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Peer-Review Record

Does Stimulation of Plantar Mechanoreceptors Alter Visual Spatial Localization?

J. Funct. Morphol. Kinesiol. 2026, 11(1), 74; https://doi.org/10.3390/jfmk11010074

by Philippe Villeneuve¹

, Frédéric Viseux^2,3,4

, Rodolfo Parreira⁵

and Maria Pia Bucci^1,6,*

Reviewer 1:

Masahiro Furukawa

Reviewer 2: Anonymous

Reviewer 3:

Dimitris Mandalidis

J. Funct. Morphol. Kinesiol. 2026, 11(1), 74; https://doi.org/10.3390/jfmk11010074

Submission received: 27 October 2025 / Revised: 5 February 2026 / Accepted: 6 February 2026 / Published: 12 February 2026

(This article belongs to the Special Issue Insights into the Assessment Strategies and Non-Pharmacological Management of Musculoskeletal Dysfunctions Linked to Chronic Pain Condition)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study demonstrates that foot sole stimulation contributes to vertical heterophoria (VH) in postural control. Therefore, three conditions were established for foot sole stimulation conditioning, utilizing hardness and surface texture. The academic contribution of this study lies in proposing a method to detect vertical heterophoria (VH) with high precision (less than 1/2 diopter) in under one minute. Furthermore, to clarify the correlation between foot stimulation and VH, the proposed method compares the three foot stimulation conditions.

While the effectiveness of the proposed method is claimed, it is judged not to have reached the standard for publication for the following reasons.

(1) The purpose of this study is unclear.
It is ambiguous whether the primary objective is to propose a method capable of measuring VH with high precision below 1/2 diopter, or to measure the correlation between foot sole stimulation and VH. Whether the validity of the calibration measurement method can be demonstrated from Figure 4 remains unclear for the reasons stated in the next section. Furthermore, if the goal is to clarify the correlation between plantar stimulation and VH, the design intent and validity of the pins used for plantar stimulation require justification. However, only hardness and external dimensions are provided, lacking any design rationale. The only mention is the expectation of effectiveness stated in lines 34 and 35.

(2) The statistical analysis methods are inadequate. The experimental paradigm involves classifying 95 participants into one of orthophoria, hypophoria, or hyperphoria using the proposed method under three plantar conditioning conditions. Since participants are necessarily classified into one category under each plantar stimulation condition, these classifications are not independent, effectively reducing the degrees of freedom to two. However, as stated in line 242, the authors conducted hypothesis testing under three independent conditions. Please review the validity of the testing method.
Furthermore, two different tests are performed on the same measurement data, raising concerns about statistical false detection (Type I error). Specifically, a Friedman test is performed on the foot stimulation condition, and a Kruskal-Wallis test is performed on the categorized groups (lines 234-248).

(3) There are points where the findings obtained diverge from the trends in prior research. Lines 102-139 provide a detailed explanation of the postural reflex system; however, as this has no direct relevance to the results obtained in this study, it appears to constitute excessive discussion. The experimental findings of this study lie in the high precision of measurement, achieving accuracy below 1/2 diopter, and in the fact that foot sole stimulation conditioning altered the distribution of orthophoria, hypophoria, and hyperphoria among the experimental participant groups. However, the prior research cited in lines 102-139 is not relevant to the foot stimulation design, and the experimental protocol itself has very little bearing on the discussion in lines 102-139. As mentioned earlier, revision of lines 102-139 is necessary to provide an academic justification for the foot stimulation design.

The graph in Figure 4 on p.8 appears to represent the value described as “the phoria” in line 250, but the definition of “the phoria (phoria value)” is not provided. The calculation method for the phoria value must be explicitly stated. It likely uses the ratio of participants across all subjects, but this could not be interpreted. Furthermore, it is unclear whether the sample values used for testing represent percentages or actual numbers of participants. While Figure 4 suggests the percentage values might be treated as sample values, this should be explicitly stated.

Additional comments:

The arrangement of the figures on p.7 Figure.3 and the order of the graphs on p.8 Figure.4 should be changed to {Baseline, Pins, Form} to aid reader comprehension.

P.7 Figure.3 contains a spelling error in the word “Form” (should be “Foam”), marked with a red line for proofreading. The figure should be corrected.
Additionally, the enclosed numbers [1][2] should be removed.

Author Response

Replies and changes in the text from Reviewer 1 are in red and Reviewer 2 are in blue

Reviewer #1

The purpose of this study is unclear.
It is ambiguous whether the primary objective is to propose a method capable of measuring VH with high precision below 1/2 diopter, or to measure the correlation between foot sole stimulation and VH. Whether the validity of the calibration measurement method can be demonstrated from Figure 4 remains unclear for the reasons stated in the next section. Furthermore, if the goal is to clarify the correlation between plantar stimulation and VH, the design intent and validity of the pins used for plantar stimulation require justification. However, only hardness and external dimensions are provided, lacking any design rationale. The only mention is the expectation of effectiveness stated in lines 34 and 35.

