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The amblyopic eye in subjects with anisometropia show increased saccadic latency in the delayed saccade task.

Perdziak M, Witkowska D, Gryncewicz W, Przekoracka-Krawczyk A, Ober J - Front Integr Neurosci (2014)

Bottom Line: The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination.Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood.By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Oculomotor Research, Department for Biophysical Measurements and Imaging, Nałęcz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences Warsaw, Poland.

ABSTRACT
The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination. Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood. Several studies have shown prolongation of saccadic latency time in amblyopic eye. In our opinion, study of saccadic latency in the context of central vision deficits assessment, should be based on central retina stimulation. For this reason, we proposed saccade delayed task. It requires inhibitory processing for maintaining fixation on the central target until it disappears-what constitutes the GO signal for saccade. The experiment consisted of 100 trials for each eye and was performed under two viewing conditions: monocular amblyopic/non-dominant eye and monocular dominant eye. We examined saccadic latency in 16 subjects (mean age 30 ± 11 years) with anisometropic amblyopia (two subjects had also microtropia) and in 17 control subjects (mean age 28 ± 8 years). Participants were instructed to look at central (fixation) target and when it disappears, to make the saccade toward the periphery (10°) as fast as possible, either left or the right target. The study results have proved the significant difference in saccadic latency between the amblyopic (mean 262 ± 48 ms) and dominant (mean 237 ± 45 ms) eye, in anisometropic group. In the control group, the saccadic latency for dominant (mean 226 ± 32 ms) and non-dominant (mean 230 ± 29 ms) eye was not significantly different. By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.

No MeSH data available.


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Latency distribution (plotted as a reciprobits) for selected controls.
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Figure 9: Latency distribution (plotted as a reciprobits) for selected controls.

Mentions: The supply of information to the visual system can be considered in two dimensions: the speediness and equally important correctness/completeness and both are required for effective saccades programming. For this reason we interpret our finding on the basis of reduced rate of rise of neural activation in the cells involved in saccade initiation for amblyopic eye viewing. As we will discuss in more detail later, the rate of rise of neural activation represents the rate of rise of the decision signal, which (according to the Carpenter's LATER decision model) depends on the rate of information supply to the visual system. We have applied the distributional analysis carried out by means of reciprobit plot, and combined it with the LATER model (Carpenter, 1988; Wardak et al., 2012), in order to plot, compare and interpret the changes in the saccadic reaction time for subjects with anisometropic amblyopia. To the best of our knowledge this the first study that makes such an effort. Neurophysiological evidences supporting the Carpenter's model comes from the studies on rhesus monkeys. Hanes and Schall (1996) studied neural activity of single cells in the FEF, an area that plays a central role in production of voluntary saccades. They reported that neural activity of the cell began to increase ~100 ms before the saccade initiation and peaked shortly after saccade initiation. Saccadic eye movements were initiated only if the neural activity reached a specific and constant threshold level (Hanes and Schall, 1996). The study by Hanes and Schall (1996) has revealed the population of saccadic movement-related neurons, whose activity corresponds closely with the rise-to-threshold of LATER's decision signal (Hanes and Schall, 1996; Reddi et al., 2003). According to the LATER model, the neural signal rises linearly in each trial from an initial level SO to a threshold level ST, which initiates the saccade. The rate of rise varies randomly between trials in a Gaussian fashion with mean μ (Reddi et al., 2003). Based on the 100 saccadic responses for each eye, we found significant decrease in mean (μ) rate of rise in anisometropic group (Figure 6) during amblyopic eye viewing, evidenced by the rightward parallel shift of corresponding reciprobit plots (Figure 8). This may be interpreted as a difference in supply of information (decrease in accumulation of visual information) acquired by means of the central retina, that delays the saccade execution decision. In the control group, the mean rate of rise was not significantly different between the eyes (Figure 6), evidenced by the superposition of the corresponding reciprobit plots (Figure 9). Figure 10 presents the subject without any detectable visual problems, however we reported surprisingly significant difference in saccadic latency between the eyes (manifested by the significant increase of mean latency for non-dominant eye). We cannot exclude the situation that this subject was not properly motivated during experimental procedure because when we re-examined this subject several weeks later there were no differences in saccadic latency between the eyes.


The amblyopic eye in subjects with anisometropia show increased saccadic latency in the delayed saccade task.

