Eye movements are the natural, smooth, coordinated, and effortless ability of the human eye to move, maintaining a sharp, fused, and focused image at the center of the retina. This ability has been studied since the early 20th century.1 Eye movements must be efficiently integrated and can occur automatically with the involvement of the lower and frontal areas of the brain, without requiring direct intervention from the frontal lobe. This allows the frontal lobe to focus on tasks such as learning, attention, and comprehension.2

Oculomotor skills are used to predict the actions of objects and other people, helping to anticipate actions for protection or reaction.3 Smooth pursuits and saccades are two fundamental types of eye movements used to characterize eye motion dynamics. Smooth pursuits are voluntary eye movements, characterized by being slow, fluid, and coordinated between both eyes, allowing the image to remain stable on the fovea as stimuli move across the visual field.4

Saccades are rapid eye movements that help fixate on an object and bring it to the center of the retina. These movements can reach speeds between 100 and 800° per second, with an average frequency of 100,000 saccades per day.5,6

There are different types of saccadic movements: memory-guided, antisaccades, and visually guided. The latter are divided into recovery saccades, anticipatory movements, and regression movements (movements made toward the target but failing slightly, followed by a correction saccade). Saccade gain is the ratio between the actual saccadic amplitude and the desired saccadic amplitude. If the gain is <1, the saccade will be too small, which is known as a hypometric saccade.7 One the other hand, when the gain is greater than 1, the saccade will be too large, known as a hypermetric saccade.

Additionally, oculomotor performance plays a key role in organizing a wide variety of everyday activities, such as walking, driving, and cooking, and is essential for the development of reading. Oculomotor dysfunction can potentially lead to problems in these areas.8,9 Therefore, in optometric examinations, evaluating eye movements should be considered a crucial component, with particular emphasis on saccadic movements. It has even been suggested that eye movement analysis could serve as an additional tool to help diagnose certain oculomotor dysfunctions.10

Several studies have shown that neurological diseases11 and neurodevelopmental disorders (NDD), such as dyslexia, attention deficit hyperactivity disorder (ADHD), and developmental coordination disorder (DCD), can affect eye movements.12 Difficulties in the precision and execution of saccadic eye movements have been identified in all three types of NDD.12,13 In the case of children with ADHD, difficulties were found in the ability to inhibit oculomotor responses.14,15 For children with DCD, there were challenges in maintaining fixation and tracking moving objects, as well as a higher frequency of errors in anti-saccades.16

The objetive of this study is to explore saccadic eye movements in children across three age groups: group 1 (7–8 years), group 2 (9–11 years), and group 3 (12–13 years). The study compares the outcomes obtained using two assessment methods: the subjective Northeastern State University College of Optometry (NSUCO) Oculomotor test and an objective analysis using the Tobii Eye X Eye Tracker. Furthermore, saccadic eye movements in children with oculomotor dysfunction (ODG) are preliminarily compared with those of a control group (CG).

This research aims to provide useful insights into the evaluation of eye movements in pediatric clinical practice. By comparing a traditional subjective method with a novel objective technology, the study highlights the potential for integrating accessible tools like NSUCO with more advanced techniques. Such comparisons can contribute to more accurate and comprehensive assessments of oculomotor function in children, especially in cases where access to eye-tracking technology is limited.

The objetive of this pilot study was to explore saccadic eye movements in children using two different assessment tools: the subjective NSUCO test and an objective eye-tracking system. In addition, performance was compared between children with oculomotor dysfunction and a control group, and potential age-related differences were analyzed across three age groups. Despite the small sample size, preliminary results indicate that both assessment methods were able to detect differences in saccadic performance. Furthermore, some age-related trends were observed, suggesting that age may influence oculomotor function.