R: Thank you for this important observation. We agree that the aims required clarification. In the revised version, we have restructured the final part of the Introduction to clearly state that the main objective of the study was to investigate how subtle stimulation of plantar mechanoreceptors affects VH in healthy adults, using a new measurement device designed to detect small VH values (<1/2 prism diopter) quickly and precisely. Additionally, we have expanded the rationale for the pin design, explaining that their geometry was intended to selectively activate superficial plantar mechanoreceptors (Merkel cells, Meissner corpuscles) without discomfort, whereas the foam condition reduces afferent feedback. This better defines the physiological basis for the chosen materials and clarifies the study’s focus.

Furthermore, two different tests are performed on the same measurement data, raising concerns about statistical false detection (Type I error). Specifically, a Friedman test is performed on the foot stimulation condition, and a Kruskal-Wallis test is performed on the categorized groups (lines 234-248).

R: We thank the reviewer for this insightful statistical observation. We agree that the data represent repeated measurements within the same participants, and the assumption of independence among the three plantar conditions was not fully appropriate. In the revised manuscript, we have updated the Statistical Analysis section to clarify that a Friedman test was used to compare the three related conditions (baseline, pins, foam), with Bonferroni-corrected Wilcoxon signed-rank tests for pairwise comparisons. For categorical comparisons of vertical heterophoria classifications (orthophoria, hyperphoria, hypophoria), Cochran's Q test was used, which properly accounts for repeated binary/categorical outcomes. These modifications ensure that statistical inference respects the within-subject design and that Type I error rates are properly controlled.

R: We thank the reviewer for this constructive observation. We agree that the section between lines 102–139 contained excessive detail on general postural reflexes that were not directly linked to the experimental protocol. In the revised manuscript, this section has been rewritten to provide a clearer justification for the design of the foot stimulation conditions.

(4) The graph in Figure 4 on p.8 appears to represent the value described as “the phoria” in line 250, but the definition of “the phoria (phoria value)” is not provided. The calculation method for the phoria value must be explicitly stated. It likely uses the ratio of participants across all subjects, but this could not be interpreted. Furthermore, it is unclear whether the sample values used for testing represent percentages or actual numbers of participants. While Figure 4 suggests the percentage values might be treated as sample values, this should be explicitly stated.

R: Thank you for this observation. The definition and calculation of the “phoria value” have now been clarified in the Methods section (Statistical Analysis) and in the Figure 4 legend.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors submitted a work testing minimal phorias, using a new device, while having participants standing on different surfaces.

Several methods are employed in clinical practice to assess possible phorias, under different conditions [https://www.mdpi.com/2411-5150/8/4/62]. Unfortunately, at least one standard method, that should be used as a reference is missing herein. Multiple testing, probably on different days, or after rest intervals could be adopted. How the authors came with the new device?

Regarding the manuscript, the reader may be confused about the topic, and where is the focus; on the new method, on the surface, or on the potential anatomical circuitry. Cases or pathologies that could provide clues about these conditions are missing. Commentaries on the prevalence, nature and particularities of vertical vs horizontal alignment, and the small pD range are necessary as well [https://pmc.ncbi.nlm.nih.gov/articles/PMC3625960/, https://pubmed.ncbi.nlm.nih.gov/9797992/, https://pubmed.ncbi.nlm.nih.gov/39618986/].

The introduction may seem quite long and segmented. There is a reference to RF, then the structure is revisited many paragraphs later. The presentation of the anatomical parts is tabulated like, and somehow off specialty, it could be part of the discussion. It would be more important to included works on optometry, such as that of Marini et al [https://pmc.ncbi.nlm.nih.gov/articles/PMC11676230/], and rehabilitation.

Overall, the manuscript is in need of paragraph rearrangements and improvement.

L93 durometer -> hardness

L88 to L89 Which authors?

L143 all these studies: the above studies?

2.1 There is a need to include specifics of duration, location and possibly approval body and decision details.

L176 It is to note,

standing mat

L311 comma, reformat

L315 The justification is not clear

Author Response

Replies and changes in the text from Reviewer 1 are in red and Reviewer 2 are in blue

Reviewer #2

R: We thank the reviewer for this insightful comment. The Maddox test, a standard clinical method for evaluating vertical heterophoria, was used as the reference for our measurements. This information has now been added to the Methods section for clarity. The plantar stimulation device was following prior work on plantar mechanoreceptor stimulation and postural regulation (Roll et al., 2002; Maurer et al., 2006). All trials were performed in a single session with short rest intervals between conditions to prevent fatigue and sensory adaptation. These details have been added to strengthen the methodological transparency of the study.

R: We thank the reviewer for this important point. To clarify the study’s focus and provide greater clinical and anatomical context, we revised the Introduction to emphasize that the primary objective of the study was to validate a novel method for rapid, high-precision detection of vertical heterophoria (VH) under different plantar sensory conditions.

Additionally, we incorporated a discussion of the differences between vertical and horizontal phorias, their prevalence, and the clinical relevance of small prism diopter (pD) variations, as suggested by the reviewer. While no pathological groups were included in this study, we clarified that this approach may have future clinical relevance for populations with vestibular or postural disorders.

R: We appreciate the reviewer’s observation regarding the length and segmentation of the Introduction. In response, we have condensed the neuroanatomical description of the reticular formation and related structures, transferring key mechanistic points to the Discussion section for better flow. The Introduction has been rewritten to focus on the clinical and functional context of the study, highlighting the relationship between plantar sensory input, ocular alignment, and postural control. As suggested, the detailed description of the reticular formation and related structures has been relocated to the Discussion section. This new paragraph integrates the neuroanatomical context with our empirical findings, emphasizing the possible neural pathways linking plantar afferents and oculomotor control.