Perdziak M, Witkowska D, Gryncewicz W, Przekoracka-Krawczyk A, Ober J - Front Integr Neurosci (2014)

Latency distribution (plotted as a reciprobits) for selected controls.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4196517&req=5

Figure 9: Latency distribution (plotted as a reciprobits) for selected controls.
Mentions: The supply of information to the visual system can be considered in two dimensions: the speediness and equally important correctness/completeness and both are required for effective saccades programming. For this reason we interpret our finding on the basis of reduced rate of rise of neural activation in the cells involved in saccade initiation for amblyopic eye viewing. As we will discuss in more detail later, the rate of rise of neural activation represents the rate of rise of the decision signal, which (according to the Carpenter's LATER decision model) depends on the rate of information supply to the visual system. We have applied the distributional analysis carried out by means of reciprobit plot, and combined it with the LATER model (Carpenter, 1988; Wardak et al., 2012), in order to plot, compare and interpret the changes in the saccadic reaction time for subjects with anisometropic amblyopia. To the best of our knowledge this the first study that makes such an effort. Neurophysiological evidences supporting the Carpenter's model comes from the studies on rhesus monkeys. Hanes and Schall (1996) studied neural activity of single cells in the FEF, an area that plays a central role in production of voluntary saccades. They reported that neural activity of the cell began to increase ~100 ms before the saccade initiation and peaked shortly after saccade initiation. Saccadic eye movements were initiated only if the neural activity reached a specific and constant threshold level (Hanes and Schall, 1996). The study by Hanes and Schall (1996) has revealed the population of saccadic movement-related neurons, whose activity corresponds closely with the rise-to-threshold of LATER's decision signal (Hanes and Schall, 1996; Reddi et al., 2003). According to the LATER model, the neural signal rises linearly in each trial from an initial level SO to a threshold level ST, which initiates the saccade. The rate of rise varies randomly between trials in a Gaussian fashion with mean μ (Reddi et al., 2003). Based on the 100 saccadic responses for each eye, we found significant decrease in mean (μ) rate of rise in anisometropic group (Figure 6) during amblyopic eye viewing, evidenced by the rightward parallel shift of corresponding reciprobit plots (Figure 8). This may be interpreted as a difference in supply of information (decrease in accumulation of visual information) acquired by means of the central retina, that delays the saccade execution decision. In the control group, the mean rate of rise was not significantly different between the eyes (Figure 6), evidenced by the superposition of the corresponding reciprobit plots (Figure 9). Figure 10 presents the subject without any detectable visual problems, however we reported surprisingly significant difference in saccadic latency between the eyes (manifested by the significant increase of mean latency for non-dominant eye). We cannot exclude the situation that this subject was not properly motivated during experimental procedure because when we re-examined this subject several weeks later there were no differences in saccadic latency between the eyes.

Bottom Line: The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination.Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood.By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.

View Article: PubMed Central - PubMed

Affiliation: Laboratory for Oculomotor Research, Department for Biophysical Measurements and Imaging, Nałęcz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences Warsaw, Poland.

ABSTRACT
The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination. Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood. Several studies have shown prolongation of saccadic latency time in amblyopic eye. In our opinion, study of saccadic latency in the context of central vision deficits assessment, should be based on central retina stimulation. For this reason, we proposed saccade delayed task. It requires inhibitory processing for maintaining fixation on the central target until it disappears-what constitutes the GO signal for saccade. The experiment consisted of 100 trials for each eye and was performed under two viewing conditions: monocular amblyopic/non-dominant eye and monocular dominant eye. We examined saccadic latency in 16 subjects (mean age 30 ± 11 years) with anisometropic amblyopia (two subjects had also microtropia) and in 17 control subjects (mean age 28 ± 8 years). Participants were instructed to look at central (fixation) target and when it disappears, to make the saccade toward the periphery (10°) as fast as possible, either left or the right target. The study results have proved the significant difference in saccadic latency between the amblyopic (mean 262 ± 48 ms) and dominant (mean 237 ± 45 ms) eye, in anisometropic group. In the control group, the saccadic latency for dominant (mean 226 ± 32 ms) and non-dominant (mean 230 ± 29 ms) eye was not significantly different. By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.

No MeSH data available.


Related in: MedlinePlus