Optically Induced Peripheral Contrast Reduction Restores ON/OFF Pathway Balance in Myopic Eyes

Abstract

Purpose

The aim of this study was to investigate ON/OFF pathway responses and the impact of contrast reduction in myopes and emmetropes.

Design

This was a cross-sectional study.

Subjects

Thirty-eight young adult participants aged 20 to 29 years were included. Their spherical equivalent refraction ranged from +0.75 to –5.75 diopters (D).

Methods

All participants (20 myopes, 18 emmetropes) underwent multifocal electroretinogram recording after 90 minutes of exposure to monocular diffuse (contrast reduction) conditions. The 5 experimental conditions were assessed in random order on separate days for each participant: control (no diffuse), slight peripheral diffuse (0.8 Bangerter foil, 5 mm clear center), medium peripheral diffuse (MPD) (0.4 Bangerter foil, 9 mm clear center), MPD (0.4 Bangerter foil, 5 mm clear center), and medium full-field diffuse (0.4 Bangerter foil).

Main Outcome Measures

P1- and P2-wave amplitudes, as well as the P2/P1 amplitude ratio at varying retinal eccentricities were analyzed.

Results

Compared with those of emmetropic eyes, both P1- and P2-wave amplitudes were significantly lower in myopic eyes (P1-wave: 8.25 ± 1.42 vs 10.29 ± deg/deg², P < 0.05; P2-wave: 2.52 ± 0.79 vs 3.89 ± 1.57 nV/de g², P < 0.01). However, the decline in P2-wave amplitude (35%) was more pronounced than the reduction in P1-wave amplitude (20%), resulting in a decrease in the P2/P1 ratio (0.30 ± 0.07 vs 0.41 ± 0.19, P < 0.05). Compared with the control condition, all the peripheral diffuse conditions increased the P2-wave amplitude and significantly increased the P2/P1 ratio (0.38∼0.41 vs 0.30, all P < 0.05) in the entire analyzed field, whereas no change was observed in the full-field diffuse condition (P > 0.05). No significant differences between the slight and medium diffuse conditions were observed (P > 0.05).

Conclusions

Peripheral contrast reduction significantly strengthened OFF-pathway responses, contributing to the restoration of ON/OFF pathway balance in myopic eyes.

Financial Disclosure(s)

The author has no/the authors have no proprietary or commercial interest in any materials discussed in this article.

The contrast hypothesis of myopia has received increasing attention recently. Diffusion optics technology (DOT) lenses have been designed to generally reduce peripheral image contrast, with the hypothesis that this reduction may influence the effects of myopia control by modulating activity in both the ON and OFF pathways.¹ Findings from a randomized controlled trial (Control of Myopia Using Novel Spectacle Lens Designs, CYPRESS) indicated that DOT lenses are both safe and effective in reducing myopia progression.2, 3, 4 However, these findings may conflict with those of previous animal studies, which have shown that blurred retinal images produced by translucent diffusers (DOT-like), which primarily attenuate higher spatial frequencies and thereby alter the spatial-frequency distribution of retinal image contrast,⁵ can lead to form-deprivation myopia.⁶

Recent work has begun to elucidate how contrast and optical defocus modulate ON- and OFF-pathway responses and downstream retinal signaling.7, 8, 9, 10 Nevertheless, the mechanisms by which specific patterns of contrast reduction are integrated within these pathways to slow or promote refractive development remain incompletely understood, particularly in humans. Differences in refractive development (against or promoting myopia) due to blurred retinal images may suggest underlying mechanisms that guide how visual signals influence this process. Current optical characterization studies suggest that DOT lenses produce relatively mild, spatially selective image degradation compared with the dense diffusers typically used in animal form-deprivation paradigms.11, 12, 13, 14, 15 Such differences in optical design parameters, including the degree of contrast reduction, the size of the central clear optical zone, and the dimensions of the diffusion optical elements, may help determine whether contrast manipulation biases refractive development toward myopia inhibition or myopia induction.¹⁶

Given that contrast visual signals play a significant role in refractive development,¹⁷ and the ON and OFF pathways are critical for understanding these signals.⁹ The aims of this study were to investigate the impact of different contrast-reduction conditions on the central and peripheral retinal ON/OFF pathways, and to explore the possible working mechanism of contrast reduction.

Methods

Participants

Thirty-eight participants aged 20 to 29 years (mean age, 23.29 ± 1.52 years), recruited from among university students, participated in this study. The spherical equivalent refraction (SER) of the participants ranged from +0.75 to –5.75 diopters (D), with no cylindrical refraction >1.00 D and no anisometropia >1.00 D. Based on their refraction, the participants were classified as emmetropes or myopes (SER < –0.50 D). All had normal visual acuity of logarithm of the minimum angle of resolution 0.00 or better. Before the study, each participant underwent a comprehensive ophthalmic examination to ensure good ocular health and to assess refractive status. All participants were free of any ocular or systemic diseases and had no significant history of ocular trauma or surgery.