L93 durometer -> hardness

L88 to L89 Which authors?

L143 all these studies: the above studies?

2.1 There is a need to include specifics of duration, location and possibly approval body and decision details.

L176 It is to note,

standing mat

L311 comma, reformat

L315 The justification is not clear

Thank you also for the bibliographical references and suggestions for improvement, which we have incorporated into the text.

Reviewer 3 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Author Response

Dear Editor/ Dear authors

Thank you for inviting me to review the study titled “Does Stimulation of Plantar Mechanoreceptors Alter Visual Spatial Localization?” The aim of this study was to investigate heterophoria in healthy individuals by altering plantar tactile input using a prototype measurement device. A 4-mm thick foam plate and a plate equipped with 1-mm pins were employed to modify tactile stimulation of the foot. According to the authors the findings of the study showed that orthophoric participants developed measurable heterophoria when standing on either the foam or the pin plate, whereas individuals who initially presented with heterophoria shifted toward orthophoria under the same conditions. The prototype device demonstrated high sensitivity, proving to be a fast and user-friendly tool capable of detecting even subtle changes in heterophoria.

From the literature cited in the Introduction section, the study appears to offer originality primarily through the use of a spiked floor, since the effects of foam surfaces have already been well documented. However, this alone cannot constitute the main objective, as the entire investigation depends on measurements obtained from the newly developed heterophoria-detection device.

Yet the authors present the introduction of this device only as a secondary objective, creating a mismatch between the stated aims and the true methodological foundation of the study.

R: Thank you for this important observation. We agree that the aims required clarification. From a methodological perspective, it would have been preferable to prioritise the newly developed heterophoria detection device in this article. As this was not the initial objective of the research, only a single measurement was taken. Furthermore, an alternative measurement tool with a gold standard device (e.g. scleral coil eye tracker) was not utilised. Consequently, it is not possible to assess the reproducibility and validity of the device. However, it is imperative to undertake the validation of the system in a subsequent publication.

In the revised version, we have restructured the final part of the Introduction to clearly state that the main objective of the study was to investigate how subtle stimulation of plantar mechanoreceptors affects VH in healthy adults, using a new measurement device designed to detect small VH values (<1/2 prism diopter) quickly and precisely.

The authors should provide a stronger justification for investigating the effects of the spike plate, particularly in contrast to the already known effects of the foam plate and reinforce the rationale for using the proposed device.

R: To respond to the relevant request, we propose adding the following justifications

While the impact of placing foam [Patel et al., 2008] and fine hard reliefs [Okubo et al., 1980 ; Viseux et al., 2019] under the soles of the feet on postural control is well documented, only the impact of foam on heterophoria has been investigated [Loureau et al. 2023 ; Alessandria, 2022 ; Garrigues, 2007 ; Desennes et Schoenstein, 1996]. Therefore, it appears worthwhile to evaluate the effect of plantar reliefs on phoria and compare it to the effect of foam.

In addition, several essential aspects expected of a newly introduced measurement device, such as demonstrating validity, and reliability.

R: As this was not the initial objective of the research, only a single measurement was taken. Furthermore, an alternative measurement tool with a gold standard device (e.g. scleral coil eye tracker) was not utilised. Consequently, it is not possible to assess the reproducibility and validity of the device. However, it is imperative to undertake the validation of the system in a subsequent publication.

Alternatively, (and from a more fundamental standpoint),

This study may be more appropriately interpreted as an investigation of the construct validity of the proposed heterophoria-detection device (which is my prevailing opinion). Although the device is presented as a secondary objective, it is clearly the central innovation, with the foam and spike plates serving primarily as controlled perturbations to test its responsiveness. Reframing the study around the validation of the device would resolve the mismatch between the stated aims and the actual contribution and would more accurately highlight the significant scientific value of the work. A potential revised title, should the authors choose to adopt this perspective, could be: “Construct Validity of an Innovative Measurement Device for Detecting Subtle Changes in Heterophoria.”

In either case, the authors should take the following comments into consideration before the manuscript can be considered for publication.

Introduction

Lines 45-67: These paragraphs discuss postural control, sensory integration, and the neurological pathways involved in eye–head–trunk–foot coordination. As these topics are not directly aligned with the primary scope of the study, the authors should consider reducing their length.

R: We propose to remove the lines 55-59

The authors suggest that the superior colliculus (SC) would be responsible for whole-body shifts that relay information to the cerebellum. Note also that the cerebellum has been found to play a significant role in the coordination of the head and of the eyes [5], as well as in the whole-body gaze shifts involving stepping [6]. It is involved in the response of central pattern generators (CPG) in the brainstem during motor learning [7].

Lines 68-97: These paragraphs address the influence of plantar stimulation on visual perception. The authors should also consider justifying their choice of alternative methods of modifying visual perception, such as the use of pin-based stimulation.

R: To respond to the relevant request, we propose adding the following justifications

Cavanaugh et al. (2017) posit that the foam has the capacity to reduce pain through the activation of a central pain-modulatory system. The phenomenon of pain inhibition may be attributable to alterations in free nerve endings. In contrast, studies have demonstrated that the application of pressure through the use of reliefs can induce a change in posture, which is a consequence of plantar mechanoreceptor stimulation [Viseux et al., 2019; Okubo et al., 1980].

