Response to spectral-domain optical coherence tomography foveal morphology as a prognostic factor for vision performance in congenital aniridia

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Our current understanding of clinical characteristics and the genetics of patients with albinism

Introduction: Albinism is a heterogenous disease with variable phenotypic and genotypic presentations. Diagnosis can be challenging and clinical evaluation strategies vary. Areas covered: This review examines the phenotypic and genotypic characteristics of albinism and discusses evaluation strategies used to assess its variable clinical presentations. Additionally, it explores the challenges faced by clinicians in diagnosing albinism and issues related to genetic testing, interpretation and subsequent counseling of affected patients and their families. It is important to note that although current management of albinism is mainly supportive and focuses on optimizing vision, there are emerging therapies with promising translational benefit. Expert opinion: Ongoing research in the field of albinism is benefiting from recent advances, particularly in retinal imaging and phenotyping. Similarly, access to advanced technologies like next-generation and long-read sequencing has improved diagnostic accuracy for previous cases with missing heritability. Deeper genotyping and phenotyping as well as multicentre collaborative approaches have allowed better understanding of genotype-phenotype correlations. There is still a need for more research on the psychosocial aspects of albinism. Encouraging involvement of patients and the public in determining research priorities in this area is essential for a better understanding of the psychosocial impact on individuals with albinism

Normal and abnormal foveal development

Normal foveal development begins in utero at midgestation with centrifugal displacement of inner retinal layers (IRLs) from the location of the incipient fovea. The outer retinal changes such as increase in cone cell bodies, cone elongation and packing mainly occur after birth and continue until 13 years of age. The maturity of the fovea can be assessed invivo using optical coherence tomography, which in normal development would show a well-developed foveal pit, extrusion of IRLs, thickened outer nuclear layer and long outer segments. Developmental abnormalities of various degrees can result in foveal hypoplasia (FH). This is a characteristic feature for example in albinism, aniridia, prematurity, foveal hypoplasia with optic nerve decussation defects with or without anterior segment dysgenesis without albinism (FHONDA) and optic nerve hypoplasia. In achromatopsia, there is disruption of the outer retinal layers with atypical FH. Similarly, in retinal dystrophies, there is abnormal lamination of the IRLs sometimes with persistent IRLs. Morphology of FH provides clues to diagnoses, and grading correlates to visual acuity. The outer segment thickness is a surrogate marker for cone density and in foveal hypoplasia this correlates strongly with visual acuity. In preverbal children grading FH can help predict future visual acuity

Current and Emerging Treatments for Albinism

Albinism is a group of rare inherited disorders arising from impairment of melanin biosynthesis. The reduction of melanin synthesis leads to hypopigmentation of skin and eyes. A wide range of ophthalmic manifestations arise from albinism, including reduction of visual acuity, nystagmus, strabismus, iris translucency, foveal hypoplasia, fundus hypopigmentation, and abnormal decussation of retinal ganglion cell axons at the optic chiasm. Currently, albinism is incurable, and treatment aims either surgically or pharmacologically to optimize vision and protect skin; however, novel therapies that aim to directly address the molecular errors of albinism, such as L-dihydroxyphenylalanine (L-DOPA) and nitisinone, are being developed and have entered human trials though with limited success. Experimental gene-based strategies for editing the genetic errors in albinism have also met early success in animal models. The emergence of these new therapeutic modalities represents a new era in the management of albinism. We focus on the known genetic subtypes, clinical assessment, existing and emerging therapeutic options for the non-syndromic forms of albinism

Home-based screening tools for amblyopia: a systematic review protocol

Introduction Amblyopia is an important public health concern associated with functional vision loss and detrimental impact on the physical and mental well-being of children. The gold standard for diagnosis of amblyogenic conditions currently involves screening by orthoptists and/or ophthalmologists. The bloom of technology enables the use of home-based screening tools to detect these conditions at an early stage by the layperson in community, which could reduce the burden of screening in the community, especially during restrictions associated with the COVID-19 pandemic. Here, we propose a systematic review aiming to evaluate the accuracy and reliability of home-based screening tools compared with the existing gold standard. Methods and analysis We aim to search for studies involving home-based screening tools for amblyopia among children aged under 18 years. Oxford Centre for Evidence-Based Medicine Level 4 evidence and above will be included, without language or time restrictions. The following platforms will be searched from inception to 31 August 2021: PubMed, Medline, The Cochrane Library, Embase, Web of Science Core Collection and Clinicaltrials.gov. Two independent reviewers will identify studies for inclusion based on a screening questionnaire. The search and screening will start on 14 August 2021 until 1 October 2021. We aim to complete our data analysis by 30 November 2021. Risk of bias will be assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool for diagnostic accuracy studies only. Our primary outcome measure is the diagnostic accuracy of home-based screening tools, while secondary outcome measures include validity, feasibility, reproducibility and cost-effectiveness, where available. Ethics and dissemination Ethical approval is not necessary as no primary data will be collected. The findings will be disseminated through presentations at scientific meetings and peer-reviewed journal publication. PROSPERO registration number CRD42021233511.</div