The established diagnostic criteria for oculomotor dysfunction have yet to be validated on a large scale. Maples et al.13 attempted this with the NSUCO, which specifically evaluates the saccades. One drawback is the influence of factor such as the examiner's need for control, the language barriers or the patient's attention. To address these limitations, research has focused on using eye tracking to eliminate biases introduced by the examiner's subjectivity.19,20 However, the ability to assess the saccadic remains crucial, as has already been demonstrated.12,13,15,17,20–23

In light of the results obtained, differences were found between the CG and ODG across all three age groups and in all categories assessed with the NSUCO, with worse values in the group with oculomotor dysfunction. This indicates significant differences in oculomotor assessment scores between children with oculomotor impairments and normative populations. Similar findings have been reported in several studies.12,14,15

Additionally, it is observed that in all three assessed categories, both in the CG and ODG, older age is associated with better ability, greater precision, and fewer head movements, although these improvements are less pronounced in the ODG compared to the CG. These findings align with those of Maples et al.,13 which explain the development and standardization of the NSUCO test and establish a correlation between age and test performance. Similarly, studies by Fukushima et al.24 and Stewart et al.25 suggest that the precision of initial saccadic movements is greater in adults than in children.

Likewise, in our study, the percentage and number of hypometric and hypermetric saccades are higher in the ODG across all age groups, with a greater increase in older children. In this group, the percentage of regressions also increases with age. This finding is noteworthy because, according to Rayner et al.26 and Blythe et al.27,28 regressions tend to decrease with age. This aligns with the observation that patients with oculomotor dysfunction tend to exhibit more regressions.

Blignaut et al. (2019)20 objectively compared the correlation between the two tests and found that the Eye Tracker has greater sensitivity in detecting hypometric and hypermetric saccades, as well as smaller deviations compared to subjective tests. Additionally, the same study reports a strong correlation between objective and subjective systems. This may explain the lack of significance in saccadic ability and precision observed in age group 3 with the NSUCO.

In group 1 (ages 7 to 8),NSUCO ability was negatively correlated with the number and percentage of hypometric saccades in 0.5-second intervals. Walker et al. (2019)29 found that children with sensory processing disorder (SPD) exhibit deficient oculomotor skills compared to children with typical development. However, for a 1-second interval, NSUCO ability was positively correlated with the number and percentage of complete saccades and negatively with the percentage of hypermetric saccades. Sinno et al.30 reported normative values for saccades and smooth pursuit in children aged 5 to 17 years, observing that saccadic accuracy improves with age, which supports the positive correlation with complete saccades and negative correlation with hypermetric saccades. These results are consistent, as a low score in NSUCO ability and precision indicates that the patient performs fewer complete saccades, leading to a higher number of hypometric and hypermetric saccades.

In group 2 (ages 9 to 11), a moderate correlation was found between the three NSUCO skills and the percentage of regressions with 1-second latencies, especially in individuals with a higher number of head movements. Namaeh et al.31 provided normative data for objective measures of vergence and saccades in children aged 9 to 17, highlighting the importance of accuracy and latency in assessment. Furthermore, in this group, the number of hypometric saccades in 1 s was correlated with NSUCO accuracy.

In group 3 (ages 12 to 13), a strong correlation was found between saccadic ability assessed with the NSUCO and the number of complete saccades for a 1-second stimulus interval. In this group, NSUCO precision was positively correlated with both the number and percentage of complete saccades for the same interval. Bucci et al.32 studied the development of horizontal saccades in children aged 6 to 15 years, finding that saccadic accuracy improves significantly with age, which supports the strong correlation found in our study.

Similar results were found in a study by Bilbao et al.,23 which analyzed a sample of children aged 6 to 12 with oculomotor dysfunction. Specifically, a correlation was observed between saccadic ability, precision, and reduced head/body movements in cases with a higher percentage of regressions.

Combining subjective tests such as the Northeastern State University College of Optometry (NSUCO) test with eye-tracking technology can offer a more comprehensive and practical evaluation strategy for assessing saccadic eye movements by leveraging the strengths of both approaches while mitigating their individual limitations.

Subjective tests like the NSUCO test are accessible, quick to perform, and easy to integrate into clinical practice. They rely on examiner judgment to assess saccadic performance, which can be beneficial for initial screenings and in settings where advanced technology is not available. However, these tests can be limited by their subjective nature and potential variability between examiners.