The hypothesis that the foam has the capacity to inhibit mechanonociceptors and the reliefs has the capacity to stimulate mechanoreceptors suggests the possibility of two kinds of reaction on phoria.

Lines 98-146: These paragraphs offer a detailed explanation of the neuroanatomical pathways linking plantar afferents to visual and oculomotor control. However, the authors should consider summarizing them into a shorter, more concise paragraph.

R: We thank the reviewer for this constructive observation. We agree that the section between lines 98–146 contained excessive detail on the neuroanatomical pathways linking plantar afferents to visual and oculomotor control that were not directly linked to the experimental protocol. In the revised manuscript, this section has been rewritten to provide a clearer justification for the design of the foot stimulation conditions.

Lines 147-156: Before these paragraphs, the authors should justify the need for a new, easy-to-use device for determining minimal vertical heterophoria (VH).

R: To respond to the relevant request, we propose adding the following lines

A substantial body of research has previously been conducted on posturological pathologies using the Maddox test. The findings of this research indicated that the VH value was less than 1 pD [14, 45-49]. The evaluation of heterophoria generally entails the utilization of a Berens prism bar, a device that facilitates the quantification of the deviation angle between the two eyes. The structure of the bar generally consisted of approximately 15 prisms of varying powers. The smaller prism (1 pD) does not permit precise evaluation of these small VH (< 1 pD). A novel device was developed: a circular box that can be used to assess the smallest of heterophorias with minimal time and effort.

In addition, the current text (Line 156) incorrectly refers to this as “HV,” which should be corrected.

R: Thank you for pointing out this error, which we are correcting in the manuscript.

The authors should consider moving some of the information currently presented in the Discussion section (Lines 324–341), particularly the content addressing the clinical significance of diagnosing heterophoria quickly and easily, into the Introduction. This would help to better justify the relevance and necessity of the proposed device earlier in the manuscript.

R: To respond to the relevant request, we propose to move the following lines into the Introduction

As sight specialists are well aware, heterophorias are associated with a variety of symptoms, including but not limited to: blurred and double vision, eye strain, eye pain, retro-ocular pain, photophobia, headaches, motion sickness, and instability [54, 59].

Methods

Line 159: The line should start with words. Please replace “95” with «Ninety-five».

R: Thank you for pointing out this error, which we are correcting in the manuscript.

Furthermore, the authors should provide anthropometric measurements of the participants (e.g., body mass, height).

R: We appreciate your feedback and are addressing directly in the manuscript.

Line 167-177: The authors should consider moving some of the information presented in this paragraph to the Introduction section to justify the relevance and necessity of the proposed device.

R: This paragraph is introduce in the introduction

In 1890, Maddox [10], a strabismus surgeon [40], developed a test commonly used in ophthalmology to assess oculomotor imbalances. This test dissociates the vision of both eyes and makes it possible to objectify ocular deviations. To perform the MT, you need a Maddox rod and a point source of light. This test is a reference in ophthalmology because of its great simplicity [41], rapidity, and reproducibility [42-44]. MT has also been proven helpful in posturology, for detecting minimum heterophoria (< 1pD), mainly vertical heterophoria (VH) in functional disorders such as non-specific chronic pains [45-47] and developmental dyslexia [14, 48, 49]. Note, however, that ophthalmological literature considers VH less than 0,5 diopter to be physiological [50].

Line 200: The authors state that participants stood in a dark room during testing. If the room was indeed dark, it is unclear how participants were able to focus on the light point located at the center of the circular box.

R: Thank you for your request for clarification. We suggest completing the sentence as follows:

The subjects are situated in a darkened room, yet they are able to discern the circular box and the concentric circles within it.

Additionally, the term “light point” is ambiguous: in this section/paragraph it appears to refer simply to a point of light (which would be appropriate in a dark environment), whereas on line 185 it is described as a “light yellow point,” implying a color painted stimulus. The authors should clarify the lighting conditions and ensure consistent terminology regarding the visual target.

R: Thank you for pointing out this error, which we are correcting in the manuscript.

Line 202: It is unclear who held the red glass in a vertical plane during the measurements. The authors should clarify this procedure in the Methods section and, if possible, indicate this detail in Figure 2 to improve clarity for the reader.

R: Thank you for your request for clarification. We suggest completing the sentence as follows:

Figure 2. Calculation of the angle and graduation of the deviation of the visual axis measured on the circle box after the interposition of a red filter held by the examiner.

Line 203: Given that participants likely differed in height, the authors should clarify how they ensured that the light point (please see the comment above) was positioned at each participant’s eye level to maintain the primary gaze position.

R: Thank you for your request for clarification. We suggest completing the sentence as follows:

The subject was five meters away from the circular box, its center placed at the subjects' eye level.

Additionally, the term “primary position” should be defined explicitly, as it is not clear from the current description.

R: Thank you for your request for clarification. We suggest to remove the sentence about the primary position

A red glass is held by the examiner in a strictly vertical plane otherwise the horizontal line may appear curved. The light point is at eye level so that the gaze is in the primary position. To evaluate the VH of the right eye the experimenter stands in front of and to the right of the subject. He always begins by placing the red Maddox rod filter in front of the subject's right eye.