Ethics committee approval was obtained from the Eye Hospital of Wenzhou Medical University (2024-044-K-39-01). All procedures followed the principles of the Declaration of Helsinki, and participants provided written informed consent before participating.

Procedures

The experiment was conducted over 5 separate days for each participant, with each of the 5 different diffuse (contrast reduction) conditions tested on a different day in a random order. All experiments were taken at the same time each day (between 7 and 10 pm) for each participant to minimize the impact of diurnal fluctuations on visual electrophysiology responses.

At the beginning of each experiment, participants underwent mydriasis using 3 drops of a mixture of 0.5% tropicamide and 0.5% phenylephrine (QiuKang, Handan Kangye Pharmaceutical Co, Ltd), administered at 5-minute intervals. After a 15-minute rest after the last drop, participant watched a movie at a 5-meter distance for 90 min. During this period, they wore their best-corrected distance SER in both eyes, with the assigned diffuse lens additionally placed on their dominant eye (determined via the sighting dominance test¹⁸). Ambient illumination was maintained at approximately 170 lux throughout the viewing period. Finally, a long-duration multifocal electroretinogram (mfERG) recording of the intervention eye was conducted.

Test Lens Conditions

In this study, Bangerter occlusion foils (Ryser Optik AG, St) were pasted on the trial lenses to produce diffuse conditions. These foils are available in nominal densities (0.1–1.0) and reduce both visual acuity and contrast sensitivity in a density- and spatial-frequency–dependent, nonlinear manner.¹¹ All participants wore their best-corrected distance SER in both eyes, with the assigned diffuse lens placed on the dominant eye under each condition (Fig 1): (1) control: no diffuse; (2) slight peripheral diffuse (SPD) ∼5 mm: 0.8-density Bangerter foil with a 5 mm clear center aperture; (3) medium peripheral diffuse (MPD) ∼9 mm: 0.4-density foil with a 9 mm aperture; (4) MPD ∼5 mm: 0.4-density foil with a 5 mm aperture; and (5) medium full-field diffuse (MFD): 0.4-density foil fully covering.

Figure 1.

Description of the 5 diffuse visual conditions tested. A,Control condition: no diffuse. B, Slight peripheral diffuse condition ∼5 mm: SPD condition using a 0.8-density Bangerter foil with a 5 mm clear center aperture. C, Medium peripheral diffuse condition ∼9 mm: MPD condition using a 0.4-density Bangerter foil with a 9 mm clear center aperture. D, Medium peripheral diffuse condition ∼5 mm: MPD condition using a 0.4-density Bangerter foil with a 5 mm clear center aperture. E, Medium full-field diffuse condition: MFD condition using a 0.4-density Bangerter foil without a clear center aperture. MFD = medium full-field diffuse; MPD = medium peripheral diffuse; SPD = slight peripheral diffuse.

Stimulation and Electroretinogram Recordings

The intervention eye was selected for long-duration mfERG measurement using the RETI-port/scan21 system (Roland Consult). As an improvement over the conventional mfERG, long-duration mfERG employs temporally extended light and dark phases to enable functional separation of ON- and OFF-pathway responses. By isolating responses at stimulus onset and offset, this approach provides a localized assessment of postreceptoral retinal processing that cannot be achieved with brief-flash mfERG paradigms. Participants fixated on a red “X”-shaped target, with the other eye occluded. The pupil diameter was evaluated and maintained ≥7 mm before and after mfERG recording. A scaled 61-hexagon pattern, subtending 57° horizontally and 50° vertically, was displayed on a high-color liquid crystal display monitor (RadiForce MX242W; EIZO Corporation) at 29 cm. An electroretinogram (ERG)-jet corneal contact lens electrode was used for ERG recording, with a gold-cup electrode placed at the outer canthus as the reference electrode and another electrode on the central forehead as the ground electrode. The stimulus was presented at a 60 Hz frame rate, with room illuminance maintained at approximately 60 lux at the participant's eye level during recording.

Based on the work of Kondo et al^19,20 and the International Society for Clinical Electrophysiology of Vision²¹ for photopic ON–OFF ERG, we adapted the stimulation parameters to suit modern liquid crystal display–based devices²² (Figs S1–S3, available at www.ophthalmologyscience.org), allowing effective recording of multifocal ON (P1-wave) and OFF (P2-wave) responses. Each hexagonal element in the pattern alternated between 2 stimuli: stimulus A (7 consecutive dark frames after 9 consecutive white frames) and stimulus B (16 consecutive dark frames), as shown in Figure 2. Each base interval lasted approximately 266.7 ms (bright phase duration: 150 ms, dark phase duration: 116.7 ms). Focal responses were calculated as the difference between the average response to stimulus A and stimulus B. During the bright phase, the stimulus was set to 200 cd/m², whereas the dark phase and background luminance were maintained at 30 cd/m² (Fig 2). This modulation was managed using a binary m-sequence with 2⁹–1 steps, resulting in a total recording time of 9 min and 16 seconds. The mfERG signal was amplified using a digital-controlled amplifier (Roland Consult), with a sensitivity range of 10 μV/div to 2 mV/div, and bandpass filtered between 0.5 Hz and 300 Hz.

