Vergence and Accommodation Cues in Stereo-Localization during the Small-In Large-Out (SILO) Effect
Round 1
Reviewer 1 Report
When performing Vision therapy patients are asked to maintain fusion during the treatment. In the cases when convergence demand is increased, target image will start appear smaller and on the other hand when the need for divergence reflex is increased the target object will appear bigger (SILO effect). Authors of this paper used localization of the target image in the space in comparison with AC/A relation to determine the relationship between vergences and accommodative clues, and the stereo localization accuracy.
Taking into consideration prolonged time spent on the computers and near work in modern way of living additional analyses of the elements included in near work that can improve visual and intellectual performance are very important. The method described in this paper is comparing two different reflexes that are measured using standard orthoptic methods and calculating results using geometrical and mathematical formulas to assists in the understanding of the physiological basis of the vision therapy.
The fact that vision therapy will be more and more important as the method of choice for the problems caused by prolonged near work is giving importance to this paper. This work is making vision therapy more accepted and better understood which enables and encourages medical experts for it's more often and more precise use. The paper is well structed and because of the importance off the topic worth publishing.
In my opinion the weakness of this work is that although the well-known elements are combined and calculated in interesting and new way nothing new is proven.
Participants are well recruited with important exclusion criteria included in the process.
It is not clearly described if the measurements of stereovision are performed at near or distant.
Author Response
When performing Vision therapy patients are asked to maintain fusion during the treatment. In the cases when convergence demand is increased, target image will start appear smaller and on the other hand when the need for divergence reflex is increased the target object will appear bigger (SILO effect). Authors of this paper used localization of the target image in the space in comparison with AC/A relation to determine the relationship between vergences and accommodative clues, and the stereo localization accuracy.
Taking into consideration prolonged time spent on the computers and near work in modern way of living additional analyses of the elements included in near work that can improve visual and intellectual performance are very important. The method described in this paper is comparing two different reflexes that are measured using standard orthoptic methods and calculating results using geometrical and mathematical formulas to assists in the understanding of the physiological basis of the vision therapy.
The fact that vision therapy will be more and more important as the method of choice for the problems caused by prolonged near work is giving importance to this paper. This work is making vision therapy more accepted and better understood which enables and encourages medical experts for it's more often and more precise use. The paper is well structed and because of the importance off the topic worth publishing.
RESPONSE: Thank you for the kind appraisal of our work. Indeed, one of our main aims was to provide evidence to some of the procedures commonly employed in vision therapy, and improve our understanding of the governing mechanisms.
In my opinion the weakness of this work is that although the well-known elements are combined and calculated in interesting and new way nothing new is proven.
RESPONSE: We appreciate this comment in order to improve the discussion of this work. Usually, the SILO effect is explained in some books, such as Scheiman & Wick (Scheiman, Mitchell, and Bruce Wick. Clinical management of binocular vision: heterophoric, accommodative, and eye movement disorders. Lippincott Williams & Wilkins, 2008) as an important part in vision therapy when employing procedures based on vectograms and/or anaglyphs. It is usually explained as a graphical example. This study tries in to analyse this effect with a mathematical approac, opening new avenues for research in this topic. Secondly, the exact visual or perceptual processes that produce the SILO effect have not been described yet, to our knowledge. This study shows that vergence and accommodation cues might have an effect in the correct stereo-localization of the target stimulus, but only under 10 BO, not with BI, or even 5 BO demands. The discussion provided about the possible asymmetries in vergence systems (convergence and divergence), as well as the perceptual changes in retinal size, aims at providing a better understanding of this particular procedure, with a practical application in clinics. These findings, further explored in future research, could help the clinician conducting vision therapy to better manage their patients. Besides, future work in patients with binocular dysfunctions, such as convergence insufficiency, and comparing the response in SILO (or SOLI) according to visual parameters such NPC, AC/A or amplitude of accommodation, could provide additional relevant information in this particular topic. We have added a few sentences to the Discussion of the manuscript to better reflect the novelty of this research (lines 189-193).
