Retina as a potential biomarker in schizophrenia spectrum disorders: a systematic review and meta-analysis of optical coherence tomography and electroretinography

The Retinal Age Gap as a Marker of Accelerated Aging in the Early Course of Schizophrenia

BACKGROUND AND HYPOTHESIS

Given the available findings confirming accelerated brain aging in schizophrenia (SZ), we conducted a study aimed at verifying whether quantitative retinal morphological data enable age prediction and whether schizophrenia patients present with a positive retinal age gap (RAG).

STUDY DESIGN

Two samples of patients and controls were enrolled: one included 59 SZ patients and 60 controls, all of whom underwent optical coherence tomography (OCT) enabling the measurement of 72 variables. A second sample of 65 SZ patients and 70 controls was then combined with the first sample, to generate a database where each subject was represented by 28 morphological variables. Four different machine learning (ML) algorithms were used for age prediction based on z-standardized OCT data. The associations between RAG, demographic, and clinical data were also analyzed.

STUDY RESULTS

Patients from both samples had significantly higher retinal age and positive RAG ranging between 5.88 and 7.44 years depending on the specific sample. Predictions based on the larger group but with fewer OCT variables exhibited higher prediction relative error. All ML algorithms generated similar outcomes regarding retinal age. RAG correlated with the dose of antipsychotic medication and the severity of symptoms. Correlations with chronological age showed that RAG was the highest in younger patients, and from the age of about 45 years, it decreased.

CONCLUSIONS

ML-based results corroborated accelerated retinal aging in schizophrenia and showed its associations with pharmacological treatment and syndrome severity. The finding of a larger RAG in younger patients is novel and requires replication.

Thinning of central foveal thickness in the retina of patients with schizophrenia

The neural retina shares a common embryonic origin with the brain and yields pathological changes like that in the brain in various neuropsychiatric disorders, including schizophrenia. Non-invasive examination by optical coherence tomography (OCT) revealed retinal structure abnormalities in patients with schizophrenia. This study investigated retina structures in 29 patients with schizophrenia and 25 healthy controls in a Chinese Han ethnic population with spectral domain OCT. Measurements of central foveal thickness (CFT) as well as other retinal structures in macular and peripapillary subregions were performed. Associations between OCT parameters and clinical features, including severity of positive and negative symptoms, disease duration and antipsychotic dosage were analyzed. With controlling for age and sex, patients showed significantly thinner CFT, thinner central macular thickness, and thinner total retinal thickness in subregions of the central, inner superior, inner temporal, and inner nasal macula of both eyes, thinner ganglion cell complex in a subregion of the left eye, as well as larger cup volume in the peripapillary region of the right eye. In addition, CFT also negatively correlated with severity of negative symptoms. These findings suggest that CFT has the potential to be a disease biomarker of schizophrenia.

On the improvement of schizophrenia detection with optical coherence tomography data using deep neural networks and aggregation functions

Schizophrenia is a serious mental disorder with a complex neurobiological background and a well-defined psychopathological picture. Despite many efforts, a definitive disease biomarker has still not been identified. One of the promising candidates for a disease-related biomarker could involve retinal morphology , given that the retina is a part of the central nervous system that is known to be affected in schizophrenia and related to multiple illness features. In this study Optical Coherence Tomography (OCT) data is applied to assess the different layers of the retina. OCT data were applied in the process of automatic differentiation of schizophrenic patients from healthy controls. Numerical experiments involved applying several individual 1D Convolutional Neural Network-based models as well as further using the aggregation of classification results to improve the initial classification results. The main goal of the study was to check how methods based on the aggregation of classification results work in classifying neuroanatomical features of schizophrenia. Among over 300, 000 different variants of tested aggregation operators, a few versions provided satisfactory results.

Retinal Optical Coherence Tomography in Bipolar Disorder: A Scoping Review

BACKGROUND

Bipolar disorder (BD) is a psychiatric condition with significant health implications due to its comorbidities, premature mortality, and functional impairments. Despite extensive research on treatment and rehabilitation, gaps remain in diagnosis and monitoring. Therefore, there is a need for biomarkers to identify individuals at risk for disease progression or exacerbation. Developmentally part of the central nervous system, the retina represents a possible marker for observing BD-related structural and functional alterations in the brain.

SUMMARY

The retina's structure can be assessed through optical coherence tomography (OCT), a noninvasive and cost-effective method. Retinal alterations, particularly in the retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL), have been associated with neurodegenerative and psychiatric disorders in cross-sectional OCT studies. This scoping review discusses findings on retinal changes in BD as well as their association with disease characteristics like symptom severity and illness duration and highlights OCT as a potential diagnostic tool in BD treatment.