Figure 2.

Schematic diagram for grouping the mfERG responses and the waveform characteristics of a long-duration mfERG. A, Responses were pooled into 5 concentric rings based on eccentricity (visual angle), ranging from ring 1 (1.99°) to ring 5 (28.51°) for analysis. B, The stimulus array comprises 61 hexagonal elements, with luminance levels set to 200 cd/m² for the bright phase and 30 cd/m² for the dark phase. The peripheral luminance of the display screen was maintained at 30 cd/m². C, Stimulus configuration for the long-duration mfERG. Each hexagon alternated between Stimulus A (7 consecutive dark frames after 9 consecutive white frames) and Stimulus B (16 consecutive dark frames), controlled by a binary m-sequence. Focal responses were computed as the difference between the average response to stimulus A and stimulus B. The bottom right section of the figure depicts a typical ERG waveform with ON (P1-wave) and OFF (P2-wave) responses of the long-duration mfERG. ERG = electroretinogram; mfERG = multifocal electroretinogram.

Data Analysis

Ring analysis was conducted to examine physiological changes in ON (P1-wave) and OFF (P2-wave) responses at different retinal eccentricities. To further explore the relationship between the ON and OFF pathways, the ratio of P2-wave to P1-wave amplitude (P2/P1 ratio) was calculated and plotted.

Data are presented as the mean ± standard deviation. Statistical analysis was performed using IBM SPSS Statistics software, version 27 (SPSS, Inc). Independent-sample t tests were used to compare the condition between the myopic and emmetropic groups. To evaluate differences across the 5 diffuse lens conditions, a 1-way repeated-measures analysis of variance was conducted for each region in myopes and emmetropes, followed by a post hoc Bonferroni correction. A P value <0.05 was considered statistically significant.

Results

Electroretinograms were recorded from the dominant eye of 18 emmetropic and 20 myopic young adults (Table 1). One emmetropic participant completed only the control condition test; therefore, data from 17 emmetropic participants were used in the analysis of the different diffuse conditions.

Table 1.

Demographic and Ocular Characteristics of the Participants

	Emmetropes (n = 18∗)	Myopes (n = 20)	P Value
Age, y	23.28 ± 1.93	23.30 ± 1.08	0.90
Sex
Male	5	10	0.16
Female	13	10
SER, dominant eye, D	–0.12 ± 0.31	–3.35 ± 1.26	<0.001
Axial length, mm	23.30 ± 0.70	25.20 ± 1.10	<0.001

D = diopter; SER = spherical equivalent refraction.

Data are presented as mean ± standard deviation.

^∗One emmetropic participant was tested only under the control condition before discontinuation.

ON and OFF Responses at Different Retinal Eccentricities

In the control condition, both emmetropic and myopic eyes consistently showed a P1-wave amplitude that exceeded the P2-wave amplitude (emmetropic eyes: 10.29 ± 3.23 vs 3.89 ± 1.57 nV/deg²; myopic eyes: 8.25 ± 1.42 vs 2.52 ± 0.79; Fig 3A). Moreover, both P1- and P2-wave amplitudes gradually decreased with increasing retinal eccentricity (Fig 3C, D).

Figure 3.

Physiological differences in ON (P1-wave) and OFF (P2-wave) responses across the 5-ring field and at different retinal eccentricities (rings) in the control condition, consisting of myopes (n = 20) and emmetropes (n = 18). A, The P1- and P2-wave amplitudes in the entire analyzed field; B, P2/P1 ratio in the entire analyzed field; C, P1-wave amplitude at different retinal eccentricities; D, P2 amplitude at different retinal eccentricities; E, P2/P1 ratio at different retinal eccentricities. Data are presented as mean ± SD. Statistical significance is indicated for data compared between emmetropes and myopes: ∗P < 0.05, ∗∗P < 0.01, ∗∗∗P < 0.001. SD = standard deviation.

Compared with emmetropic eyes, myopic eyes presented significantly lower P1- and P2-wave amplitudes in the entire analyzed field ((P1-wave: 8.25 ± 1.42 vs 10.29 ± 3.23 nV/deg², P < 0.05; P2-wave: 2.52 ± 0.79 vs 3.89 ± 1.57 nV/deg², P < 0.01; Fig 3A) and across all examined local regions (P1-wave: 64.06 ∼ 5.43 vs 77.55 ∼ 7.01 nV/deg², all P < 0.05, Fig 3C; P2-wave: 30.64 ∼ 2.03 vs 52.07 ∼ 3.35 nV/deg², all P < 0.05, Fig 3D). However, the reduction in P2-wave amplitude was more pronounced (P2-wave vs P1-wave, ring 1: 41.15% vs 17.40%; ring 2: 37.00% vs 20.22%; ring 3: 46.59% vs 19.57%; ring 4: 39.01% vs 22.37%; Ring 5: 39.20% vs 22.56%), resulting in a consistently lower P2/P1 ratio in myopic eyes (0.26 ∼ 0.48 vs 0.40 ∼ 0.65 in emmetropic eyes, all P < 0.05; Fig 3E).

