Not only amblyopic but also dominant eye in subjects with strabismus show increased saccadic latency

Abstract

Amblyopia is a developmental disorder of vision usually associated with the presence of strabismus and/or anisometropia during early childhood. Subject literature has shown that both the amblyopic and fellow eyes (especially in strabismic subjects) may manifest a variety of perceptual and oculomotor deficits. Previous studies using simple saccadic responses (pro-saccades) showed an increased saccadic latency only for the amblyopic eye viewing conditions. So far, there have appeared no saccadic latency studies in strabismic amblyopia for more complex volitional saccades. In order to maximize the contribution of the central retina in the process of saccade initiation, we decided to use delayed saccadic responses in order to test the hypothesis about saccadic latency increase in both eyes in strabismic amblyopes. The results from our study have shown that saccadic latency is increased both in the dominant and amblyopic eyes. In addition, the amblyopic eye in the strabismic group showed greater increase in saccadic latency compared to an amblyopic eye in the anisometropic group from our previous study. The observed increase in saccadic reaction time for the dominant eye is novel and provides further evidence that the visual pathway associated with the dominant eye might be also impaired in strabismic amblyopia. Since an abnormal binocular input during visual system development may affect gaze stability in both eyes, we speculate that unsteady fixation accompanied with subtle perceptual deficits contribute to an increase in saccadic latency that is observed in the dominant eye. Moreover, it appears that the cortical processes related to saccade decisions are delayed both for amblyopic and fellow eyes in strabismic subjects.

Gap effect and express saccades generation in amblyopia

“…It is commonly known that saccadic reaction time in response to amblyopic eye stimulation is substantially increased as compared to the dominant eye or normal eyes (Ciuffreda, Kenyon, & Stark, 1978;Niechwiej-Szwedo et al, 2012;Perdziak et al, 2014;McKee et al, 2016;Perdziak et al, 2016). In the present study, we have also observed an increased saccadic latency for amblyopic eye viewing that is in agreement with previous research.…”

“…Several previous studies have shown that amblyopia may affect smooth pursuit, fixational eye movements, or fixation stability (Ciuffreda, Kenyon, & Stark, 1979;Gonzalez, Wong, Niechwiej-Szwedo, Tarita-Nistor, & Steinbach, 2012;Subramanian et al, 2013;Chung, Kumar, Li, R. & Levi, 2015;Ghasia, 2015;Shaikh, Otero-Millan, Kumar, & Ghasia, 2016;Kelly, Cheng-Patel, Jost, Wang, & Birch, 2018). In terms of saccadic eye movements, reduced precision of saccade amplitude or increased saccadic reaction time (latency) may be present in amblyopic subjects (Niechwiej-Szwedo, Chandrakumar, Goltz, & Wong, 2012;Perdziak, Witkowska, Gryncewicz, Przekoracka-Krawczyk, & Ober, 2014;McKee, Levi, Schor, & Movshon, 2016;Perdziak, Witkowska, Gryncewicz, & Ober, 2016). However, in the vast majority of previous research, saccadic latency in amblyopic subjects was measured during the classic paradigm in which the peripheral target is switched on simultaneously with an offset of fixation target-there is no gap condition.…”

Unilateral Amblyopia Affects Two Eyes: Fellow Eye Deficits in Amblyopia

“…This paper explored fellow eye deficits in five visual tasks that have been extensively studied in amblyopia. However, children and adults with amblyopia have demonstrated abnormalities in the fellow eye for a range of additional tasks not discussed here: for example, in foveal function, 294 pupillary response amplitudes, 295 fixational eye movement patterns, 296,297 smooth pursuit, 123 saccadic latency, 298 visual evoked potentials to both form and motion stimuli, 226,[299][300][301][302] blur discrimination, 303 global shape perception, 304 orientation adaptation, 305 line bisection, 306 the extraction of threedimensional structure, 307 maximum motion displacement thresholds, 308,309 single-object tracking, 40 multiple-object tracking, 40,41 scene perception, 310 perception of the McGurk effect, 311 and visual decision-making. 312 Many of these visual functions have been assessed during fellow eye viewing in only a handful of studies, so more work is needed to determine how robust these deficits are and the conditions under which they occur.…”

The functional impact of amblyopia

“…While amblyopic eyes show poorer fixation stability than control eyes during both monocular and binocular viewing, fellow eyes have fixation stability comparable to that of controls, both when fixating or under binocular viewing . However, the initiation of tracking pursuits is delayed and saccadic latency of the non‐amblyopic eye can be less accurate than in age‐matched controls …”