Participants are well recruited with important exclusion criteria included in the process.
RESPONSE: Thank you for this comment.
It is not clearly described if the measurements of stereovision are performed at near or distant.
RESPONSE: Stereovision was measured at near distance (40 cm) with the Random Dot test. We have added this information to the revised manuscript (line 85).
Reviewer 2 Report
The revision is in the attached pdf.
Comments for author File: 
Comments.pdf
Author Response
The topic of this draft is interesting. However, since no (strong) reference is given to a critical issue, it needs vital clarifications before going for a complete revision. All the 2.2 section needs to be clarified, which may (eventually) affect all the further sections deeply. Thus, the authors need to explain the following issues before going further in the revision.
RESPONSE: Thank you for this comment. We have edited the section 2.2 to improve the description of our methodology.
It is difficult for a reader to understand Figure 1, particularly the red and blue triangles, and derive equation 1. Maybe it helps with a simple one, like the sketch shown below.
Given the geometric setup shown in this sketch and by referring to the intercept theorem, the relation between the mentioned geometric entities are similar to Equations (1) but unfortunately not equal, i.e.:
d = (41.35 * IPD/2)/((IPD/2) + x) and d’ = (41.35 * IPD/2)/((IPD/2) - x)
RESPONSE: We would like to express our gratitude to the reviewer for this careful revision of our calculations. Indeed, the reviewer is correct and the formula should be as noted (x, not 2x). Initially we used IPD and 2x for our calculations, instead of IPD/2 and x (which is the same as we are dividing by 2 both numerator and denominator). Somehow the 2x was erroneously kept in the formulas we included in the manuscript, albeit the calculations were correctly done using x (half the separation between vectograms). Therefore, the following data description and analysis is correct.
To improve clarity of presentation, we have uploaded a new image following the suggestions of the reviewer. Thank you!
Round 2
Reviewer 2 Report
Some comments to the authors that might help improve the present manuscript
Line 15: remove “novel”
Line 20: add “worse accuracy” to “stereo-localization accuracy”, i.e., “stereo-localization accuracy (i.e., worse accuracy)”
Line 85 -86: “near point of convergence (NPC), measured 3 times with the aid of a Royal Air Force rule” what do authors do with these three measurements? a mean? a median?
Line 119: define what “m” and “s” represent in formula (2)
Table 1. Check whether Near Phoria (0.4 m) is eso (i.e. positive)
Line 162-164: CoV can provide a relative measure of the repeatability in some variables. However, its usage in variables where scale values (thus the mean) can be on either side of the zero represents a mathematical indeterminacy (when the mean is zero) and has an odd interpretation when the CoV assumes negative values. Therefore, I suggest removing the reference to CoV.
Line 178-179: delete “(top left: 5Δ BO; top right: 10Δ BO; bottom 178 left: 5Δ BI; bottom right: 10Δ BI)” because it is already in the Figure (duplicate information).
Line 181: delete “analysis”
Line 182-delete “top left: 5Δ BO; top right: 10Δ BO; bottom left: 5Δ BI; bottom right: 10Δ BI”
Line 198-199: “worse under divergence than convergence conditions” according to the results, this is inaccurate because 10∆ BI is also worse than 5∆ BI. Please repair.
Line 201-205: It is difficult for the reader to follow the statement, “For instance, Hung and coworkers noted that the slope of the peak velocity versus the amplitude curve was higher for convergence than divergence, and observed a larger amplitude of the initial fast component for convergence for divergence, suggesting that neural processing delays and controller pathways are different for convergence and divergence [18].” This statement should be auto-explained; what peak velocity versus the amplitude curve refers to? It needs context.
Line 204: “for convergence for divergence” repair
Line 212: Replace “but not” with “but not so in”
Line 227: “stimulus and response” is not clear to the reader what is the “stimulus” what is the “response”.
Line 250-251: “In addition, the AC/A ratio was also found to influence stereo-acuity, with patients with higher esophorias at near and lower AC/A ratios showing better accuracy.” This information is not in the results; where does this come from?
