Optic neuritis is an important cause of acute or subacute visual loss. In clinical practice, optic neuritis must often be distinguished from other optic neuropathies, retinal diseases, anterior-segment or ocular media disorders, non-organic visual loss, and other mimics. The 2022 International Criteria for Optic Neuritis were developed to standardize the diagnosis of optic neuritis, but their performance in Chinese clinical settings, where aquaporin-4 immunoglobulin G-positive and myelin oligodendrocyte glycoprotein immunoglobulin G-positive optic neuritis are relatively common, remains uncertain.

This multicenter prospective observational study is enrolling patients with acute or subacute visual loss in whom optic neuritis is included in the differential diagnosis. The study is designed to evaluate the diagnostic performance of the 2022 International Criteria for Optic Neuritis alone and with an antibody-stratified adjunct. The index classifications will be compared with an expert-adjudicated reference-standard diagnosis. No experimental treatment is assigned by the study. All diagnostic tests and treatments are determined by the treating clinicians according to routine clinical care. Study data are collected using a structured protocol-defined case report form.

This is a multicenter prospective observational diagnostic accuracy study conducted in China. Structured prospective electronic case report form-based data collection for the primary diagnostic accuracy cohort began on January 6, 2025. The study population includes individuals with a new acute or subacute episode of visual loss or optic nerve-related visual dysfunction in one or both eyes, for whom optic neuritis is included in the initial differential diagnosis at participating clinical centers. Each participant contributes only one clinical episode to the primary diagnostic accuracy cohort.

The main objective is to evaluate the diagnostic performance of the 2022 International Criteria for Optic Neuritis in a real-world Chinese clinical setting. The study is also designed to evaluate the 2022 International Criteria for Optic Neuritis with a prespecified antibody-stratified adjunct strategy designed for settings where aquaporin-4 immunoglobulin G-positive optic neuritis and myelin oligodendrocyte glycoprotein immunoglobulin G-positive optic neuritis are relatively common and antibody testing is clinically available.

Baseline clinical data are collected prospectively using a structured electronic case report form. The form captures demographic information, symptom onset, laterality, pain with eye movement, visual acuity, protocol-defined color vision assessment, relative afferent pupillary defect assessment, and other predefined clinical variables.

Paraclinical data are collected when obtained as part of routine clinical care. These data may include visual field testing, optical coherence tomography, orbital or optic nerve MRI, serum aquaporin-4 immunoglobulin G, serum myelin oligodendrocyte glycoprotein immunoglobulin G, and other laboratory or imaging results. Optical coherence tomography is encouraged for objective structural characterization when clinically feasible, but it is not mandated by study participation. Follow-up optical coherence tomography at 3 to 6 months is encouraged when clinically feasible. Available follow-up optical coherence tomography data will be summarized descriptively. Exploratory optical coherence tomography-available analyses may be performed if data are sufficient; these analyses are not required for the primary diagnostic accuracy analysis. MRI and antibody testing are performed when considered clinically appropriate by the treating clinical team.

The 2022 International Criteria for Optic Neuritis serve as the index test. Index-test classifications will be assigned using baseline clinical data and paraclinical data eligible for application of the 2022 International Criteria for Optic Neuritis that were obtained within 3 months after symptom onset for the current clinical episode, based on the timing of the examination or sample collection. Follow-up information obtained after this diagnostic window will not be used to revise the index-test classification. Participants will be classified as definite optic neuritis, possible optic neuritis, or not optic neuritis according to prespecified rules. A prespecified antibody-stratified adjunct strategy, based on our published adjunct framework, will then be applied in combination with the 2022 International Criteria for Optic Neuritis, rather than as a standalone diagnostic test. This adjunct strategy incorporates aquaporin-4 immunoglobulin G seropositivity and clear-positive myelin oligodendrocyte glycoprotein immunoglobulin G results together with objective optic nerve evidence. The detailed operational rules are specified in the study protocol and are based on the cited published framework.