ON and OFF Responses to Contrast Reduction in Myopes

No significant differences in P1-wave amplitude were observed among the intervention conditions in the entire analyzed field (F = 0.342, P = 0.849), whereas significant differences were observed in P2-wave amplitude (F = 3.474, P = 0.012) and the P2/P1 ratio (F = 4.158, P = 0.004). Post hoc analysis revealed that both MPD conditions (9 mm and 5 mm clear center apertures) significantly increased the P2-wave amplitude (9 mm: 3.16 ± 1.02 nV/deg²; 5 mm: 3.07 ± 0.88 nV/deg²; respectively, vs control, 2.52 ± 0.79 nV/deg²; both P < 0.05, Fig 4A) and in the P2/P1 ratio (9 mm: 0.41 ± 0.17; 5 mm: 0.38 ± 0.13, respectively, vs control, 0.30 ± 0.07; both P < 0.05, Fig 4A). Similarly, the SPD condition (∼5 mm) significantly increased the P2/P1 ratio (0.38 ± 0.10 vs 0.30 ± 0.07, P < 0.01). In contrast, the MFD condition did not significantly affect any parameter in the entire analyzed field (P > 0.05, Fig 4A).

Figure 4.

The long-duration mfERG ON and OFF responses to different lens conditions at varying retinal eccentricities in myopes (n = 20). Bar charts illustrating the P1-wave amplitude, P2-wave amplitude, and P2/P1 ratio under various lens conditions, are presented for the entire analyzed field (A), ring 1 (B), ring 2 (C), ring 3 (D), ring 4 (E), and ring 5 (F). Data are presented as mean ± SD. Statistical significance is indicated as follows: ∗P < 0.05, ∗∗P < 0.01, vs control condition; #P < 0.05, ##P < 0.01 vs MPD condition ∼9 mm; † P < 0.05 vs MPD condition ∼5 mm. MPD = medium peripheral diffuse; MFD = medium full-field diffuse; mfERG = multifocal electroretinogram; SD = standard deviation; SPD = slight peripheral diffuse.

Eccentricity-specific analysis showed significant differences among intervention conditions in P2-wave amplitude (ring 1: F = 3.812, P = 0.007; ring 2: F = 4.35, P = 0.003; ring 3: F = 5.66, P < 0.001; ring 4: F = 8.003, P < 0.001; ring 5: F = 3.044, P = 0.022) and the P2/P1 ratio (ring 1: F = 2.131, P = 0.085; ring 2: F = 4.535, P = 0.002; ring 3: F = 6.993, P < 0.001; ring 4: F = 5.296, P < 0.001; ring 5: F = 2.336, P = 0.063) in most rings.

Specifically, the MPD condition (∼9 mm) significantly increased both P2-wave amplitude (ring 2-5: 4.33∼13.90 vs 3.19 ∼ 9.38 nV/deg², all P < 0.05) and P2/P1 ratio (ring 2–4: 0.46 ∼ 0.53 vs 0.26 ∼ 0.38, all P < 0.05) in most rings compared with the control condition, particularly rings 2–4 (Fig 4C–E). Under the MPD condition (∼5 mm), the P2-wave amplitude increased significantly in ring 3 (6.69 ± 2.70 vs 4.30 ± 1.66 nV/deg², P < 0.05, Fig 4D) and ring 4 (4.24 ± 1.30 vs 3.19 ± 1.17 nV/deg², P < 0.01, Fig 4E), while the P2/P1 ratio was significantly elevated only in ring 3 (0.44 ± 0.17 vs 0.26 ± 0.11, P < 0.01, Fig 4C). Under the SPD condition, P2-wave amplitude increased significantly only in ring 4 (4.21 ± 1.38 vs 3.19 ± 1.17 nV/deg², P < 0.05; Fig 4E), while the P2/P1 ratio remained unchanged across all regions (all P > 0.05, Fig 4B–F). The MFD condition again showed no significant differences from the control in any retinal subregion (all P > 0.05, Fig 4B–F). Finally, no significant differences were found between SPD and MPD (∼5 mm), or between the 2 MPD aperture sizes (5 mm vs 9 mm) in any analyzed region (Fig 4).

ON and OFF Responses to Contrast Reduction in Emmetropes

In emmetropic eyes, no significant differences in the P1-wave amplitude (entire analyzed field: P = 0.3; ring 1: P = 0.479; ring 2: P = 0.587; ring 3: P = 0.227; ring 4: P = 0.466; ring 5: P = 0.215), P2-wave amplitude (entire analyzed field: P = 0.759; ring 1: P = 0.147; ring 2: P = 0.540; ring 3: P = 0.743; ring 4: P = 0.433; ring 5: P = 0.141), or P2/P1 ratio (entire analyzed field: P = 0.716; ring 1: P = 0.656; ring 2: P = 0.925; ring 3: P = 0.974; ring 4: P = 0.278; ring 5: P = 0.774) were observed across the 5 diffuse lens conditions. Specifically, post hoc analysis revealed that none of the pairwise comparisons among the 5 lens conditions resulted in significant changes in these parameters across any retinal region (all P > 0.05; Fig 5).

