Measuring visual acuity and spherical refraction with smartphone screens emitting blue light

Introduction A periodical self-monitoring of spherical refraction using smartphones may potentially allow a quicker intervention by eye care professionals to reduce myopia progression. Unfortunately, at low levels of myopia, the far point (FP) can be located far away from the eye which can make interactions with the device difficult. To partially remedy this issue, a novel method is proposed and tested wherein the longitudinal chromatic aberration (LCA) of blue light is leveraged to optically bring the FP closer to the eye. Methods Firstly, LCA was obtained by measuring spherical refraction subjectively using blue pixels in stimuli shown on organic light-emitting diode (OLED) screens and also grey stimuli with matching luminance. Secondly, the visual acuity (VA) measured with a smartphone located at 1.0 m and 1.5 m and displaying blue optotypes was compared with that obtained clinically standard measurements. Finally, the spherical over refraction obtained in blue light with a smartphone was compared with clinical over-refraction with black and white (B&W) optotypes placed at 6 m. Results Mean LCA of blue OLED smartphone screens was −0.67 ± 0.11 D. No significant differences (p > 0.05) were found between the VA measured with blue optotypes on a smartphone screen and an eye chart. Mean difference between spherical over-refraction measured subjectively by experienced subjects with smartphones and the one obtained clinically was 0.08 ± 0.34 D. Conclusions Smartphones using blue light can be used as a tool to detect changes in visual acuity and spherical refraction and facilitate monitoring of myopia progression. (AU)

Measuring visual acuity and spherical refraction with smartphone screens emitting blue light.

INTRODUCTION: A periodical self-monitoring of spherical refraction using smartphones may potentially allow a quicker intervention by eye care professionals to reduce myopia progression. Unfortunately, at low levels of myopia, the far point (FP) can be located far away from the eye which can make interactions with the device difficult. To partially remedy this issue, a novel method is proposed and tested wherein the longitudinal chromatic aberration (LCA) of blue light is leveraged to optically bring the FP closer to the eye. METHODS: Firstly, LCA was obtained by measuring spherical refraction subjectively using blue pixels in stimuli shown on organic light-emitting diode (OLED) screens and also grey stimuli with matching luminance. Secondly, the visual acuity (VA) measured with a smartphone located at 1.0 m and 1.5 m and displaying blue optotypes was compared with that obtained clinically standard measurements. Finally, the spherical over refraction obtained in blue light with a smartphone was compared with clinical over-refraction with black and white (B&W) optotypes placed at 6 m. RESULTS: Mean LCA of blue OLED smartphone screens was -0.67 ± 0.11 D. No significant differences (p > 0.05) were found between the VA measured with blue optotypes on a smartphone screen and an eye chart. Mean difference between spherical over-refraction measured subjectively by experienced subjects with smartphones and the one obtained clinically was 0.08 ± 0.34 D. CONCLUSIONS: Smartphones using blue light can be used as a tool to detect changes in visual acuity and spherical refraction and facilitate monitoring of myopia progression.

Novel Method of Remotely Monitoring the Face-Device Distance and Face Illuminance Using Mobile Devices: A Pilot Study.

Specially developed software (app) was written for handheld electronic devices that uses the device camera and light detector for real-time monitoring of near-work distance and environmental lighting. A pilot study of this novel app employed children using tablet computers in a classroom. Measurements of face-device distance and face illuminance were obtained from two schools where tablets were used regularly. Children were divided randomly into a control group (CG) and intervention group (IG). The app was calibrated in a lab and configured to store average values every 20 seconds in a remote database. In both groups, the app recorded data only when a child's face was present in the camera image. The app darkened the screen for the IG when the face-device distance was shorter than 40 cm. The total mean face-device distance was 36.8 ± 5.7 cm in CG and 47.2 ± 6.5 cm in IG. Children in IG had to accommodate approximately 0.6 D less when using their devices. The mean classroom face illuminance was 980 ± 350 lux in School #1 and 750 ± 400 lux in School #2. The novel method of remotely monitoring and controlling the face-device distance and illuminance can potentially open new paths for myopia prevention and myopia control.

New Objective Refraction Metric Based on Sphere Fitting to the Wavefront.

PURPOSE: To develop an objective refraction formula based on the ocular wavefront error (WFE) expressed in terms of Zernike coefficients and pupil radius, which would be an accurate predictor of subjective spherical equivalent (SE) for different pupil sizes. METHODS: A sphere is fitted to the ocular wavefront at the center and at a variable distance, t. The optimal fitting distance, topt, is obtained empirically from a dataset of 308 eyes as a function of objective refraction pupil radius, r0, and used to define the formula of a new wavefront refraction metric (MTR). The metric is tested in another, independent dataset of 200 eyes. RESULTS: For pupil radii r0 ≤ 2 mm, the new metric predicts the equivalent sphere with similar accuracy (<0.1D), however, for r0 > 2 mm, the mean error of traditional metrics can increase beyond 0.25D, and the MTR remains accurate. The proposed metric allows clinicians to obtain an accurate clinical spherical equivalent value without rescaling/refitting of the wavefront coefficients. It has the potential to be developed into a metric which will be able to predict full spherocylindrical refraction for the desired illumination conditions and corresponding pupil size.

The effect of longitudinal chromatic aberration on the lag of accommodation and depth of field.

PURPOSE: Longitudinal chromatic aberration is present in all states of accommodation and may play a role in the accommodation response and the emmetropisation process. We study the change of the depth of field (DOFi) with the state of accommodation, taking into account the longitudinal chromatic aberration. METHODS: Subjective DOFi was defined as the range of defocus beyond which the blur of the target (one line of optotypes of 0.1 logMAR shown on a black-and-white microdisplay, seen through different colour filters) was perceived as objectionable. The subject's eye was paralysed and different, previously-measured accommodative states (corresponding to the accommodative demands of 0D, 2D and 4D) were simulated with a deformable mirror. Different colour conditions (monochromatic red, green and blue and polychromatic (white) were tested. The DOFi was measured subjectively, using a motorised Badal system. RESULTS: Taking as reference the average accommodative response for the white stimulus, the blue response exhibits on average a lead of 0.45 ± 0.09D, the green a negligible lead of 0.07 ± 0.02D and red a lag of 0.49 ± 0.10D. The monochromatic DOFi, calculated by averaging DOFi over the red, green and blue colour conditions for each accommodative demand was 1.10 ± 0.10D for 0D, 1.20 ± 0.08D for 2D, and 1.26 ± 0.40D for 4D. The polychromatic white DOFi were greater than the average monochromatic DOFi by 19%, 9% and 14% for 0D, 2D, and 4D of accommodative demand, respectively. CONCLUSION: The longitudinal chromatic aberration causes a dioptric shift of the monochromatic accommodation response. The study did not reveal this shift to depend on the accommodative demand or to have an effect on the DOFi.