Participants are followed for up to 6 months after enrollment whenever feasible. Follow-up information includes available information on subsequent clinical course, repeat ophthalmic assessments, additional imaging or laboratory results, treatment response, and alternative diagnoses made during routine clinical care. This follow-up information will be used to support the expert-adjudicated reference-standard diagnosis. Participants for whom the reference-standard adjudication committee cannot assign a diagnosis of optic neuritis or non-optic neuritis because of insufficient clinical, imaging, laboratory, or follow-up information will be classified as indeterminate according to prespecified adjudication rules. Indeterminate reference-standard cases will be summarized separately and excluded from the primary binary diagnostic accuracy analysis.

Follow-up information beyond the prespecified index-test diagnostic window will be used for reference-standard adjudication only.

The reference-standard diagnosis will be determined by an expert adjudication panel. Two expert adjudicators will independently review the structured baseline clinical form and all available ophthalmic, imaging, laboratory, treatment, and follow-up information according to a prespecified adjudication process. The adjudicators will be masked to the 2022 International Criteria for Optic Neuritis classification and the antibody-stratified adjunct classification. They will not be masked to the source clinical, ophthalmic, imaging, laboratory, treatment, or follow-up information required for reference-standard adjudication. Disagreements will be resolved by a third expert adjudicator. Participants will be classified as optic neuritis, non-optic neuritis, or indeterminate. Cases with an indeterminate reference-standard diagnosis will be reported separately and will not be included in the primary diagnostic accuracy analysis. The initial agreement between the two expert adjudicators will be summarized using the percentage agreement and Cohen's kappa for the three-category reference-standard classification of optic neuritis, non-optic neuritis, or indeterminate.

The primary diagnostic accuracy analysis will compare the index-test classification with the expert-adjudicated reference-standard diagnosis. In the main analysis, definite optic neuritis will be classified as index-test positive and not optic neuritis will be classified as index-test negative. Possible optic neuritis will be treated as an indeterminate index-test category, excluded from the main binary diagnostic accuracy analysis, and reported separately. Key secondary analyses will evaluate the diagnostic yield of definite optic neuritis, the distribution of possible optic neuritis, the performance of a low-threshold definition that classifies definite or possible optic neuritis as index-test positive, and the performance of the 2022 International Criteria for Optic Neuritis with the antibody-stratified adjunct. Diagnostic measures will include sensitivity, specificity, positive predictive value, negative predictive value, likelihood ratios, and 95 percent confidence intervals, as appropriate.

The study is observational. The investigators do not assign experimental treatment or alter routine clinical management. Treatment decisions, including corticosteroids, plasma exchange, immunosuppressive therapy, biologic therapy, or treatment for non-inflammatory alternative diagnoses, are made by the treating clinical team as part of routine clinical care and are not dictated by the study protocol.

At the time this record was initially submitted for public registration, recruitment was ongoing, and database lock, formal reference-standard adjudication, final index-test classification, and the primary diagnostic accuracy analysis had not occurred.

Inclusion Criteria:

1. Individuals presenting with a new acute or subacute episode of visual loss or optic nerve-related visual dysfunction in one or both eyes, for whom optic neuritis is considered a reasonable differential diagnosis by the treating clinical team at the initial clinical assessment and before final diagnostic adjudication.
2. Symptom onset of the current episode within 90 days before enrollment.

Exclusion Criteria:

1. The participant has previously been enrolled in this study. Each participant may be enrolled only once.

A history of optic neuritis or recurrent optic neuropathy before the current episode is not an exclusion criterion.

Individuals with a new acute or subacute episode of visual loss or optic nerve-related visual dysfunction in one or both eyes, for whom optic neuritis is included in the initial differential diagnosis at participating clinical centers. Each participant contributes only one clinical episode to the primary diagnostic accuracy cohort.

De-identified participant-level data and a data dictionary will be made available to qualified researchers upon reasonable request after publication of the main diagnostic accuracy results, subject to ethics approval, institutional approval, and execution of a data use agreement.