Looking ahead: electroretinographic anomalies, glycogen synthase kinase-3, and biomarkers for neuropsychiatric disorders

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.

Optical Coherence Tomography Findings in Bipolar Disorder Patients and the Related Factors

Background

This study's purpose is to determine the effects of current episode and the mood stabilizers on chorioretinal layer thicknesses of bipolar disorder (BD) patients using spectral-domain optical coherence tomography (SD-OCT).

Methods

Sixty-seven patients were diagnosed with BD I and using lithium (Li) or valproic acid (VPA), of whom 20 were manic, 24 were depressive, and 23 were in remission, and 49 healthy individuals were included in the study. Peripapillary retinal nerve fiber layer (RNFL), ganglion cell layer, and macular thicknesses of the participants were measured automatically using SD-OCT, and their choroid layer thicknesses were measured manually using the depth imaging mode of SD-OCT. Statistical analysis of the data was performed using Statistical Package for the Social Sciences version 23.0.

Results

The patient group's mean age was 39.78 ± 11.78, and the control group's mean age was 42.06 ± 12.10. The mean disease duration was 13.22 ± 8.23 in the patient group, and 26 patients were using Li. While peripapillary RNFL thicknesses were lower in the patient group (P < .05), other layer measurements were similar between the groups. Moreover, the episodes experienced by BD patients did not affect chorioretinal SD-OCT measurements. The patients on VPA had significantly lower RNFL thicknesses compared to the control and the Li groups, and all chorioretinal measurements were similar between the Li and the control groups.

Conclusion

As a result of the study, it was established that neurodegenerative processes play a role in the pathophysiology of BD and the usage of Li is protective against the neurodegeneration of RNFL. Retinal changes measured with SD-OCT can be used for the diagnosis and prognosis of BD and for evaluating responses to mood stabilizers.

Subsequent and simultaneous electrophysiological investigation of the retina and the visual cortex in neurodegenerative and psychiatric diseases: what are the forecasts for the medicine of tomorrow?

Visual electrophysiological deficits have been reported in neurodegenerative disorders as well as in mental disorders. Such alterations have been mentioned in both the retina and the cortex, notably affecting the photoreceptors, retinal ganglion cells (RGCs) and the primary visual cortex. Interestingly, such impairments emphasize the functional role of the visual system. For this purpose, the present study reviews the existing literature with the aim of identifying key alterations in electroretinograms (ERGs) and visual evoked potentials electroencephalograms (VEP-EEGs) of subjects with neurodegenerative and psychiatric disorders. We focused on psychiatric and neurodegenerative diseases due to similarities in their neuropathophysiological mechanisms. Our research focuses on decoupled and coupled ERG/VEP-EEG results obtained with black-and-white checkerboards or low-level visual stimuli. A decoupled approach means recording first the ERG, then the VEP-EEG in the same subject with the same visual stimuli. The second method means recording both ERG and VEP-EEG simultaneously in the same participant with the same visual stimuli. Both coupled and decoupled results were found, indicating deficits mainly in the N95 ERG wave and the P100 VEP-EEG wave in Parkinson’s, Alzheimer’s, and major depressive disorder. Such results reinforce the link between the retina and the visual cortex for the diagnosis of psychiatric and neurodegenerative diseases. With that in mind, medical devices using coupled ERG/VEP-EEG measurements are being developed in order to further investigate the relationship between the retina and the visual cortex. These new techniques outline future challenges in mental health and the use of machine learning for the diagnosis of mental disorders, which would be a crucial step toward precision psychiatry.

VISUAL FUNCTION AND RETINAL CHANGES IN PATIENTS WITH BIPOLAR DISORDER

PURPOSE

To evaluate visual and retinal changes in patients with bipolar disorder. To analyze the correlation between structural changes and visual function parameters.

METHODS

Thirty patients with bipolar disorder and 80 healthy controls underwent visual function evaluation with Early Treatment Diabetic Retinopathy Study charts at 100%, 2.50%, and 1.25% contrast, Pelli-Robson chart, and color vision Farnsworth and Lanthony tests. Analysis of the different retinal layers was performed using Spectralis optical coherence tomography with automated segmentation software. Correlation analysis between structural and functional parameters was conducted.

RESULTS

Patients with bipolar disorder presented worse color vision compared with controls (Lanthony's index, P = 0.002). Full macular thickness, the retinal nerve fiber layer (RNFL), ganglion cell layer, and inner plexiform layer were reduced in patients compared with healthy individuals (P < 0.005). The inner nuclear layer was significantly thickened in patients (P < 0.005). Peripapillary RNFL thickness was reduced in all temporal sectors (P < 0.005). Significant correlations were found between visual acuity and the RNFL thickness, the Pelli-Robson score and the inner plexiform layer, and between the Lanthony's color index and the ganglion cell layer thickness.

CONCLUSION

Patients with bipolar disorder present quantifiable thinning of the macular RNFL, ganglion cell layer, and inner plexiform layer, as well as in the peripapillary RNFL thickness, and increasing thinning in the inner nuclear layer.