Freshwater harmful algal blooms (HABs) are increasing in number and severity worldwide. These HABs are chiefly composed of one or more species of cyanobacteria, also known as blue-green algae, such as Microcystis and Anabaena. Numerous HAB cyanobacterial species produce toxins (e.g., microcystin and anatoxin—collectively referred to as HAB toxins) that disrupt ecosystems, impact water and air quality, and deter recreation because they are harmful to both human and animal health. Exposure to these toxins can occur through ingestion, inhalation, or skin contact. Acute health effects of HAB toxins have been well documented and include symptoms such as nausea, vomiting, abdominal pain and diarrhea, headache, fever, and skin rashes. While these adverse effects typically increase with amount, duration, and frequency of exposure, susceptibility to HAB toxins may also be increased by the presence of comorbidities. The emerging science on potential long-term or chronic effects of HAB toxins with a particular emphasis on microcystins, especially in vulnerable populations such as those with pre-existing liver or gastrointestinal disease, is summarized herein. This review suggests additional research is needed to define at-risk populations who may be helped by preventative measures. Furthermore, studies are required to develop a mechanistic understanding of chronic, low-dose exposure to HAB toxins so that appropriate preventative, diagnostic, and therapeutic strategies can be created in a targeted fashion.

Fusion Maldevelopment Nystagmus (FMN) is one of the most common subtypes of pathologic nystagmus seen in children. The National Institutes of Health Committee on Eye Movement and Strabismus classification has recommended utilizing a new etiologic description from 2001, replacing the term latent nystagmus. This type of nystagmus has initially been called latent because its severity increases, or became evident when an eye is covered. However, it is now known that true latent nystagmus is rare, with the majority of patients have manifest latent nystagmus seen with both eyes uncovered as identified on eye movement recordings. (Abadi and Scallan 2000) Amblyopia is a neurodevelopmental disorder that occurs due to de-correlated binocular input to the visual cortex. Investigations in non-human primate models have revealed that loss of horizontal binocular connections within area V1 in infancy is the necessary and sufficient cause of FMN. (Tychsen et al. 2010) The new terminology describes the strong correlation with a binocular fusion maldevelopment that occurs during the infancy, like strabismus, amblyopia or any monocular vision deprivation. (Tychsen 1992) Studies by the pediatric eye investigator group have compared part-time occlusion to full-time occlusion and found similar levels of improvement in visual acuity. Thus the current standard of treatment is part-time occlusion ranging from 2-6 hours/eye depending on the severity of amblyopia. (Holmes et al. 2003) The slow phase velocity (SPV) of FMN increases under monocular viewing conditions and therefore in patients with FMN occlusion was initially considered contraindicated because it could enhance the nystagmus intensity or amplitude. (Duke-Elder and Wybar 1973) Successively evidence was provided in a small cohort of patients that a significant improvement of visual acuity was obtained with full-time patching during all waking hours. (von Noorden al. 1987) Similarly, Simonsz demonstrated a compensatory drift changes in nystagmus direction and lower magnitude over days of full-day occlusion in 5 patients with latent nystagmus.(Simonsz 1989) Despite good compliance, up to 40% of children treated by occlusion therapy have residual amblyopia. Some baseline risk factors that predict the presence of residual amblyopia include severe amblyopia at time of diagnosis and older age at treatment initiation. (PEDIG Group 2011) Amblyopes are known to have increased fixation instability.(Niechwiej-Szwedo et al. 2012; Subramanian et al. 2013). This instability could be due to the presence of FMN. Amblyopic patients without nystagmus have an increase in the amplitude of fixational saccades with increase inter-saccadic drift, which contributes to the instability in both the fellow and amblyopic eye. (Shaikh et al 2016; Shi et al 2012; Chen et al 2018)In the current manuscript, we characterized the fixational eye movement waveforms of amblyopic patients. We hypothesize that the presence of FMN and increase slow phase velocity in patients with nystagmus would predict treatment respo...

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.