Lines 207-208: It is not clear whether testing between the two eyes was performed in a randomized order. The authors should clarify the sequence of eye testing and indicate whether randomization was used to avoid order effects.

R: The testing between the two eyes was not performed in a randomized order, like it’s write : he always begins by placing the red Maddox rod filter in front of the subject's right eye. Line 209

Line 221-222: Please include the thickness of the foam plate in the Methods section, as it is stated on page 35 to be 4 mm high.

R: We complete in the manuscript.

Figure 4: The vertical axis in Figure 4 is not explained or labeled, leaving the reader to assume that it represents the percentage of participants. Please clearly state the numerical values represented in the graph, either within the figure itself or in the accompanying caption. In addition, the authors should consider using the same vertical-axis scale across all related figures to facilitate comparison.

R: Thank you for this observation. We clarified in the Methods section and corrected in the Figure 4 and the legend.

Line 258-260: Please re-write the sentence “For the right eye, among the orthophoric subjects, the percentage of heterophoria increased significantly on foam (p < 0.005) and on pins (p < 0.05) compared to the baseline condition.” From the figure it looks like the mean percentage of orthophoric subjects decreased on form and pins.

R: Thank you for this observation. We clarified the text

For the right eye, among the orthophoric subjects, the percentage of orthophoria decreased significantly on foam (p < 0.005) and on pins (p < 0.05) compared to the baseline condition.

Please elaborate.

Discussion

Comments on issues not adequately addressed in the discussion

The authors should consider:

Explain why vertical heterophoria changes may differ between the right and left eyes. This asymmetry is reported in the Results but is neither acknowledged nor discussed in the Discussion section.

R: Thank you for this observation. We propose adding this text

The present study shows that vertical heterophoria changes can be very different between the right and left eyes. This change could be explained by the notion of visual dominance, which means that one eye is more used to seeing than the other.

This sighting dominance is not indicative of superior visual acuity [Pointer et al., 2007].

Regarding the studies on gaze alteration and foot stimulation, Quercia et al. (2015) found no significant differences between postural dysfunction and control groups with respect to ocular dominance. The study also demonstrated that tilting the head toward a shoulder resulted in a substantial change in HV for the majority of children diagnosed with developmental dyslexia.. Alessandria [2022] is only one to find a dominance effect, however, he studied only subjects initially with the right dominant eye, which is different to the present study.

Pepose et al. [2025] demonstrated that ocular dominance will be found in 50% of subjects. Conversely, other studies conducted on emmetropic subjects have yielded no discernible ocular dominance. In the absence of pathological features, an alternating balance between both eyes is generally observed. As indicated by Mapp et al. [2007] and Seijas et al. [2007], this phenomenon is associated with significant variability, both between and within different types of tests. It is important to note that the subjects demonstrates significant lability in function in response to postural stimulation [Loureau et al., 2023; Quercia et al., 2015].

Clarify whether the small percentage changes observed (e.g., 2–3% shifts in orthophoria) are clinically meaningful and justify whether the device possesses the measurement sensitivity required to interpret such minor differences. The authors should also discuss whether these changes exceed expected physiological variability.

R: Thank you for this observation. Our discussion proposals.

Although percentage changes observed (e.g., 2–3% shifts in orthophoria for the right eye) are minimal, they are clinically significant because foam or pins can induce heterophoria in a normal subject with physiologic oculomotor balance and so can be deleterious.

and justify whether the device possesses the measurement sensitivity required to interpret such minor differences

R: Thank you for this observation. Our discussion proposals.

Preliminary studies have identified the minimal unphysiologic threshold measured in HV. This threshold varied from 0.3 pD with scleral coils [Van Rijn et al., 1998], to 1 pD with MT [Casillas Casillas et Rosenfield, 2006], and even 2 pD [Saladin, 1995]. Furthermore, Matheron and Kapoula [2011] and Quercia et al. [2015] examined patients with postural disorders who had developmental dyslexia or chronic low back CLBP, respectively, using MT. To quantify HV, they used very small prisms (0.25, 0.5, and 0.75 pD) and identified the presence of HV (< 1 pD) in both populations. This value clearly separated patients from the control group. The essential feature of this VH is a lability which manifests during specific stimulation of sensory receptors involved in postural regulation [Quercia et al., 2015; Loureau et al., 2023]. The available evidence suggests that the VH may have a postural origin, a hypothesis that is corroborated by the current study. The utilization of a device such as the circular box delineated in this study is advantageous, as it facilitates the measurement of small HVs (0.5 to 1 pD). This approach enables a rapid clinical investigation, thereby highlighting subtle variations in HV.

Elaborate on issues of reliability (e.g., test–retest reliability, inter-rater reliability, and potential sources of measurement error) and address the criterion validity of the method by explaining how it compares to established clinical assessments of heterophoria.

R: As explained above, we are unable to determine reliability; this is one of the limitations of the study.

Justify the clinical or empirical relevance of using a spiked plate, particularly since the effects of foam surfaces are already well documented. The authors should explain why spiked stimulation was selected and whether it engages different sensory pathways or produces effects consistent with theoretical expectations.