Figure 5.

The long-duration mfERG ON and OFF responses to different lens conditions at varying retinal eccentricities in emmetropes (n = 17). Bar charts illustrating the P1-wave amplitude, P2-wave amplitude, and P2/P1 ratio under various lens conditions, are presented for the entire analyzed field (A), ring 1 (B), ring 2 (C), ring 3 (D), ring 4 (E), and ring 5 (F). Data are presented as mean ± SD. MFD = medium full-field diffuse; mfERG = multifocal electroretinogram; MPD = medium peripheral diffuse; SD = standard deviation; SPD = slight peripheral diffuse.

Restoration of ON/OFF Balance in Myopic Eyes After Contrast Reduction

The P2/P1 ratio in the entire analyzed field of myopic eyes increased under both MPD and SPD conditions after contrast reduction, reaching levels comparable to those in emmetropic control (MPD ∼9 mm: 0.41 ± 0.17 vs 0.41 ± 0.19, P = 0.98; MPD ∼5 mm: 0.38 ± 0.13 vs 0.41 ± 0.19, P = 0.58; SPD ∼5 mm: 0.38 ± 0.10 vs 0.41 ± 0.19, P = 0.57; Table 2). Eccentricity-specific analysis revealed that this increase in the P2/P1 ratio was observed at each ring, reaching levels comparable to those of emmetropic controls across the entire field (all P > 0.05, Fig 6C–E).

Table 2.

Long-Duration mfERG P1-Wave Amplitude, P2-Wave Amplitude, and P2/P1 Ratio at Different Retinal Eccentricities after Lens Wear in Emmetropic and Myopic Eyes under 5 Conditions: Control, SPD ∼5 mm, MPD ∼9 mm, MPD ∼5 mm, and MFD Conditions

