Could structural changes in the retinal layers be a new biomarker of mental disorders? A systematic review and thematic synthesis

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

INTRODUCTION

Abnormal findings on optical coherence tomography (OCT) and electroretinography (ERG) have been reported in participants with schizophrenia spectrum disorders (SSDs). This study aims to reveal the pooled standard mean difference (SMD) in retinal parameters on OCT and ERG among participants with SSDs and healthy controls and their association with demographic characteristics, clinical symptoms, smoking, diabetes mellitus, and hypertension.

METHODS

Using PubMed, Scopus, Web of Science, and PSYNDEX, we searched the literature from inception to March 31, 2023, using specific search terms. This study was registered with PROSPERO (CRD4202235795) and conducted according to PRISMA 2020.

RESULTS

We included 65 studies in the systematic review and 44 in the meta-analysis. Participants with SSDs showed thinning of the peripapillary retinal nerve fiber layer (pRNFL), macular ganglion cell layer- inner plexiform cell layer, and retinal thickness in all other segments of the macula. A meta-analysis of studies that excluded SSD participants with diabetes and hypertension showed no change in results, except for pRNFL inferior and nasal thickness. Furthermore, a significant difference was found in the pooled SMD of pRNFL temporal thickness between the left and right eyes. Meta-regression analysis revealed an association between retinal thinning and duration of illness, positive and negative symptoms. In OCT angiography, no differences were found in the foveal avascular zone and superficial layer foveal vessel density between SSD participants and controls. In flash ERG, the meta-analysis showed reduced amplitude of both a- and b-waves under photopic and scotopic conditions in SSD participants. Furthermore, the latency of photopic a-wave was significantly shorter in SSD participants in comparison with HCs.

DISCUSSION

Considering the prior report of retinal thinning in unaffected first-degree relatives and the results of the meta-analysis, the findings suggest that retinal changes in SSDs have both trait and state aspects. Future longitudinal multimodal retinal imaging studies are needed to clarify the pathophysiological mechanisms of these changes and to clarify their utility in individual patient monitoring efforts.

Retinal layers and associated clinical factors in schizophrenia spectrum disorders: a systematic review and meta-analysis

INTRODUCTION

The retina shares structural and functional similarities with the brain. Furthermore, structural changes in the retina have been observed in patients with schizophrenia spectrum disorders (SSDs). This systematic review and meta-analysis investigated retinal abnormalities and their association with clinical factors for SSD.

METHODS

Studies related to retinal layers in SSD patients were retrieved from PubMed, Scopus, Web of Science, Cochrane Controlled Register of Trials, International Clinical Trials Registry Platform, and PSYNDEX databases from inception to March 31, 2021. We screened and assessed the eligibility of the identified studies. EZR ver.1.54 and the metafor package in R were used for the meta-analysis and a random-effects or fixed-effects model was used to report standardized mean differences (SMDs).

RESULTS

Twenty-three studies (2079 eyes of patients and 1571 eyes of controls) were included in the systematic review and meta-analysis. The average peripapillary retinal nerve fiber layer (pRNFL) thickness, average macular thickness (MT), and macular ganglion cell layer-inner plexiform layer (GCL-IPL) thickness were significantly lower in patients than in controls (n = 14, 6, and 3, respectively; SMD = -0.33, -0.49, and -0.43, respectively). Patients also had significantly reduced macular volume (MV) compared to controls (n = 7; SMD = -0.53). The optic cup volume (OCV) was significantly larger in patients than in controls (n = 3; SMD = 0.28). The meta-regression analysis indicated an association between several clinical factors, such as duration of illness and the effect size of the pRNFL, macular GCL-IPL, MT, and MV.

CONCLUSION

Thinning of the pRNFL, macular GCL-IPL, MT, and MV and enlargement of the OCV in SSD were observed. Retinal abnormalities may be applicable as state/trait markers in SSDs. The accumulated evidence was mainly cross-sectional and requires verification by longitudinal studies to characterize the relationship between OCT findings and clinical factors.

Enhanced medical diagnosis for dOCTors: a perspective of optical coherence tomography

SIGNIFICANCE

After three decades, more than 75,000 publications, tens of companies being involved in its commercialization, and a global market perspective of about USD 1.5 billion in 2023, optical coherence tomography (OCT) has become one of the fastest successfully translated imaging techniques with substantial clinical and economic impacts and acceptance.

AIM

Our perspective focuses on disruptive forward-looking innovations and key technologies to further boost OCT performance and therefore enable significantly enhanced medical diagnosis.

APPROACH

A comprehensive review of state-of-the-art accomplishments in OCT has been performed.

RESULTS

The most disruptive future OCT innovations include imaging resolution and speed (single-beam raster scanning versus parallelization) improvement, new implementations for dual modality or even multimodality systems, and using endogenous or exogenous contrast in these hybrid OCT systems targeting molecular and metabolic imaging. Aside from OCT angiography, no other functional or contrast enhancing OCT extension has accomplished comparable clinical and commercial impacts. Some more recently developed extensions, e.g., optical coherence elastography, dynamic contrast OCT, optoretinography, and artificial intelligence enhanced OCT are also considered with high potential for the future. In addition, OCT miniaturization for portable, compact, handheld, and/or cost-effective capsule-based OCT applications, home-OCT, and self-OCT systems based on micro-optic assemblies or photonic integrated circuits will revolutionize new applications and availability in the near future. Finally, clinical translation of OCT including medical device regulatory challenges will continue to be absolutely essential.

