OBJECTIVE: Recent work has called into question the ability of visual acuity (VA) to accurately represent changes in visual function in infantile nystagmus (IN). This systematic review investigated factors affecting visual performance in IN, to guide development of suitable alternatives to VA.
METHODS: Included studies used an experimental manipulation to assess changes in visual function in people with IN. Interventional studies, case series and case studies were excluded. Six databases were searched in August 2023. Selection, detection, attrition and measurement bias were assessed. Due to heterogeneous methodologies, narrative synthesis was undertaken.
RESULTS: Eighteen relevant papers were identified, 11 of which complied with the review criteria. Articles were grouped according to the factor manipulated to evoke within-participant changes in performance (motion blur, psychological state, gaze angle or visual crowding). Optotype, image, grating and moving stimuli have been employed under varying lighting conditions and exposure duration.
CONCLUSIONS: Several factors affecting visual performance should be considered when assessing visual function in IN. While maximum VA is a useful metric, its measurement deliberately minimises nystagmus-specific factors such as changes in visual performance with gaze angle and the \'slow to see\' phenomenon. Maximum VA can be measured using the null zone, providing unlimited viewing time, reducing stress/mental load and minimising visual crowding. Gaze-dependent functional vision space is a promising measure which quantifies the impact of the null zone but does not consider temporal vision. Although no complete measurement technique has yet been proven, this review provides insights to guide future work towards development of appropriate methods.

Toxoplasmosis gondii is ubiquitously present on earth and infection, including congenital infection, is common. Neurological, developmental, and ocular effects can be devastating in the congenital toxoplasmosis population. At present, there is no standard, nation-wide neonatal screening for this disease in the United States.
A 17-month-old Caucasian female presented to our institution by way of referral for macular scarring. She was diagnosed with intrauterine growth retardation and born with low birth weight and microcephaly at an outside institution, but no systemic workup was conducted at that time. On ocular examination, she was found to have nystagmus and extensive multifocal chorioretinal pigmented scars involving the macula and peripheral retina in both eyes with fibrous vitreous strands extending between scars in the right eye. Toxoplasmosis immunoglobulin G was found to be highly positive. Magnetic resonance imaging of the brain showed supratentorial intracranial calcifications.
Our patient presented with severe chorioretinal lesions, microcephaly, and nystagmus with a positive immunoglobulin G toxoplasmosis titer. She did not receive any evaluation, including TORCH infectious panel workup, on being born with low birth weight and microcephaly. There are currently no national programs in place for toxoplasmosis to be included in routine neonatal screening, despite the grave sequelae of congenital infection or that studies in other countries have shown cost-effectiveness in early screening and treatment.

Congenital nystagmus (CN) and congenital cataracts are distinct eye diseases and are usually isolated. Cases with CN and congenital cataracts caused by different genes in one family have been rarely reported.
A 27-year-old man presented with CN and congenital cataracts and he underwent cataract extraction 2 weeks after birth. Three years later, he had posterior chamber intraocular lens implantation. The proband\'s mother was only afflicted by bilateral lens opacities. Lensectomy was performed in both eyes at age 15. The proband\'s daughter had bilateral central cataracts and no nystagmus. She had undergone cataract extraction when she was two months old. In this family, 8 affected individuals were affected by bilateral cataracts, and three of them presented with CN. The genetic analysis was performed using a specific Hereditary Ophthalmological Disease Gene Panel on proband and his parents (one of which was a patient). PCR and Sanger sequencing verified the presence of these variants in all members of the family. The novel mutation, c.498-3C > T, in FRMD7 explains why X-Linked recessive inheritance of CN was found in a subset of patients. A heterozygous mutation of the GJA8 gene (c.139G > C), was identified in all patients and thus explains the autosomal dominant pattern of inheritance of congenital cataracts within the family.
This is the first time that FRMD7 and GJA8 gene mutations have been linked to the pathogenesis of a family with both CN and congenital cataracts. The phenomenon of two different genetic patterns coexisting in one family is rare.

Infantile nystagmus is commonly associated with afferent abnormalities that can be detected using a range of investigative modalities. Optical coherence tomography allows high-resolution in vivo imaging of the retina. Recent studies have shown characteristic foveal abnormalities in patients with albinism, PAX6 mutations, and isolated foveal hypoplasia. Arrested development of the fovea leads to foveal hypoplasia, which causes reduction in visual acuity. Previous studies have shown correlations between visual acuity and the degree of foveal hypoplasia. Furthermore, in achromatopsia a characteristic lesion has been described that is associated with cone photoreceptor degeneration. Patients with achromatopsia also have foveal hypoplasia, however with atypical features. The signs of photoreceptor degeneration were progressive, which suggests that gene therapy is likely to be most beneficial if given within the first few years of life. With the advent of high speed and ultrahigh resolution optical coherence tomography it is now possible to document reliably the stages of foveal development and cone photoreceptor degeneration. This will aid clinicians in diagnosis and predicting prognosis in patients with infantile nystagmus.

Nystagmus is an involuntary, to-and-fro movement of the eyes that can result in a reduction in visual acuity and oscillopsia. Mechanisms that cause nystagmus are better understood in some forms, such as acquired periodic alternating nystagmus, than in others, for example acquired pendular nystagmus, for which there is limited knowledge. Effective pharmacological treatment exists to reduce nystagmus, particularly in acquired nystagmus and, more recently, infantile nystagmus. However, as there are very few randomized controlled trials in the area, most pharmacological treatment options in nystagmus remain empirical.

Congenital Idiopathic Nystagmus (CIN) is genetically heterogeneous. Autosomal dominant, autosomal recessive and X-linked patterns of inheritance have been reported. Linkage analysis has suggested the existence of at least three distinct loci for both autosomal dominant and X-linked forms, although only one disease gene has been identified (FRMD7, Xq26.2). The pathophysiological mechanisms underlying nystagmus are poorly understood but it is anticipated that characterization of the FRMD7 gene and identification of novel nystagmus genes will provide insights into this condition and the functioning and development of the visual pathways in general.

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