Region	Component/Lens Conditions	Emmetropes (n = 18∗)					Myopes (n = 20)
		Control Condition	SPD Condition ∼5 mm	MPD Condition ∼9 mm	MPD Condition ∼5 mm	MFD Condition	Control Condition	SPD Condition ∼5 mm	MPD Condition ∼9 mm	MPD Condition ∼5 mm	MFD Condition
Entire analyzed field	P1-wave, nV/deg2	10.29 ± 3.23	10.49 ± 2.51	9.82 ± 3.2	10.90 ± 3.28	10.61 ± 3.57	8.25 ± 1.42	8.4 ± 1.98	8.21 ± 2.30	8.66 ± 2.52	8.32 ± 1.89
	P2-wave, nV/deg2	3.89 ± 1.57	3.94 ± 1.52	3.61 ± 1.17	3.82 ± 1.25	3.73 ± 1.44	2.52 ± 0.79	3.13 ± 0.87	3.16 ± 1.02	3.07 ± 0.88	2.75 ± 1.13
	P2/P1 ratio	0.41 ± 0.19	0.38 ± 0.15	0.40 ± 0.15	0.37 ± 0.15	0.37 ± 0.14	0.30 ± 0.07	0.38 ± 0.10	0.41 ± 0.17	0.38 ± 0.13	0.34 ± 0.13
Ring 1	P1-wave, nV/deg2	77.55 ± 21.15	80.31 ± 55.66	65.65 ± 25.56	71.78 ± 22.81	67.86 ± 26.35	64.06 ± 13.84	64.66 ± 20.62	70.16 ± 23.46	62.27 ± 19.84	51.33 ± 14.83
	P2-wave, nV/deg2	52.07 ± 24.86	45.21 ± 25.64	41.16 ± 12.31	45.80 ± 18.85	37.89 ± 16.38	30.64 ± 10.34	36.57 ± 14.74	43.04 ± 19.92	39.4 ± 18.61	26.44 ± 11.72
	P2/P1 ratio	0.65 ± 0.22	0.63 ± 0.26	0.70 ± 0.30	0.68 ± 0.30	0.58 ± 0.19	0.48 ± 0.13	0.57 ± 0.14	0.63 ± 0.26	0.64 ± 0.25	0.53 ± 0.26
Ring 2	P1-wave, nV/deg2	32.43 ± 9.84	31.5 ± 6.90	30.53 ± 9.13	30.56 ± 8.55	30.21 ± 8.93	25.87 ± 6.72	29.27 ± 10.12	27.61 ± 8.10	27.42 ± 7.95	26.95 ± 4.96
	P2-wave, nV/deg2	14.90 ± 5.51	12.91 ± 4.77	12.77 ± 6.08	14.21 ± 4.88	12.71 ± 6.38	9.38 ± 2.64	12.2 ± 5.65	13.9 ± 4.25	12.18 ± 5.72	9.02 ± 3.85
	P2/P1 ratio	0.48 ± 0.16	0.43 ± 0.17	0.45 ± 0.25	0.48 ± 0.16	0.46 ± 0.25	0.38 ± 0.14	0.43 ± 0.14	0.53 ± 0.22	0.49 ± 0.26	0.33 ± 0.12
Ring 3	P1-wave, nV/deg2	20.71 ± 6.63	21.57 ± 5.18	18.95 ± 4.58	19.64 ± 6.05	19.66 ± 6.56	16.66 ± 2.83	16.75 ± 4.43	16.57 ± 4.67	15.80 ± 4.06	16.85 ± 3.02
	P2-wave, nV/deg2	8.06 ± 2.54	7.87 ± 2.37	7.27 ± 2.66	7.45 ± 3.32	7.35 ± 3.61	4.3 ± 1.66	6.36 ± 2.47	7.17 ± 3.23	6.69 ± 2.70	5.00 ± 1.91
	P2/P1 ratio	0.40 ± 0.11	0.38 ± 0.13	0.40 ± 0.14	0.39 ± 0.16	0.41 ± 0.20	0.26 ± 0.11	0.4 ± 0.17	0.46 ± 0.21	0.44 ± 0.17	0.30 ± 0.12
Ring 4	P1-wave, nV/deg2	11.42 ± 4.25	10.71 ± 3.07	11.54 ± 3.12	12.01 ± 3.68	11.99 ± 3.79	8.86 ± 1.88	9.54 ± 2.65	9.28 ± 3.10	9.87 ± 3.14	8.69 ± 2.19
	P2-wave, nV/deg2	5.24 ± 2.08	4.59 ± 1.34	4.72 ± 1.21	4.93 ± 1.78	5.19 ± 1.92	3.19 ± 1.17	4.21 ± 1.38	4.33 ± 1.80	4.24 ± 1.30	2.88 ± 1.13
	P2/P1 ratio	0.52 ± 0.28	0.45 ± 0.13	0.43 ± 0.14	0.43 ± 0.16	0.45 ± 0.16	0.36 ± 0.12	0.45 ± 0.13	0.50 ± 0.20	0.47 ± 0.20	0.34 ± 0.11
Ring 5	P1-wave, nV/deg2	7.01 ± 2.31	7.27 ± 1.89	6.69 ± 1.95	7.72 ± 2.48	7.34 ± 2.80	5.43 ± 1.07	5.52 ± 1.57	5.67 ± 1.69	5.80 ± 1.88	5.51 ± 1.77
	P2-wave, nV/deg2	3.35 ± 1.39	3.64 ± 1.15	3.15 ± 0.91	3.82 ± 0.99	3.27 ± 1.03	2.03 ± 0.63	2.57 ± 1.06	2.77 ± 1.00	2.64 ± 1.05	2.51 ± 0.90
	P2/P1 ratio	0.50 ± 0.21	0.52 ± 0.19	0.49 ± 0.14	0.57 ± 0.33	0.55 ± 0.41	0.38 ± 0.08	0.5 ± 0.25	0.51 ± 0.17	0.50 ± 0.22	0.49 ± 0.21

MFD = medium full-field diffuse; mfERG = multifocal electroretinogram; MPD = medium peripheral diffuse; SPD = slight peripheral diffuse.

Data are presented as mean ± SD.

^∗One emmetropic participant was tested only under the control condition before discontinuation.

Figure 6.

Physiological differences in the ratio of OFF (P2-wave) to ON (P1-wave) responses at different retinal eccentricities (rings) between myopes (n = 20) and emmetropes (n = 18). A, Differences in the P2/P1 ratio between emmetropic and myopic controls; (B) differences in the P2/P1 ratio between emmetropic control and myopic MFD; (C) differences in the P2/P1 ratio between emmetropic control and myopic SPD ∼5 mm; (D) differences in the P2/P1 ratio between emmetropic control and myopic MPD ∼5 mm; (E) differences in the P2/P1 ratio between emmetropic control and myopic MPD ∼9 mm. Data are presented as mean ± SD. Statistical significance is indicated as follows: ∗P < 0.05, ∗∗P < 0.01, ∗∗∗P < 0.001, vs emmetropic control. MFD = medium full-field diffuse; MPD = medium peripheral diffuse; SD = standard deviation; SPD = slight peripheral diffuse.

Discussion

This study investigated ON and OFF retinal responses in young adult human eyes that were exposed to periods of monocular contrast reduction. Both ON and OFF responses were reduced in myopic participants compared to emmetropes, with significantly greater reductions observed in OFF responses across all examined regions, thereby exacerbating the ON/OFF imbalance (Fig 3). Notably, under peripheral contrast-reduction conditions, OFF-pathway responses in myopic eyes were significantly enhanced relative to the no-diffuse control condition (Fig 4), thereby contributing to the restoration of ON/OFF pathway balance in myopic eyes (Fig 6).