R: Thank you for this observation. Our editorial proposals.

While the impact of placing foam [Patel et al., 2008] and fine hard reliefs [Okubo et al., 1980, Viseux et al., 2019] under the soles of the feet on postural control is well documented, only the impact of foam on heterophoria has been investigated [Loureau et al., 2023 ; Alessandria, 2022 ; Garrigues, 2007 ; Desennes et Schoenstein, 1996].

As previously discussed in relation to pain modulation, it can be hypothesized that the foam has the capacity to inhibit mechanonociceptors, and the subtle reliefs (pins) have the capacity to stimulate mechanoreceptors. This suggests the possibility of two kinds of reaction on phoria. Therefore, it appears worthwhile to evaluate the effect of plantar reliefs on phorias and compare it to the effect of foam.

Discuss why small or transient shifts in heterophoria might be clinically significant, or acknowledge that their clinical implications remain uncertain, given the modest magnitude of the observed changes.

R: We propose this discussion

In light of the negligible magnitude of the observed changes in heterophoria, it could be deduced that the findings are non-significant. However, it is noteworthy that other studies employing prisms make the measure have yielded analogous results in the context of postural dysfunction.

In a study by Hirasawa et al. [2016] researchers employed wearable eye-tracking glasses to meticulously record visual fixation behavior on a target, specifically a point mark creating an angle visual angle of 0.43°. The study's participants were students devoid of ophthalmic diseases. The results demonstrated that the frequency of deviation from the fixation target was less than 0.5° in 72.4% of the subjects, with a standard deviation of ±21.9%.

Address potential sources of participant variability, such as baseline postural control, plantar foot sensitivity, and foot morphology, which may influence heterophoria responses.

R: We suggest these supplements.

The variability can be explained by the concept of nociception, which was introduced by Sherrington in 1903 to distinguish it from pain (algesia). Since a plantar nociceptive stimulation (unconscious) has been shown to trigger withdrawal reflexes [Andersen et al., 2001] and alter posture [Villeneuve, 1990]. Foam interposition under the foot has been identified as a key factor in drawing attention to this phenomenon [Foisy et al., 2016; Villeneuve, 1996]. In the present study, only one subject reported mild pain from the pins. We can hypothesize that for others, foam or pins altered the nociception.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I see that you addressed my comments as Reviewer 1 (R1) in the sections highlighted in red. After reviewing the revised manuscript, I noted that Reviewer 2's (R2) comments are in blue, and the sections revised at the authors' discretion are in green. The scope of the revisions based on R2's comments was larger than the scope of the revisions addressing R1's comments. Since the authors made extensive revisions, I decided to review areas beyond the previous review's scope.

The previous review primarily resulted in a "reject" decision for the following four reasons. Therefore, I re-reviewed the revised manuscript using these four points as criteria:

(1) "The purpose of this study is unclear."
I confirmed that revisions clarifying the study's purpose were added to lines 143–153. Compared to the previous manuscript, the study's purpose is now clearer. The revisions that addressed R2's comments on lines 91–142 organized the clinical facts and enhanced the paper's value.

(2) "The statistical analysis methods are inadequate."
I confirmed that the inadequacies in the description of the statistical analysis methods were corrected in Section 2.6 (lines 299–315).

(3) "There are points where the findings obtained diverge from the trends in prior research. "
I confirmed that these were revised appropriately. Specifically, the connection to Okubo's methodology, a prior study cited on line 261, was clarified.

(4) "The definition of 'phoria (phoria value)' is not provided."
I confirmed that the calculation method for phoria value was added to lines 306–309.

The additional blue and green sections are valid and appropriately support the argument. No fatal flaws were identified.

Based on the above, I judge that the current manuscript is acceptable for publication."

Additional comments:
Many areas still require minor revisions. Please have a native English speaker proofread the text and verify the formatting.
- A comma is needed at the end of line 86, but appears to be missing.
- Similarly, the opening double quotation mark at the beginning of line 143 is likely unnecessary.

Author Response

Replies and changes in the text from Reviewer 1 (R1) are in red, Reviewer 2 (R2) are in blue and Reviewer 3 (R3) are in green. In the manuscript, the last changes are highlighted in yellow.

The previous review primarily resulted in a "reject" decision for the following four reasons. Therefore, I re-reviewed the revised manuscript using these four points as criteria:

(2) "The statistical analysis methods are inadequate."
I confirmed that the inadequacies in the description of the statistical analysis methods were corrected in Section 2.6 (lines 299–315).

(4) "The definition of 'phoria (phoria value)' is not provided."
I confirmed that the calculation method for phoria value was added to lines 306–309.

The additional blue and green sections are valid and appropriately support the argument. No fatal flaws were identified.

Based on the above, I judge that the current manuscript is acceptable for publication."

R1 : I would like to express my gratitude for your assistance in enhancing the manuscript and for your approval of the current version for publication.
Please find below the corrected version of the text, including the correction of punctuation.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors provided an updated version of their work clarifying many points.

It is a matter of style, but I would suggest to make another effort to provide a more compact version. At several points, we are facing single sentences, then small paragraphs. In each paragraph, it would be better to have an introductory sentence, then some data supporting this statement, then what is missing, and what is need to be done. That way, it would be easier to conclude and provide a solid paragraph with aims and goals in the end of the first part of the manuscript.

