eccentricity. The autorefractor is centered within the elliptical pupil without obstruction by the iris. (C) Schematic diagram of mirror placement within the autorefractor housing and angles to the illuminated targets placed on the wall at 1.5 m for 20° superior and inferior gaze and 30° superior gaze. Targets were beyond the rim of the autorefractor housing and not visible to the subject without the use of the mirrors (striped rectangles). For 30° inferior gaze, subjects fixated a target placed within the hood of the autorefractor in order to avoid a mirror obscuring its camera aperture. The autorefractor would be translated and re-focused during peripheral refraction to maintain alignment with the center of the entrance pupil.

Figure 2

Plots of both absolute and relative peripheral refraction (A) and absolute and relative peripheral eye length (B) in the horizontal meridian and absolute and relative peripheral refraction (C) and absolute and relative peripheral eye length (D) in the vertical meridian. Error bars represent the standard error of the mean. The best-fit parabola is shown for each. The equations for horizontal peripheral refraction and eye length, respectively, are y = 0.0012 x² + 0. 0009 x − 2.57 and y = −0.00059 x² − 0.0056x − 24.44. The equations for vertical peripheral refraction and eye length, respectively, are y = −0.00054 x² + 0.0008 x − 2.44 and y = −0.00040 x² − 0.0026x − 24.49. Each term is significantly different from 0 (P < 0.001) except for the linear term for peripheral refraction. The model R² was computed by squaring the correlation between predicted and observed values.

Figure 3

Plots of quadratic coefficients fit to subject-level data as a function of central spherical equivalent refractive error for peripheral refractive error (RPR) and peripheral eye length (RPEL). The horizontal meridian is represented by the plus (+) symbols and the vertical by the open circles (o). The equations for the best-fit regression lines for peripheral refraction in the horizontal and vertical meridians, respectively, are y = −0.00015x + 0.00080 (R² = 0.05) and y = −0.00013x − 0.00086 (R² = 0.02). The equations for the best-fit regression lines for peripheral eye length in the horizontal and vertical meridians, respectively, are y = 0.000044x − 0.00048 (R² = 0.05) and y = 0.000056x − 0.00026 (R² = 0.07).

Figure 4

Relative peripheral refractive error in the sagittal and tangential meridians as a function of eccentricity and meridian: horizontal (A) and vertical (B). Error bars (some obscured) represent the standard error of the mean.