Human vision processes light and dark stimuli through distinct ON and OFF neuronal pathways. Their interaction underlies contrast processing and has been implicated in myopia.¹⁷ However, the specific contributions of these pathways to refractive development remain controversial. Several studies have highlighted the critical role of ON pathway deficits in myopia development,^9,23 whereas pharmacologic manipulations in animal models suggest the opposite directionality: suppressing ON signaling constrains eye growth and can induce hyperopia.²⁴ Similarly, selective OFF activation in humans produces choroidal thinning,²⁵ a change associated with myopic shift, but genetic data indicate a protective role of OFF signaling—reduced OFF pathway activity is associated with the myopia risk allele at the GJD2 locus.^26,27 In chicks, inhibiting the OFF pathway with D-α-aminoadipic acid disrupts refractive compensation for positive lens defocus,²⁸ and in guinea pigs, Wang et al²⁹ observed that stimulating either ON or OFF pathways suppressed myopia. Taken together, these seemingly contradictory results underscore a context-dependent, dual contribution of ON and OFF signaling to refractive development.

Building on this, changes in retinal function specific to myopia itself have increasingly become a key research focus in recent years. A previous study revealed reduced ON and OFF response in myopic human eyes;³⁰ however, the extent of reduction between these 2 pathways was not fully explored. Anatomically, the retina devotes more resources to OFF pathways, characterized by higher synaptic densities and greater neuron numbers,³¹ reflecting structural complexity that may render it more vulnerable to dysfunction. Moreover, the study in mice has also shown that OFF retinal ganglion cells are more susceptible to injury.³² This finding may explain the greater OFF-pathway vulnerability in myopic eyes when both ON and OFF signaling were affected in myopic eyes in this study, which is consistent with findings from the myopic mice study (Mazade R, et al. IOVS 2022; 63: ARVO E-Abstract 4580–F0442) and other ocular pathologies.^33,34 Stoimenova³⁵ also demonstrated that myopia reduced contrast sensitivity, with a more pronounced increase in negative contrast thresholds than in positive contrast thresholds, again suggesting preferential impairment of OFF-pathway function, which is consistent with our results.

Interestingly, peripheral contrast reduction boosted OFF-pathway activity in myopic eyes (Fig 4). This selective enhancement may result from an increase in negative contrast (dark) information after contrast reduction. However, boosted OFF-pathway activity in myopic eyes did not reach the levels observed in emmetropic controls (Table 2), but it helped rebalance ON/OFF signaling and restored the response ratio to within the emmetropic range (Fig 6).

In individuals with complete congenital stationary night blindness, which is characterized by ON pathway dysfunction, high myopia is common. In contrast, incomplete congenital stationary night blindness, which affects both ON- and OFF-pathway signals, is linked to milder myopia.³⁶ Findings from Alonso et al⁷ suggest that the “stop signal” for eye growth may correspond to the balanced or optimal activation of both ON and OFF retinal pathways. Consistent with this, our results suggest that the myopic retina exhibits impairments in both ON and OFF pathways, with more pronounced deficits in the OFF pathway, resulting in ON/OFF imbalance and a relatively ON-dominated response. These observations suggest that myopia may stem from imbalances between the ON and OFF pathway rather than a profound loss of either pathway.²⁷ Within the established frameworks of divisive normalization and contrast gain control, changes in stimulus contrast do not simply scale neural response amplitudes, but dynamically redistribute response gain across retinal pathways.37, 38, 39 Under reduced-contrast conditions, contrast gain control adjusts both response slope and dynamic range, thereby reweighting ON- and OFF-pathway contributions to maintain stable retinal output. Because OFF pathways are preferentially driven by luminance decrements and dark edges, this gain reallocation can result in a compensatory enhancement of OFF-pathway responses when overall contrast is reduced. Such a mechanism provides a physiologically grounded explanation for the observed OFF-pathway enhancement under contrast-reduction conditions in myopic eyes. Accordingly, the efficacy of DOT in myopia control may be mediated by the restoration of ON/OFF pathway balance in the retina.

In addition to contrast manipulation, optical defocus induced by positive or negative lenses is known to differentially modulate retinal signaling and eye growth.⁶ Experimental and human electrophysiological studies have shown that myopic and hyperopic defocus can alter the relative activation of ON and OFF pathways.⁷ From this perspective, contrast-based and defocus-based optical interventions may not represent fundamentally distinct mechanisms.⁴⁰ When retinal image contrast is artificially reduced by myopia-control optics, the resulting spatial-frequency–dependent blur may be interpreted by the retina as a defocus-related signal, resembling either hyperopic or myopic defocus. Accordingly, contrast manipulations may influence eye growth not only by modulating ON/OFF pathway activity, but also by altering the distribution of spatial-frequency information available to the retina, thereby biasing defocus-related retinal signaling that guides ocular growth.

