One of the parameters of eye movement recording devices is their sampling rate. It has been widely studied how the sampling rate of eye trackers affects the assessment of saccadic eye movement parameters. It has also been investigated whether the sampling rate of eye trackers affects the duration of fixations and saccade parameters during reading. In studies analyzing fixation stability, measurements are taken at different sampling rates, but how the sampling rate affects this fixation parameter has not been extensively investigated. Fixation stability is commonly quantified using bivariate contour ellipse areas (BCEA). The aim of this study was to determine whether the sampling rate of an eye tracker affects the measurement of fixation stability. Participants in the study were adults aged 20 to 30 years. Their eye movements during fixation were recorded using the Tobii Pro Fusion eye tracker. The fixation target was presented on a computer monitor, and eye movements were recorded at three sampling rates: 60 Hz, 120 Hz, and 250 Hz. The results demonstrated strong correlation between the BCEA measurements of each participant across all used sampling rates. However, when analyzing the overall data, there is no significant effect of the sampling rate on fixation stability measurement.
Fixation stability is the ability of the eyes to maintain a constant and stable gaze on the fixation target. One of the visual functions that can be affected by unstable fixation is stereopsis. Stereovision is important for a variety of daily tasks, as well as for using stereoscopic displays in visualizations and entertainment, such as watching movies and playing video games. The interaction between fixational stability and stereopsis in different conditions has often been studied in children with amblyopia. The aim of our research is to explore the relationships between binocular fixation stability and stereopsis in school-aged children who do not have amblyopia and strabismus in their anamnesis. The children were divided into two groups: those with normal stereoacuity (≤ 60 arcsec in the TNO test) and those with reduced stereoacuity (≥120 arcsec in the TNO test). The fixation target was demonstrated on a computer screen, and eye movements during fixation were recorded using a Tobii Pro Fusion eye tracker operating at 250 Hz. The results demonstrate that children with better stereoacuity tend to have more stable fixation compared to children with reduced stereoacuity. However, the difference in fixation stability was not significant.
Both in medicine and optometry, clinical guidelines have become a relevant part of clinical practice decision making process. In our study, we aimed to refer to potential limitations related to specific undefined guidelines used in optometry that suggest near addition (add) values based on patient age. We measured near add binocularly at 40 cm distance with plus build up technique in 216 adults aged 35 to 80 years. Baseline subjective refraction, near visual acuity with and without add was analysed in a relation to age and the amount of near add. For further analysis, we randomly selected 30 patients and performed five different near add estimation techniques. Our results support that there is a positive, linear relationship of moderate strength between age and amount of near add (r = 0.73, P < 0.05). Relationship is positive and fairly strong (r = -0.78, P < 0.05) between near visual acuity without add and near add amount and moderate (r = -0.51, P < 0.05) between near visual acuity without add and patient age. Differences between plus build up technique is not statistically significant if compared with other clinical near add estimation techniques (P > 0.05). Guideline based technique (P < 0.01) provided 0.29 D higher near add while technique based on calculations from amplitude of accommodation (P < 0.01) provided 0.65 D lower near add. Based on our results, we highlight that usability of age expected near add in clinical environment is limited because of large individual differences.
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