Fixational eye movement waveforms in amblyopia: Characteristics of fast and slow eye movements

Abstract

Fixational eye movements comprise of fast microsaccades alternating with slow inter-saccadic drifts. These physiologic eye movements play an important role in visual perception. Amblyopic patients are known to have fixation instability, particularly of the amblyopic eye. We examined eye movement abnormalities that contribute to this instability. We found that fixation stability is affected by the presence of fusion maldevelopment nystagmus (FMN). However, some amblyopes can have nystagmus without nasally directed slow phases and reversal in direction of the quick phase on ocular occlusion, features seen in FMN. In patients without nystagmus, we found increased amplitude of fixational saccades and inter-saccadic drifts. We categorized amblyopia patients by type (anisometropic, strabismic, or mixed) and eye movement waveform (no nystagmus, nystagmus without FMN, and FMN). We found specific fast and slow eye movement abnormalities of the fellow and amblyopic eye during fellow, amblyopic and both eyes viewing conditions across eye movement waveforms and types of amblyopia. These eye movement abnormalities can serve as biomarkers that can predict the impact of amblyopia as measured by visual acuity and stereopsis. Evaluation of fixational eye movements in amblyopia could be important to diagnose these common eye diseases and predict treatment effectiveness.

Monocular and Binocular Visual Function Deficits in Amblyopic Patients with and without Fusion Maldevelopment Nystagmus

“…20 The FEM traces of the patients were classified based on the presence or absence of nystagmus (Figure 1). 14 Like control subjects, patients without nystagmus (NN-Figure 1A) exhibited inter-saccadic drifts between fixational saccades. 14,21 Patients with nystagmus were further divided into those with FMNS (Figure 1B) versus those that did not meet the criteria of FMNS (Figure 1C).…”

“…14 Like control subjects, patients without nystagmus (NN-Figure 1A) exhibited inter-saccadic drifts between fixational saccades. 14,21 Patients with nystagmus were further divided into those with FMNS (Figure 1B) versus those that did not meet the criteria of FMNS (Figure 1C). The presence of FMNS was determined based on the reversal in nystagmus direction observed under alternate eye monocular viewing such that slow phases of decreasing or constant velocity are nasally directed with respect to the viewing eye.…”

“…3,12 Increased fixation instability is seen in the FE and AE of patients with anisometropic and/or strabismic amblyopia, albeit to a greater degree in the AE, than in controls. 13,14 We have shown that this instability arises from the presence of nystagmus or due to alterations in physiologic fixation eye movements (FEM), namely fixational saccades and inter-saccadic drifts in patients without nystagmus. 13,14 Poor stereo-acuity and worse visual acuity deficits are seen in the AE of patients with greater fixational instability.…”

“…13,14 We have shown that this instability arises from the presence of nystagmus or due to alterations in physiologic fixation eye movements (FEM), namely fixational saccades and inter-saccadic drifts in patients without nystagmus. 13,14 Poor stereo-acuity and worse visual acuity deficits are seen in the AE of patients with greater fixational instability. [13][14][15] The relationships between FEM characteristics and amblyopia type on visual functions of the FE and AE have not been investigated in the same cohort.…”

“…13,14 Poor stereo-acuity and worse visual acuity deficits are seen in the AE of patients with greater fixational instability. [13][14][15] The relationships between FEM characteristics and amblyopia type on visual functions of the FE and AE have not been investigated in the same cohort.…”