In myopic eyes, the size of the central clear optical zone (∼5 mm, 5.95°; ∼ 9 mm, 10.62°, eccentricity) plays a critical role in modulating retinal responses. Central contrast reduction under the MFD condition suppressed peripheral OFF-pathway responses, as evidenced by the lack of significant improvements across the examined regions, unlike the enhancement observed under the peripheral-only diffuse conditions (Fig 4). This finding may help reconcile previous conflicting animal study,⁴¹ in which strong full-field diffusers have been shown to induce deprivation myopia. In this study, the MPD condition ∼9 mm notably increased the P2-wave amplitude (Fig 4A) and mitigated OFF-pathway deficits in myopic eyes, even within the clear center where contrast was not reduced, especially in ring 2 (13.9 ± 4.25 vs 9.38 ± 2.64 nV/deg², P < 0.01, Fig 4C). These findings could support the idea that peripheral visual signals may play a dominant role in central refractive development.⁴²

Ring analysis revealed that the MPD condition ∼5 mm may result in more limited retinal benefits, with OFF-response enhancement confined to a smaller retinal area (rings 3–4, Fig 4D–E) than the ∼9 mm condition (rings 2–5, Fig 4C–F), despite the lack of significant differences between the 2 peripheral diffuse conditions across all examined regions. Consequently, retinal sensitivity and response to regionally reduced-contrast signals may vary with eccentricity due to eccentricity-dependent photoreceptor density and receptive-field organization, which become progressively larger in the periphery. The boundary of this differential effect may lie between the retinal shadows projected by the ∼5 mm and ∼9 mm clear center aperture (5.95°–10.62°, eccentricity), as indicated by the subtle response differences observed across the 3 medium diffuse conditions (∼9 mm most effective, ∼5 mm limited, ∼0 mm suppressive). The retinal zone between 6° and 12° eccentricity is thought to be most sensitive to blur signals.⁴³ This is closely aligned with the boundary we hypothesized for the central and peripheral retinal response differences. Although the 2 concepts are not identical, this finding suggests the special role of the near-peripheral retina in visual development. Clinically, these results imply that overly small central clear optical zones may not provide additional benefit in children, highlighting the likelihood of an optimal zone size. Determining this optimal range will require further targeted investigation.

Both slight and medium peripheral contrast reductions increased the P2/P1 ratio compared with control (Fig 4A), although no significant differences in retinal response enhancement were observed between them in this study. However, compared with the MPD condition, the SPD condition resulted in more limited retinal benefits, with only ring 4 showing a significant increase in P2-wave amplitude (Fig 4E). The CYPRESS trial has discussed the possibility of a dose–response effect across DOT lens designs;^2,4 however, in the 3-year follow-up, the lens with stronger contrast reduction (test 2) showed numerically lower myopia-control efficacy than the milder design (test 1), and the authors noted that this pattern should be interpreted cautiously given substantial attrition and reduced effective sample size.⁴ One practical explanation is that stronger contrast manipulation may compromise wear tolerance and adherence in children, thereby reducing the delivered “effective dose” of the intervention and limiting observable efficacy in long-term trials. In our experiment, the MPD condition appeared more effective than the SPD condition (although not statistically significant), highlighting that the relationship between contrast manipulation strength and treatment efficacy may not be monotonic and may depend on both optical design and patient compliance. Future studies spanning a broader range of contrast attenuation (e.g., including stronger diffusers such as lower-grade Bangerter foils) and explicitly accounting for adherence may help determine whether a true dose–response relationship and a plateau effect exists, while identifying an optimal balance between contrast modulation and tolerability for children's use.

This study has also revealed intriguing differences in the response to contrast reduction between myopes and emmetropes. In emmetropes, contrast reduction did not significantly affect ON- or OFF-pathway responses. In contrast, emmetropes exhibit reduced sensitivity to visual input, which is consistent with a previous report that prolonged near work induces less axial elongation in emmetropic eyes than in myopic eyes.⁴⁴ Long-term observation may be required to further explore the effects of peripheral contrast reduction on myopic and nonmyopic eyes.

One limitation of this study is that the findings are based on adults, and it remains unclear whether similar changes occur in children. Further research is needed to confirm the role of the ON/OFF pathways in myopia onset and progression. Additionally, the observed changes appear to reflect cone-mediated rather than rod-mediated signaling. While the peripheral retina, where rods vastly outnumber cones,⁴⁵ plays a critical role in ocular growth regulation, the potential involvement of scotopic signaling in myopia cannot be excluded. However, as rod bipolar cells are exclusively ON-type, their involvement in the OFF pathway requires reliance on rod–cone interaction mechanisms, with the cone system initiating downstream ON/OFF signaling pathways.⁴⁶

Conclusions

The central and peripheral retina exhibit distinct responses to contrast reduction, with peripheral contrast reduction strengthening OFF-pathway responses and restoring ON/OFF balance. These findings support the hypothesis that modulations in light-adapted cone system signaling, particularly those affecting ON/OFF pathway balance, may contribute to myopia development.

Manuscript no. XOPS-D-25-00779.