Subclinical dysthyroid optic neuropathy: tritan deficiency as an early sign of dysthyroid optic neuropathy.

PURPOSE: The aim of this research was to investigate the subclinical findings of dysthyroid optic neuropathy (DON) and to look for early indicators for optic nerve compression in patients with Graves' orbitopathy. PATIENTS AND METHODS: In this observational, retrospective study, the medical charts of 24 patients (32 eyes) with a diagnosis of DON between 2008 and 2019 were included. Our goal was to identify potential pathological signs in patients with DON prior to the definitive diagnosis of DON. RESULTS: We discovered that the earliest pathological sign in the subclinical cases was tritan deficiency obtained with a standardised colour vision test by Arden. In all cases but one, regardless of the visual field (VF) defects, the tritan values were pathological (based on a threshold of ≥8%) in the subclinical phase. The mean tritan value was 19.12% (range 6.9-80.8%) at the time of the subclinical phase and 32.16% (range 6.3-100.0%) at the time of the diagnosis of DON. The sensitivity of the colour vision test was 20% for protan and 96.67% for tritan in the subclinical phase. At the time of the definitive diagnosis of DON, the sensitivity of protan was 48.15% compared to 96.30% for tritan. CONCLUSION: We found that changes in vision affecting the blue-yellow (tritan) colours resulting from the compression of optic nerve, even in affected patients with normal VF tests, are a reliable early sign of DON.