Some of the details of the methodology could again be transposed to the M&M section.

Regarding the Discussion part, we see the integration of diverge data, and references to pathology and eye dominance. To my experience, this confirms the divergent approaches in the field, and the integration, or not, of various tools and technologies. The authors refer to the probable involvement of circuitries, however this "generators" may be further shaped by experience. Thus, the whole picture is getting more complicated. I am just wondering how these findings could align with several gaze stabilization exercises and rehabilitation protocols.

Author Response

Replies and changes in the text from Reviewer 2 (R2) are in blue

The authors provided an updated version of their work clarifying many points.

Some of the details of the methodology could again be transposed to the M&M section.

R2 I am delighted that the reviewer notes updated versions of their work clarifying many points.

I appreciate the suggestion to provide a more compact version. I would like to express my gratitude to the reviewer for their advice. However, due to time constraints, I am unable to undertake a substantial rewrite at this time.

Nevertheless, I avoid a redundant sentence. I will take these valuable insights into consideration for my next publication.

Regarding the inquiry about the potential alignment of these findings with various gaze stabilization exercises and rehabilitation protocols, I regret to inform you that I am unable to offer a comprehensive synthetic response. My expertise lies exclusively in the domain of postural rehabilitation.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Editor/ Dear authors

Thank you for the opportunity to review this manuscript for a second time. The revised version is considerably improved compared to the previous submission. However, the absence of reliability and validity data for the measurement instrument remains a significant limitation, which reduces the overall interpretability and clinical relevance of the reported findings. Additional comments and recommendations are provided below to further strengthen the manuscript prior to a final decision regarding acceptance.

Abstract: The fact that heterohoric subjects become orthophoric with foam and pins is not justified by the results (Lines 35-36, see also more comments below).

Abstract: Although the circular box is described as facilitating rapid detection of small heterophorias, no data are provided on its reliability or validity. Without evidence of measurement accuracy or reproducibility, its routine clinical use and recommendation for assessing postural interventions are premature and should not be overstated.

Introduction. (Line 70 and 92) Please specify the type of instability

Introduction. (Line 78-79) The term “functional disorders” is used ambiguously in this context. Non-specific chronic pain is typically classified as a musculoskeletal condition, whereas developmental dyslexia is a neurodevelopmental disorder. Grouping these entities under a single category without clarification may be misleading and require more precise terminology or justification. Please consider modifying the text accordingly throughout manuscript.

Introduction (Lines 103-104): Please consider re-writing the sentence for more clarity “Seated, only one child was orthophoric, and 56% of the heterophoric children became orthophoric when standing, on a foam plate put under their feet”.

Introduction (Lines 186-187): The authors should revise the sentence, “To achieve this, we developed a new, fast, and precise device that enables clinicians to detect minimal VH values (< 1/2 prism diopter).” Based on the data presented, the claim of “precision” is not supported by experimental evidence (e.g., reliability or measurement error analysis) and therefore constitutes an overstatement. This term should be removed or appropriately qualified unless supporting data are provided.

Figure 4. The data presented in Figure 4 indicate that a small but significant proportion of orthophoric subjects become heterophoric when standing on foam or pins, for both the right and left eye. However, the figure does not clearly convey the corresponding proportion of heterophoric subjects who become orthophoric under these conditions. This should be explicitly clarified in the Results section to adequately support the statements made in the Abstract (Lines 35–36) and in the Discussion (Lines 410–412).

Results: For the hypophoric group, it is unclear whether the difference between baseline (34%) and foam (40%) reached statistical significance, as this is not explicitly stated in the text. In contrast, the value reported for the pins condition (38%) appears to be significant despite being lower than that for foam. Please clarify the statistical significance of these comparisons and confirm the correct interpretation of the results.

Figure 5: The percentages of orthophoric and heterophoric subjects at baseline appear inconsistent between figures. In Figure 4, orthophoric subjects at baseline are reported as 49% (right eye) and 45% (left eye), whereas in Figure 5 they are reported as 47% and 43%, respectively. Similarly, heterophoric subjects are reported as 51% (right) and 55% (left) in Figure 4, but as 48% (right) and 52% (left) in Figure 5. Collectively, the proportions at baseline in Figure 5 appear to be approximately 5% lower than those in Figure 4. Please clarify the source of this discrepancy and confirm which values are correct.

Discussion (Lines 378-402). Eye dominance is discussed as a relevant factor, but participant eye-dominance data are not reported. Please report the distribution (and assessment method) if available and clarify whether it differs by ortho-/heterophoria status.

Discussion (Lines 405-443): The discussion in this section is unclear. The authors have stated that several heterophoric participants became orthophoric; however, this interpretation is not supported by the data presented in the current study. On the contrary, Figure 4 shows that the proportion of orthophoric individuals decreases under both the foam and pins conditions, while the proportion of heterophoric individuals increases. This pattern suggests that both experimental conditions exacerbate heterophoria rather than reduce it. The authors should reconcile this inconsistency between their interpretation and the reported results and revise the text accordingly.

Discussion, (Lines 472-476): The authors should explicitly address the current lack of reliability and validity data for the instrument, particularly given that they indicate system validation will be undertaken in subsequent publication. A clear statement of this limitation is warranted to avoid overstating the present clinical applicability of the device.

