Idiopathic infantile nystagmus (IIN) is a genetically heterogeneous disorder, often associated with FRMD7 mutations. As the appearance of the retina is reported to be normal based on conventional fundus photography, IIN is postulated to arise from abnormal cortical development. To determine whether the afferent visual system is involved in FRMD7 mutations, we performed in situ hybridization studies in human embryonic and fetal stages (35 days post-ovulation to 9 weeks post-conception). We show a dynamic retinal expression pattern of FRMD7 during development. We observe expression within the outer neuroblastic layer, then in the inner neuroblastic layer and at 9 weeks post-conception a bilaminar expression pattern. Expression was also noted within the developing optic stalk and optic disk. We identified a large cohort of IIN patients (n = 100), and performed sequence analysis which revealed 45 patients with FRMD7 mutations. Patients with FRMD7 mutations underwent detailed retinal imaging studies using ultrahigh-resolution optical coherence tomography. The tomograms were compared with a control cohort (n = 60). The foveal pit was significantly shallower in FRMD7 patients (P < 0.0001). The optic nerve head morphology was abnormal with significantly decreased optic disk area, retinal nerve fiber layer thickness, cup area and cup depth in FRMD7 patients (P < 0.0001). This study shows for the first time that abnormal afferent system development is associated with FRMD7 mutations and could be an important etiological factor in the development of nystagmus.

Aims To characterise longitudinal progressive retinal changes in achromatopsia. Methods Ultrahigh-resolution spectral optical coherence tomography (Copernicus, 3 μm axial resolution) was used to obtain tomograms of the fovea from five children and three adults with achromatopsia. Each patient was scanned twice with a mean follow-up time of 16 months. Progressive changes in reflectivity at the inner segment/outer segment (IS/OS) junction, the central macular and outer nuclear layer thickness were analysed. Results Younger patients (40 years; patients 6–8) did not have any changes in the retinal morphology between visits 1 and 2. In patients 1 and 2, IS/OS discontinuities (visit 1) developed into a hyper-reflective zone confined to the fovea (visit 2). In patient 3, the hyper-reflective zone (visit 1) progressed to form an IS/OS disruption and early formation of a small hypo-reflective zone (visit 2). Patients 4 and 5 had a hypo-reflective zone (visit 1) which subsequently increased in size (visit 2). There was a decrease in central macular and outer nuclear layer thickness between visits 1 and 2 in children. Conclusions For the first time, we show progressive longitudinal changes in retinal morphology in achromatopsia. Early changes include subtle IS/OS reflectivity alterations. The dynamic retinal changes in younger patients provide evidence that it represents a progressive disorder, and implementation of gene therapy during the early stages of the disease may provide best prognosis.

To characterise the genotypic and phenotypic spectrum of foveal hypoplasia (FH) Multi-centre, observational study 907 patients with a confirmed molecular diagnosis of albinism, PAX6, SLC38A8, FRMD7, AHR or achromatopsia (ACHM) from twelve centres in nine countries (n=523), or, extracted from publicly available datasets from previously reported literature (n=384). Individuals with a confirmed molecular diagnosis and availability of foveal optical coherence tomography (OCT) scans were identified from twelve centres or from the literature, between January 2011 and March 2021. A genetic diagnosis was confirmed by sequence analysis. Grading of FH was derived from OCTs. Grade of FH, presence or absence of photoreceptor specialisation (PRS+ vs PRS−), molecular diagnosis and visual acuity (VA). The most common genetic etiology for typical FH in our cohort was albinism (67.5%), followed by PAX6 (21.8%), SLC38A8 (6.8%) and FRMD7 (3.5%) variants. AHR variants were rare (0.4%). Atypical FH was seen in 67.4% of ACHM cases. Atypical FH in ACHM had significantly worse VA compared to typical FH (p<0.0001). There was a significant difference in the spectrum of FH grades based on the molecular diagnosis (X²=60.4, p<0.0001). All SLC38A8 cases were PRS− (p=0.003), while all FRMD7 cases were PRS+ (p<0.0001). Analysis of albinism sub-types revealed a significant difference in the grade of FH (X²=31.4, p<0.0001) and VA (p=0.0003) between oculocutaneous albinism (OCA) compared to ocular albinism (OA) and Hermansky-Pudlak syndrome (HPS). OA and HPS demonstrated higher grades of FH and worse VA than OCA. There was a significant difference (p<0.0001) in VA between FRMD7 variants compared to other diagnoses associated with FH. We characterised the phenotypic and genotypic spectrum of FH. Atypical FH is associated with much worse prognosis compared to all other forms of FH. In typical FH, our data suggests that arrested retinal development occurs earlier in SLC38A8, OA, HPS and AHR variants and much later in FRMD7 variants. The defined time-period of foveal developmental arrest for OCA and PAX6 variants appears to demonstrate more variability. Our findings provide mechanistic insight into disorders associated with FH and also have significant prognostic and diagnostic value.