Effect of Viewing Conditions on Fixation Eye Movements and Eye Alignment in Amblyopia

Abstract

Purpose Patients with amblyopia are known to have fixation instability, which arises from alteration of physiologic fixation eye movements (FEMs) and nystagmus. We assessed the effects of monocular, binocular, and dichoptic viewing on FEMs and eye alignment in patients with and without fusion maldevelopment nystagmus (FMN). Methods Thirty-four patients with amblyopia and seven healthy controls were recruited for this study. Eye movements were recorded using infrared video-oculography during (1) fellow eye viewing (FEV), (2) amblyopic eye viewing (AEV), (3) both eye viewing (BEV), and (4) dichoptic viewing (DcV) at varying fellow eye (FE) contrasts. The patients were classified per the clinical type of amblyopia and FEM waveforms into those without nystagmus, those with nystagmus with and without FMN. Fixational saccades and intersaccadic drifts, quick and slow phases of nystagmus, and bivariate contour ellipse area were analyzed in the FE and amblyopic eye (AE). Results We found that FEMs are differentially affected with increased amplitude of quick phases of FMN observed during AEV than BEV and during DcV at lower FE contrasts. Increased fixation instability was seen in anisometropic patients at lower FE contrasts. Incomitance of eye misalignment was seen with the greatest increase during FEV. Strabismic/mixed amblyopia patients without FMN were more likely to demonstrate a fixation switch where the AE attends to the target during DcV than patients with FMN. Conclusions Our findings suggest that FEM abnormalities modulate with different viewing conditions as used in various amblyopia therapies. Increased FEM abnormalities could affect the visual function deficits and may have treatment implications.

Assessment of binocular fixational eye movements including cyclotorsion with split-field binocular scanning laser ophthalmoscopy

“…Seeing with two eyes, that is, binocularity, is central to human visual processing. For instance, ocular controls of the retinal image forming process, like pupil constriction and accommodation, are highly coupled between the two eyes ( Flitcroft, Judge & Morley, 1992 ), and ocular motor commands issued to control gaze of one eye are tightly coupled to those of the fellow eye ( Tweed, 1997 ; Murray, Gupta, Dulaney, Garg, Shaikh & Ghasia, 2022 ), for example, during the tracking of a moving object. Less is known whether this tight coupling extends to the phases of stable fixation, where fixational eye movements (FEM) predominate ( Krauskopf, Cornsweet & Riggs, 1960 ; Simon, Schulz, Rassow & Haase, 1984 ; Otero-Millan, Macknik & Martinez-Conde, 2014 ).…”

Eye Tracking to Assess the Functional Consequences of Vision Impairment: A Systematic Review

“…36,37 Similar results were found in amblyopic patients, where fixation stability was impaired, more so in the amblyopic eye, and with the amount of instability increasing commensurate with increases in the severity of the amblyopia. 20,26,38 This instability was accompanied by increased velocities and amplitudes of fixational eye movements such as drifts and (micro)saccades. 20,38 Paradigm II: Smooth Pursuit…”

“…20,26,38 This instability was accompanied by increased velocities and amplitudes of fixational eye movements such as drifts and (micro)saccades. 20,38 Paradigm II: Smooth Pursuit…”

“…Despite the potential complications when tracking the eyes of individuals with vision impairment, it seems, based on recent publications, [19][20][21] that eye tracking is increasingly being used to evaluate functional vision in the presence of vision impairment. Recent studies have, for instance, reported delayed saccadic latencies in individuals with glaucoma, 13 diminished fixation stability in amblyopic individuals, 20 and reduced performance in pursuing a moving stimulus in those with macular degeneration, 21 when compared with healthy control participants. However, it may be that those studies are evaluating only a subset of people with vision impairment by focusing on those with ocular conditions that are less likely to impact the quality of eye tracking.…”

Assessment of binocular fixational eye movements including cyclotorsion with split-field binocular scanning laser ophthalmoscopy

“…binocularity, is central to human visual processing. For instance, ocular controls of the retinal image forming process, like pupil constriction and accommodation, are highly coupled between the two eyes (Flitcroft, Judge & Morley, 1992), and ocular motor commands issued to control gaze of one eye are tightly coupled to those of the fellow eye (Tweed, 1997; Murray, Gupta, Dulaney, Garg, Shaikh & Ghasia, 2022), for example during tracking of a moving object. Less is known whether this tight coupling extends to the phases of stable fixation, where fixational eye movements (FEM) predominate (Krauskopf, Cornsweet & Riggs, 1960; Otero-Millan, Macknik & Martinez-Conde, 2014; Simon, Schulz, Rassow & Haase, 1984).…”