Eye-tracking technology, on the other hand, provides a detailed and quantifiable analysis of saccadic behavior. It offers objective measurements of parameters such as latency, peak velocity, and accuracy, which are crucial for diagnosing and monitoring neurological conditions.33 For instance, the study by Demian et al. established evaluative standards using video oculography (VOG) to objectively measure saccadic parameters across different age groups, highlighting the utility of such technology in clinical settings.33,34 Similarly, Kullmann et al. demonstrated the reliability of portable eye-tracking devices in assessing oculomotor and cognitive functions, further supporting their clinical application.

By combining these methods, clinicians can benefit from the rapid and accessible nature of subjective tests for initial assessments and use eye-tracking technology for detailed, objective analysis when needed. This hybrid approach allows for a more thorough evaluation of saccadic eye movements, enhancing diagnostic accuracy and patient care while addressing the limitations of each method individually.

This study presents several limitations that should be acknowledged. First, the overall sample size was small, with a particularly small control group, raising concerns about its representativeness and limiting the generalizability of the findings. Additionally, group 3 had a very limited number of participants, which may have affected statistical significance, increased variability, and reduced the statistical power of the comparative analyses.

Another important limitation is the lack of explicit information regarding the number of participants with and without oculomotor dysfunction within each of the three age groups. This information is crucial for interpreting the findings and should be clearly reported in future research.

Although neurodevelopmental disorders were not an exclusion criterion, we acknowledge that detailed diagnoses were not systematically recorded. This allowed for a more representative sample but may have introduced variability affecting oculomotor outcomes. Future studies should collect this information in a standardized.

It should also be noted that group 2 included participants across three different age ranges, while groups 1 and 3 each spanned only two, potentially introducing additional heterogeneity. Furthermore, the use of subjective tests inherently carries the limitation of examiner bias, which may have influenced the outcome interpretation.

We acknowledge that dividing the sample into three age groups further reduced the number of participants per group, limiting the statistical power to detect age-related differences. Nevertheless, this stratification was intentionally applied to reflect the developmental trajectory of oculomotor control in childhood, as supported by previous research. Despite the inherent constraints of a pilot study, this grouping allowed for a preliminary exploration of age-related patterns, which may help guide future studies aiming to establish age-specific normative data.

Given the variability observed in the results and the limited sample size of this pilot study, future research should include a formal sample size calculation and significantly increase the number of participants. This would help to enhance statistical power, improve the reliability of findings, and strengthen the diagnostic validity of both subjective and objective assessment tools. Additionally, it would be valuable to include other complementary tests, such as the DEM test, to explore correlations between different oculomotor assessment methods in pediatric populations.

As age increases, the skill and precision of saccadic movements improve, and head movements decrease, with lower scores observed in the group with oculomotor dysfunctions. Furthermore, hypometric saccades and regressions are consistent indicators of oculomotor dysfunction, regardless of age. These can be detected using objective eye tracking analysis, as well as the subjective NSUCO test, which is easy to implement in clinical settings.

This study is the first, to our knowledge, to demonstrate a significant correlation between objective oculomotor analysis obtained through an Eye Tracker system and the subjective NSUCO test. In fact, oculomotor parameters derived from the Eye Tracker can be predicted based on the categories evaluated by the NSUCO subjective test. This finding has important clinical implications, confirming the validity of the NSUCO as a quick and effective method for assessing eye movements in children with oculomotor dysfunctions and healthy children, especially when Eye Tracker technology is not available due to economic or logistical constraints.

Conceptualization, C.B., R.H.A. and D.P.P.; methodology, C.B., R.H.A., ACB. and D.P.P.; formal analysis, D.P.P.; investigation, C.B., ACB. and D.P.P.; resources, C.B. and D.P.P.; data curation, C.B., ACB. and D.P.P.; writing—original draft preparation, C.B., J-O.C-M.; writing—review and editing, C.B., R.H.A., ACB., D.P.P. and J-O.C-M.; supervision, D.P.P.. All authors have read and agreed to the published version of the manuscript.

No funding for this study.