Longitudinal Evaluation of Changes in Retinal Architecture Using Optical Coherence Tomography in Achromatopsia

PURPOSE. This prospective study investigates longitudinal changes in retinal structure in patients with achromatopsia (ACHM) using optical coherence tomography (OCT).  METHODS. Seventeen patients (five adults, 12 children) with genetically confirmed CNGA3- or CNGB3-associated ACHM underwent ocular examination and OCT over a follow-up period of between 2 and 9.33 years (mean = 5.7 years). Foveal tomograms were qualitatively graded and were segmented for quantitative analysis: central macular thickness (CMt), outer nuclear layer thickness (ONLt), and size of the foveal hyporeflective zone (vertical HRZ thickness: HRZt and horizontal HRZ width: HRZw) were measured. Data were analyzed using linear mixed regression models. Both age and visit were included into the models, to explore the possibility that the rate of disease progression depends on patient age. RESULTS. Fifteen of 17 patients (88%) showed longitudinal changes in retinal structure over the follow-up period. The most common patterns of progression was development of ellipsoid zone (EZ) disruption and HRZ. There was a significant increase in HRZt (P = 0.01) and HRZw (P = 0.001) between visits and no significant change in CMt and ONLt. Retinal parameters showed no difference in changes by genetic mutation (CNGA3 (n = 11), CNGB3 (n = 6)).  CONCLUSIONS. This study demonstrates clear longitudinal changes in foveal structure mainly in children, but also in adults with ACHM, over a long follow-up period. The longitudinal foveal changes suggest that treatment at an earlier age should be favored.</p

ERG Responses in Albinism, Idiopathic Infantile Nystagmus, and Controls

PurposeOur primary aim was to compare adult full-field ERG (ffERG) responses in albinism, idiopathic infantile nystagmus (IIN), and controls. A secondary aim was to investigate the effect of within-subject changes in nystagmus eye movements on ffERG responses.MethodsDilated Ganzfeld flash ffERG responses were recorded using DTL electrodes under conditions of dark (standard and dim flash) and light adaptation in 68 participants with albinism, 43 with IIN, and 24 controls. For the primary aim, the effect of group and age on ffERG responses was investigated. For the secondary aim, null region characteristics were determined using eye movements recorded prior to ffERG recordings. ffERG responses were recorded near and away from the null regions of 18 participants also measuring the success rate of recordings.ResultsFor the primary aim, age-adjusted photopic a- and b-wave amplitudes were consistently smaller in IIN compared with controls (P ConclusionsAge-adjusted photopic ffERG responses are significantly reduced in IIN adding to the growing body of evidence of retinal abnormalities in IIN. Differences between photopic responses in albinism and controls depend on age. Success at obtaining ffERG responses could be improved by recording responses at the null region

SLC38A8 mutations result in arrested retinal development with loss of cone photoreceptor specialisation.

Foveal hypoplasia, optic nerve decussation defects and anterior segment dysgenesis is an autosomal recessive disorder arising from SLC38A8 mutations. SLC38A8 is a putative glutamine transporter with strong expression within the photoreceptor layer in the retina. Previous studies have been limited due to lack of quantitative data on retinal development and nystagmus characteristics. In this multi-centre study, a custom-targeted next generation sequencing (NGS) gene panel was used to identify SLC38A8 mutations from a cohort of 511 nystagmus patients. We report 16 novel SLC38A8 mutations. The sixth transmembrane domain is most frequently disrupted by missense SLC38A8 mutations. Ninety percent of our cases were initially misdiagnosed as PAX6-related phenotype or ocular albinism prior to NGS. We characterized the retinal development in vivo in patients with SLC38A8 mutations using high-resolution optical coherence tomography. All patients had severe grades of arrested retinal development with lack of a foveal pit and no cone photoreceptor outer segment lengthening. Loss of foveal specialization features such as outer segment lengthening implies reduced foveal cone density, which contributes to reduced visual acuity. Unlike other disorders (such as albinism or PAX6 mutations) which exhibit a spectrum of foveal hypoplasia, SLC38A8 mutations have arrest of retinal development at an earlier stage resulting in a more under-developed retina and severe phenotype