Author Response
Line 15: remove “novel”
Line 20: add “worse accuracy” to “stereo-localization accuracy”, i.e., “stereo-localization accuracy (i.e., worse accuracy)”
RESPONSE: Thank you. We have edited the manuscript according to these comments.
Line 85 -86: “near point of convergence (NPC), measured 3 times with the aid of a Royal Air Force rule” what do authors do with these three measurements? a mean? a median?
RESPONSE: The median of the three repeated measures was obtained. We have added this information to the revised manuscript.
Line 119: define what “m” and “s” represent in formula (2)
RESPONSE: We have added this information to the manuscript (lines 124-126). “where m and m’ correspond to measured distances in convergence and divergence, respectively, and s and s’ to calculated distances in convergence and divergence, respectively.”
Table 1. Check whether Near Phoria (0.4 m) is eso (i.e. positive)
RESPONSE: We have revised the data and, indeed, there was an error, which we have addressed in the revised manuscript. Near phoria was mostly exo (i.e., negative). This error was a simple omission when writing the table, and did not have any effect elsewhere.
Line 162-164: CoV can provide a relative measure of the repeatability in some variables. However, its usage in variables where scale values (thus the mean) can be on either side of the zero represents a mathematical indeterminacy (when the mean is zero) and has an odd interpretation when the CoV assumes negative values. Therefore, I suggest removing the reference to CoV.
RESPONSE: The reviewer is correct. We have deleted the CoV results.
Line 178-179: delete “(top left: 5Δ BO; top right: 10Δ BO; bottom 178 left: 5Δ BI; bottom right: 10Δ BI)” because it is already in the Figure (duplicate information).
Line 181: delete “analysis”
Line 182-delete “top left: 5Δ BO; top right: 10Δ BO; bottom left: 5Δ BI; bottom right: 10Δ BI”
RESPONSE: Figure legends have been edited accordingly.
Line 198-199: “worse under divergence than convergence conditions” according to the results, this is inaccurate because 10∆ BI is also worse than 5∆ BI. Please repair.
RESPONSE: We have rewritten this sentence to improve clarity of presentation (lines 209-211). “Stereo-localization accuracy was found to be worse under divergence than con-vergence conditions, with a mean difference of 13.80 cm and 3.65 cm between theoretical and perceived localization of the target stimulus for 10∆ BI and 5∆ BI, respectively, and of 1.50 and 1.43 cm for 10∆ BO and 5∆ BO, respectively”.
Line 201-205: It is difficult for the reader to follow the statement, “For instance, Hung and co-workers noted that the slope of the peak velocity versus the amplitude curve was higher for convergence than divergence, and observed a larger amplitude of the initial fast component for convergence for divergence, suggesting that neural processing delays and controller pathways are different for convergence and divergence [18].” This statement should be auto-explained; what peak velocity versus the amplitude curve refers to? It needs context.
RESPONSE: We have edited this sentence to avoid technical terms that might not have been familiar to readers (lines 213-216). “Hung and co-workers noted different dynamics for convergence and divergence, in terms of velocity, amplitude and latency, consistent with clinical findings in fusional vergence range assessment, suggesting that neural processing delays and controller pathways are different for convergence and divergence”.
Line 204: “for convergence for divergence” repair
Line 212: Replace “but not” with “but not so in”
RESPONSE: We have edited the manuscript.
Line 227: “stimulus and response” is not clear to the reader what is the “stimulus” what is the “response”.
RESPONSE: We have added a sentence to the manuscript to describe stimulus and response (lines 243-245). “Indeed, AC/A ratio stimulus assumes that change in accommodation is equal to the visual demand, whilst AC/A ratio is computed from the actual response of the accommodation system.”
Line 250-251: “In addition, the AC/A ratio was also found to influence stereo-acuity, with patients with higher esophorias at near and lower AC/A ratios showing better accuracy.” This information is not in the results; where does this come from?
RESPONSE: The reviewer is correct. These findings were part of a larger study not reported in the present manuscript. Accordingly, we have deleted this sentence.