Author Response

Replies and changes in the text from reviewer 3 (R3) are in green

Abstract: The fact that heterohoric subjects become orthophoric with foam and pins is not justified by the results (Lines 35-36, see also more comments below).

R3 : Thanks for pointing that out. I'll change the sentence to read as follows:

Heterophoric subjects can increase or decrease their phorias depending on foam or pins and the type of HV.

R3 : Thank you for the comment. I propose to moderate the use of the circular device provided by adding:
we suggest that clinicians use this device to assess the effects of postural interventions, even though it has not yet proven its validity.

Introduction. (Line 70 and 92) Please specify the type of instability

R3 : Thank you for the comment. I propose to add postural before instablity

Thank you for the comment. I propose to avoid the term “functional disorders.”

Thank you for the comment. I suggest changing the sentence as follows

He assessed the children in different postures, first seating, like is usual in ophthalmologic showed only one chid orthophoric (1%). Whereas the majority of the heterophoric children (56% ) became orthophoric when standing on a foam plate put under their feet.

Introduction (Lines 186-187): The authors should revise the sentence, “To achieve this, we developed a new, fast, and precise device that enables clinicians to detect minimal VH values (< 1/2 prism diopter).” Based on the data presented, the claim of “precision” is not supported by experimental evidence (e.g., reliability or measurement error analysis) and therefore constitutes an overstatement. This term should be removed or appropriately qualified unless supporting data are provided.

Thank you for the comment. I remove : precise

R3 : Thank you for pointing that out. I will add the following sentence:

The Foam induces a decrease of percentage of hyperphoric subjects in both eyes, whereas pins drive a decrease of percentage of hypophoric subjects for the right eye and hyperphoric for the left eye.

Results: For the hypophoric group, it is unclear whether the difference between baseline (34%) and foam (40%) reached statistical significance, as this is not explicitly stated in the text.

In contrast, the value reported for the pins condition (38%) appears to be significant despite being lower than that for foam.
Please clarify the statistical significance of these comparisons and confirm the correct interpretation of the results.

R3 : Thank you for pointing that out. I would like to add the following sentence:

For the left eye, all hypophoric subjects (38) increased their hypophoria on foam. Regarding the pins, there was a trend toward increased hypophoria, with the exception of two subjects who demonstrated hyperphorias. This discrepancy could explain why the percentage of subjects with pin conditions is significant, even though it is lower than for foam.

R3 : I appreciate you pointing that out. Please note that I would like to correct Figure 5 and use percentages, as the other figures do.

Discussion (Lines 378-402). Eye dominance is discussed as a relevant factor, but participant eye-dominance data are not reported. Please report the distribution (and assessment method) if available and clarify whether it differs by ortho-/heterophoria status.

You have correctly identified that we have not assessed ocular dominance. This is due to the fact that Quercia and colleagues (2015) found no significant differences in ocular dominance in a study on gaze alteration and foot stimulation. In addition, ocular dominance has been linked to ophthalmologic pathologies; however, these pathologies were excluded in the present study. This phenomenon is associated with significant variability, both between and within different types of tests (Mapp et al., 2003; Seijas et al., 2025). We had think that the level of interest in assessing oculomotor dominance is minimal.

In the present study, ocular dominance was not assessed due to the absence of significant differences in ocular dominance observed in a related study on gaze alteration and foot stimulation [20].

On the contrary, Figure 4 shows that the proportion of orthophoric individuals decreases under both the foam and pins conditions, while the proportion of heterophoric individuals increases. This pattern suggests that both experimental conditions exacerbate heterophoria rather than reduce it. The authors should reconcile this inconsistency between their interpretation and the reported results and revise the text accordingly.

R3 : We would like to express our gratitude for highlighting this ambiguous section. The fact that heterophoric subjects exhibiting fluctuations contingent on phorias type (hypo- or hyperphoria), and too presence or absence of foam and pins, is a subject of perplexity.

To clarify this section we propose to add

The current findings are partially consistent with earlier observations for patients with HV [18, 20, 24]. The patients on foam achieved an orthophoric state. The current study for normal subjects on foam shows a decline in the percentage of hyperphoric subjects, with the majority now classified as orthophoric. However, there has been an increase in the number of hypophoric subjects.

Thank you for the comment. I propose to moderate the use of the circular device provided by adding:

This innovative device is particularly well-suited and useful for assessing small heterophorias, even though it has not yet proven its validity.

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors

Thank you for the opportunity to review the revised version of the manuscript. The authors have satisfactorily addressed all comments raised in the previous revision. One minor issue, however, still requires clarification and response:

Since the authors have chosen to present patient data as percentages in all figures, the study observations should be consistently referred to as percentages throughout the manuscript, including the main text and figure descriptions, to ensure clarity and internal consistency.

Furthermore, the authors should clarify whether the parenthetical value in the sentence on page 14, “For the left eye, all hypophoric subjects (38) increased their hypophoria on foam,” refers to the number of subjects (in which case it should be reported as n = 38) or to the percentage of patients.

Author Response

Dear authors

Dear reviewer,

Thank you again for carefully reading my first paper as a lead author and for taking the time to provide such insightful feedback.

I have incorporated your suggested clarifications into the manuscript and highlighted them in blue.

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