KEY FINDINGS

The majority of studies indicate RNFL and GCL thinning in BD patients, which was found to correlate with clinical characteristics in some studies. Although the data are currently limited, there is a possibility that retinal biomarkers could facilitate monitoring of BD, but more research needs to be conducted to observe the relationship between these parameters and BD. Moreover, other factors (e.g., treatment, metabolic and inflammatory conditions) may impact retinal changes, which highlights the need for longitudinal studies to clarify these relationships. Further research should focus on replicating current findings, understanding the role of inflammation, and differentiating between retinal regions affected by BD.

BACKGROUND

Bipolar disorder (BD) is a psychiatric condition with significant health implications due to its comorbidities, premature mortality, and functional impairments. Despite extensive research on treatment and rehabilitation, gaps remain in diagnosis and monitoring. Therefore, there is a need for biomarkers to identify individuals at risk for disease progression or exacerbation. Developmentally part of the central nervous system, the retina represents a possible marker for observing BD-related structural and functional alterations in the brain.

SUMMARY

The retina's structure can be assessed through optical coherence tomography (OCT), a noninvasive and cost-effective method. Retinal alterations, particularly in the retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL), have been associated with neurodegenerative and psychiatric disorders in cross-sectional OCT studies. This scoping review discusses findings on retinal changes in BD as well as their association with disease characteristics like symptom severity and illness duration and highlights OCT as a potential diagnostic tool in BD treatment.

KEY FINDINGS

The majority of studies indicate RNFL and GCL thinning in BD patients, which was found to correlate with clinical characteristics in some studies. Although the data are currently limited, there is a possibility that retinal biomarkers could facilitate monitoring of BD, but more research needs to be conducted to observe the relationship between these parameters and BD. Moreover, other factors (e.g., treatment, metabolic and inflammatory conditions) may impact retinal changes, which highlights the need for longitudinal studies to clarify these relationships. Further research should focus on replicating current findings, understanding the role of inflammation, and differentiating between retinal regions affected by BD.

Traversing the epigenetic landscape: DNA methylation from retina to brain in development and disease

DNA methylation plays a crucial role in development, aging, degeneration of various tissues and dedifferentiated cells. This review explores the multifaceted impact of DNA methylation on the retina and brain during development and pathological processes. First, we investigate the role of DNA methylation in retinal development, and then focus on retinal diseases, detailing the changes in DNA methylation patterns in diseases such as diabetic retinopathy (DR), age-related macular degeneration (AMD), and glaucoma. Since the retina is considered an extension of the brain, its unique structure allows it to exhibit similar immune response mechanisms to the brain. We further extend our exploration from the retina to the brain, examining the role of DNA methylation in brain development and its associated diseases, such as Alzheimer's disease (AD) and Huntington's disease (HD) to better understand the mechanistic links between retinal and brain diseases, and explore the possibility of communication between the visual system and the central nervous system (CNS) from an epigenetic perspective. Additionally, we discuss neurodevelopmental brain diseases, including schizophrenia (SZ), autism spectrum disorder (ASD), and intellectual disability (ID), focus on how DNA methylation affects neuronal development, synaptic plasticity, and cognitive function, providing insights into the molecular mechanisms underlying neurodevelopmental disorders.

Molecular physiology unlocks the mystery that relates cognitive impairment with the retina in schizophrenia and autism spectrum disorders: a perspective review

Schizophrenia and Autism spectrum disorders (SSD and ASD) are neurodevelopmental disorders involving cognitive impairment. Timely diagnosis is important for early intervention; currently, no tools are available to help with early diagnosis. Molecular biomarkers of cognitive impairment have been extensively studied, but clinical correlation is crucial in screening for cognitive impairment in SSD and ASD. There has been growing interest in examining the retina to scan for neurological disorders since the retina is the only part of the central nervous system that can be directly imaged non-invasively and in a timely manner. This review discusses biomarkers of cognitive impairment and their correlation to the retina in SSD and ASD. It also discusses the possible involvement of the retina and molecular biomarkers, specifically Disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) and ciliary neurotrophic factor (CNTF) in the pathophysiology of SSD and ASD. A protocol for early diagnosing cognitive impairment and its severity in SSD and ASD is also suggested. This review also mentions insights into the potential use of molecular biomarkers of cognitive impairment to enhance cognitive performance in ASD and SSD and areas where more research is needed to solve the mystery of the relationship between the retina and cognitive impairment in neurodevelopmental psychiatric disorders.

Retina in Clinical High-Risk and First-Episode Psychosis

BACKGROUND AND HYPOTHESIS

Abnormalities in the retina are observed in psychotic disorders, especially in schizophrenia.

STUDY DESIGN

Using spectral-domain optical coherence tomography, we investigated structural retinal changes in relatively metabolic risk-free youth with clinical high-risk (CHR, n = 34) and first-episode psychosis (FEP, n = 30) compared with healthy controls (HCs, n = 28).

