Urban nature-based solutions as public-health infrastructure: a scoping review of implemented interventions.

Amblyopia is a neurodevelopmental disorder caused by binocular discordant input during the critical period, most commonly from anisometropia, strabismus, or early visual deprivation, and is characterized by reduced visual acuity in one eye. Although strabismus may occur with or without amblyopia, both conditions share sensory sequelae such as impaired stereoacuity and interocular suppression, which are frequently accompanied by oculomotor abnormalities, including fixation instability. Prior work from our laboratory and others has demonstrated that fixation instability is increased in the viewing eye of amblyopic patients, whereas instability in the nonviewing eye is commonly attributed to disrupted binocular coordination resulting from ocular misalignment. It reflects abnormalities in physiologic fixation eye movements—enlarged fixational saccades and increased intersaccadic drifts. In strabismus, increased instability in the nonviewing eye is often attributed to ocular misalignment. Another major contributor to fixation instability in these populations is fusion maldevelopment nystagmus (FMN; historically termed ), a pathologic nystagmus arising from early binocular disruption and characterized by conjugate, predominantly horizontal slow phases with nasalward drift relative to the viewing eye, reversal with fixation switch, and augmentation during monocular viewing or occlusion. Importantly, FMN occurs in both strabismic amblyopia and strabismus without amblyopia. Despite its clinical relevance, no prior studies have systematically dissociated fast and slow fixation eye movement (FEM) abnormalities in amblyopic and strabismic patients with and without FMN across binocular and monocular viewing conditions. Further, most prior studies have quantified fixation instability primarily using time domain metrics, a limitation given that FMN introduces structured, oscillatory dynamics that may be incompletely captured by conventional time domain measures alone. Consequently, how amblyopia severity interacts with FMN to alter foveation periods—brief intervals of reduced retinal slip that are essential for effective visual sampling—remains unclear. In addition, binocular fixation instability implicates dysfunction of vergence pathways. Under normal conditions, fixation disparity between the two eyes remains within fusion-tolerant limits that support stereopsis, whereas strabismus and reduced binocularity are associated with increased disconjugacy. FMN likely represents a more severe manifestation of early binocular and vergence maldevelopment. Yet whether FMN is associated with disproportionate binocular disconjugacy, and how this relationship depends on amblyopia severity and viewing condition, has not been established. The present study uniquely quantifies eye-specific fast and slow FEM dynamics across viewing conditions, enabling mechanistic separation of amblyopia severity–dependent effects, ocular misalignment, and FMN. We also complemented conventional FEM metrics with foveation and frequency domain analyses to more fully characterize FMN-related fixation dynamics. We hypothesize that amblyopia is characterized by interocular asymmetric abnormalities in FEMs, with greater instability in the amblyopic eye, whereas such asymmetries are absent in strabismus without amblyopia. Furthermore, we posit that increasing amblyopia severity in patients with FMN will be associated with reduced foveation and progressively abnormal fixation dynamics, with strabismic amblyopia and FMN reflecting more severe disruption of early binocular and vergence development. The study protocols were approved by the Cleveland Clinic Institutional Review Board, and written informed consent was obtained from each participant or their parent/legal guardian, in accordance with the Declaration of Helsinki. A total of 161 participants (65 males, 96 females) were recruited, comprising 64 healthy controls. All participants underwent comprehensive eye exams, including visual acuity, cycloplegic refraction, ocular motility assessment, strabismus evaluation, and stereoacuity measurements using the Titmus Stereoacuity Test. Control participants were chosen based on the absence of any ocular or systemic abnormalities affecting visual acuity, except for refractive errors. Amblyopia was defined as reduced corrected distance visual acuity without structural abnormalities of the optic nerve, retina, or visual pathways. Patients in the amblyopic cohort demonstrated at least a two-line difference in visual acuity between the two eyes at the time of diagnosis. Patients were classified as having anisometropic and strabismic amblyopia based on criteria established by the PEDIG studies. Anisometropic amblyopia was defined based on meeting at least one of the following criteria: ≥0.50-D difference between both eyes in spherical equivalent or ≥1.50-D difference between both eyes in astigmatism at any meridian ( = 30). Strabismic amblyopia based on meeting at least