CONCLUSIONS

With its exquisite non-invasive, micrometer resolution depth sectioning capability, OCT has especially revolutionized ophthalmic diagnosis and hence is the fastest adopted imaging technology in the history of ophthalmology. Nonetheless, OCT has not been completely exploited and has substantial growth potential-in academics as well as in industry. This applies not only to the ophthalmic application field, but also especially to the original motivation of OCT to enable optical biopsy, i.e., the in situ imaging of tissue microstructure with a resolution approaching that of histology but without the need for tissue excision.

Abberant inverted U-shaped brain pattern and trait-related retinal impairment in schizophrenia patients with combined auditory and visual hallucinations: a pilot study

Schizophrenic patients often experience auditory hallucinations (AHs) and visual hallucinations (VHs). However, brain and retinal alterations associated with combined AHs and VHs in schizophrenic patients are unknown. This study aimed o investigate brain and retinal alterations in first episode un-treated schizophrenic patients with combined AHs and VHs (FUSCHAV). FUSCHAV patients (n = 120), divided into four groups according to severity of AH and VH symptoms, were compared to healthy controls (n = 30). Gray matter volume (GMV) and global functional connectivity density (gFCD) were recorded to reflect brain structure and functional alterations. Total retinal thickness was acquired by optical coherence tomography to assess retinal impairment. The majority of FUSCHAV patients (85.8%) demonstrated both GMV reduction and gFCD increases along with retinal thinning compared to healthy controls. The severity of GMV reduction and gFCD increase differed between patient groups, ranked from highest to lowest severity as follows: severe AHs combined with severe VHs (FUSCHSASV, 20 patients), moderate AHs combined with severe VHs (FUSCHMASV, 23 patients), severe AHs combined with moderate VHs (FUSCHSAMV, 28 patients), and moderate AHs combined with moderate VHs (FUSCHMAMV, 26). Retinal impairment was similar among the four FUSCHAV groups. GMV reduction and gFCD increases in the frontal-parietal lobule show an inverted U-shaped pattern among FUSCHAV patients according to AH and VH severity, while retinal impairment remains stable among FUSCHAV groups. These findings indicate a reciprocal deterioration in auditory and visual disturbances among FUSCHAV patients.

Antipsychotic agents deteriorate brain and retinal function in schizophrenia patients with combined auditory and visual hallucinations: A pilot study and secondary follow-up study

INTRODUCTION

Schizophrenia patients often experience auditory hallucinations (AHs) and visual hallucinations (VHs). However, the degree and type of brain and retinal alterations associated with combined AHs and VHs in schizophrenia patients remain unknown. There is an urgent need for a study that investigates the trajectory of brain and retinal alterations in patients with first-episode untreated schizophrenia accompanied by combined AHs and VHs (FUSCHAV).

METHODS

FUSCHAV patients (n = 120), divided into four groups according to AH and VH symptom severity (severe AHs combined with severe VHs [FUSCHSASV, 20 patients]; middle-to-moderate AHs combined with severe VHs [FUSCHMASV, 23 patients]; severe AHs combined with middle-to-moderate VHs [FUSCHSAMV, 28 patients]; and middle-to-moderate AHs combined with middle-to-moderate VHs [FUSCHMAMV, 26 patients]), were compared to healthy controls (n = 30). Gray matter volume (GMV) was adopted for brain structural alteration assessment. Total retinal thickness was adopted as a measure of retinal thickness impairment.

RESULTS

In the pilot study, the rate of GMV reduction showed an inverted U-shaped pattern across the different FUSCHAV patient groups according to AH and VH severity. The degree of retinal impairment remained stable across the groups. More notably, in the secondary follow-up study, we observed that, after 6 months of treatment with antipsychotic agents, all the GMV reduction-related differences across the different patient groups disappeared, and both GMV and retinal thickness demonstrated a tendency to deteriorate.

CONCLUSIONS

These findings indicate the need for heightened alertness on brain and retinal impairments in patients with FUSCHAV. Further deteriorations induced by antipsychotic agent treatment should be monitored in clinical practice.

Schizophrenia and the retina: Towards a 2020 perspective

BACKGROUND

Differences between people with schizophrenia and psychiatrically healthy controls have been consistently demonstrated on measures of retinal function such as electroretinography (ERG), and measures of retinal structure such as optical coherence tomography (OCT). Since our 2015 review of this literature, multiple new studies have been published using these techniques. At the same time, the accumulation of data has highlighted the "fault lines" in these fields, suggesting methodological considerations that need greater attention in future studies.

METHODS

We reviewed studies of ERG and OCT in schizophrenia, as well as data from studies whose findings are relevant to interpreting these papers, such as those on effects of the following on ERG and OCT data: comorbid medical conditions that are over-represented in schizophrenia, smoking, antipsychotic medication, substance abuse, sex and gender, obesity, attention, motivation, and influences of brain activity on retinal function.

RESULTS

Recent ERG and OCT studies continue to support the hypothesis of retinal structural and functional abnormalities in schizophrenia, and suggest that these are relevant to understanding broader aspects of pathophysiology, neurodevelopment, and neurodegeneration in this disorder. However, there are differences in findings which suggest that the effects of multiple variables on ERG and OCT data need further clarification.

CONCLUSIONS

The retina, as the only component of the CNS that can be imaged directly in live humans, has potential to clarify important aspects of schizophrenia. With greater attention to specific methodological issues, the true potential of ERG and OCT as biomarkers for important clinical phenomena in schizophrenia should become apparent.