STUDY RESULTS

Total retinal macular thickness/volume of the right eye increased in FEP (effect sizes, Cohen's d = 0.69/0.66) and CHR (d = 0.67/0.76) compared with HCs. Total retinal thickness/volume was not significantly different between FEP and CHR. Macular retinal nerve fiber layer (RNFL) thickness/volume of the left eye decreased in FEP compared with HCs (d = -0.75/-0.66). Peripapillary RNFL thickness was not different between groups. The ganglion cell (GCL), inner plexiform (IPL), and inner nuclear (INL) layers thicknesses/volumes of both eyes increased in FEP compared with HCs (d = 0.70-1.03). GCL volumes of both eyes, IPL thickness/volume of the left eye, and INL thickness/volume of both eyes increased in CHR compared with HCs (d = 0.64-1.01). In the macula, while central sector thickness/volume decreased (d = -0.62 to -0.72), superior outer (peri-foveal) sector thickness/volume of both eyes increased (d = 0.81 to 0.86) in FEP compared with HCs.

CONCLUSIONS

The current findings suggest that distinct regions and layers of the retina may be differentially impacted during the emergence and early phase of psychosis. Consequently, oculomics could play significant roles, not only as a diagnostic tool but also as a mirror reflecting neurobiological changes at axonal and cellular levels.

Multimorbidity in Severe Mental Illness as Part of the Neurodevelopmental Continuum: Physical Health-Related Endophenotypes of Schizophrenia-A Narrative Review

BACKGROUND

The majority of deaths in patients with schizophrenia and other severe mental illnesses (SMIs) are caused by natural causes, such as cardiovascular diseases (CVDs). The increased risk of CVD and other somatic diseases in SMIs cannot be fully explained by the contribution of traditional risk factors, behavioral risk factors, patients' lifestyle peculiarities, and the influence of antipsychotics. The present review has the following main objectives: (1) to aggregate evidence that neurodevelopmental disorders are the basis of SMIs; (2) to provide a review of studies that have addressed the shared genetic architecture of SMI and cardiovascular disease; and (3) to propose and substantiate the consideration of somatic diseases as independent endophenotypes of SMIs, which will make it possible to place the research of somatic diseases in SMIs within the framework of the concepts of the "neurodevelopmental continuum and gradient" and "endophenotype".

METHODS

A comprehensive literature search was performed on 1 July 2024. The search was performed using PubMed and Google Scholar databases up to June 2024.

RESULTS

The current literature reveals considerable overlap between the genetic susceptibility loci for SMIs and CVDs. We propose that somatic diseases observed in SMIs that have a shared genetic architecture with SMIs can be considered distinct physical health-related endophenotypes.

CONCLUSIONS

In this narrative review, the results of recent studies of CVDs in SMIs are summarized. Reframing schizophrenia as a multisystem disease should contribute to the activation of new research on somatic diseases in SMIs.

Genetic susceptibility to schizophrenia through neuroinflammatory pathways is associated with retinal thinning: Findings from the UK-Biobank

The human retina is part of the central nervous system and can be easily and non-invasively imaged with optical coherence tomography. While imaging the retina may provide insights on central nervous system-related disorders such as schizophrenia, a typical challenge are confounders often present in schizophrenia which may negatively impact retinal health. Here, we therefore aimed to investigate retinal changes in the context of common genetic variations conveying a risk of schizophrenia as measured by polygenic risk scores. We used population data from the UK Biobank, including White British and Irish individuals without diagnosed schizophrenia, and estimated a polygenic risk score for schizophrenia based on the newest genome-wide association study (PGC release 2022). We hypothesized that greater genetic susceptibility to schizophrenia is associated with retinal thinning, especially within the macula. To gain additional mechanistic insights, we conducted pathway-specific polygenic risk score associations analyses, focusing on gene pathways that are related to schizophrenia. Of 65484 individuals recruited, 48208 participants with available matching imaging-genetic data were included in the analysis of whom 22427 (53.48%) were female and 25781 (46.52%) were male. Our robust principal component regression results showed that polygenic risk scores for schizophrenia were associated with retinal thinning while controlling for confounding factors (b = -0.03, p = 0.007, pFWER = 0.01). Similarly, we found that polygenic risk for schizophrenia specific to neuroinflammation gene sets revealed significant associations with retinal thinning (b = -0.03, self-contained p = 0.041 (reflecting the level of association), competitive p = 0.05 (reflecting the level of enrichment)). These results go beyond previous studies suggesting a relationship between manifested schizophrenia and retinal phenotypes. They indicate that the retina is a mirror reflecting the genetic complexities of schizophrenia and that alterations observed in the retina of individuals with schizophrenia may be connected to an inherent genetic predisposition to neurodegenerative aspects of the condition. These associations also suggest the potential involvement of the neuroinflammatory pathway, with indications of genetic overlap with specific retinal phenotypes. The findings further indicate that this gene pathway in individuals with a high polygenic risk for schizophrenia could contribute through acute-phase proteins to structural changes in the retina.