Myopia Control Dose Delivered to Treated Eyes by a Dual-focus Myopia-control Contact Lens

Abstract

Purpose: This study examined the optical impact of a DF contact lens during near viewing in a sample of habitual DF lens wearing children.

Methods: Seventeen myopic children aged 14 to 18 years who had completed 3 or 6 years of treatment with a DF contact lens (MiSight 1 Day; CooperVision, Inc., San Ramon, CA) were recruited and fit bilaterally with the DF and a single-vision (Proclear 1 Day; CooperVision, Inc.) contact lens. Right eye wavefronts were measured using a pyramidal aberrometer (Osiris; CSO, Florence, Italy) while children accommodated binocularly to high-contrast letter stimuli at five target vergences. Wavefront error data were used to compute pupil maps of refractive state.

Results: During near viewing, children wearing single-vision lenses accommodated on average to achieve approximate focus in the pupil center but, because of combined accommodative lag and negative spherical aberration, experienced up to 2.00 D of hyperopic defocus in the pupil margins. With DF lenses, children accommodated similarly achieving approximate focus in the pupil center. When viewing three near distances (0.48, 0.31, and 0.23 m), the added +2.00 D within the DF lens treatment optics shifted the mean defocus from +0.75 to -1.00 D. The DF lens reduced the percentage of hyperopic defocus (≥+0.75 D) in the retinal image from 52 to 25% over these target distances, leading to an increase in myopic defocus (≤-0.50 D) from 17 to 42%.

Conclusions: The DF contact lens did not alter the accommodative behavior of children. The treatment optics introduced myopic defocus and decreased the amount of hyperopically defocused light in the retinal image.

FIGURE 1

Off-eye optical design of the single-vision and dual-focus lenses. Measured (ClearWave; Lumetrics, lumetrics.com) power maps for two sample contact lenses (single-vision (A) and dual-focus (B)) with labeled power −1.00 D from which zone-specific power distributions (C, D) were derived. Rings on the single-vision power map (A) mirror the zone boundaries observed in the dual-focus lens (B). Power distributions (C, D) characterize each of the four zones, quantified using bin widths of 0.25 D.

FIGURE 2

Data processing sequence with sample data starting at top left and finishing bottom right. (1) A sample anterior eye image collected from the aberrometer of an eye fit with a dual-focus CL, measured three times with the clinical Osiris aberrometer, which output three wavefront error maps. (2) Custom software implemented in MATLAB, calculated the local refractive state for each sample in the wavefront revealing the expected four-annular-zone structure of the MiSight CL. (3) Raw refractive state data were corrected for prism and lens centration errors, and (4) the measured zone geometry of this lens was used to locate zone boundaries in the maps. (5) In a few cases (3 of 17), it was observed that children would accommodate accurately on two of the three trials but fail to accommodate on the third. Mean data excluded the outlier data set. Also, data corrupted by blinks, lashes, and tear disruptions were excluded. (6) Refractive data from each zone (center zone and three surrounding rings, R1, R2, and R3) were isolated and (7) used to plot refractive state distributions for each individual zone. (8) Refractive state distributions were converted to defocus distributions by subtracting the target vergence (in diopters). CL = contact lens.

FIGURE 3

Methods used to classify the focused and defocused light in the retinal image. (A) Criteria for classifying myopically (red) and hyperopically (blue) defocused light and focused (black) light from the continuous distributions of measured retinal defocus. (B) Example ternary plot of the three dimensions of proportions of myopic, hyperopic, and focused light (red, blue, and black). Colored arrows show how proportions are determined for a given data point. Defocus = Refractive state (RS) – Target vergence (TV).

FIGURE 4

Full pupil defocus distributions from a sample eye. Defocus distributions (0.25 D bins) from the sample eye fit with the single-vision (top panel) and dual-focus (bottom panel) lenses for the full pupil. The measured refractive states were converted to defocus distributions (difference between the measured refractive state and the target vergence: defocus (diopters) = refractive state − target vergence) with positive values indicating hyperopically defocused light and negative for myopic defocus. Black dashed lines plot the position of the eye's retina where defocus is zero.

FIGURE 5

Zone-wise defocus distributions with single-vision and dual-focus lenses. Defocus distributions (0.25 D bins) for the same eye as Fig. 4, for four individual zones (two correction zones [center zone and R2] and two treatment zones [R1 and R3] for all five viewing distances). Defocus = Refractive state (RS) – Target vergence (TV).

FIGURE 6

Mean defocus (defocus = refractive state – target vergence) as a function of target vergence from all children. Mean defocus values (y axis) observed at each target vergence (x axis) were plotted for each zone (center zone, R1, R2, and R3) for eyes fit with the single-vision (A, C, E, G) or the dual-focus (B, D, F, H) contact lenses. Data for each of the 17 tested eyes were plotted as gray lines, and the mean of the 17 was plotted as a bold line and symbol. Error bars were ±1 SEM. SEM = standard error of the mean.

FIGURE 7

Zone-wise impact of dual-focus lens on the defocus of eyes compared with the single-vision control lens. Mean difference in defocus between the dual-focus and single-vision lens for four individual zones (two correction zones [center zone and R2] and two treatment zones [R1 and R3]) as a function of target vergence in diopters.

FIGURE 8

Ternary plots of focused and defocused light in the retinal image. The three proportions of focused and myopically and hyperopically defocused light forming the foveal images were extracted from the full pupil defocus distributions (Fig. 4) and plotted for each eye and each lens using three axes ternary plots. Data for eyes fit with the single-vision (A, C) and dual-focus (B, D) lenses for each viewing distance: 3.98 (filled circles), 0.98 (open circles), 0.48 (open squares), 0.31 (open diamonds), and 0.23 m (filled triangles) are plotted for the sample means (bold symbols and lines) and for each eye (low contrast gray symbols).