Contrast Sensitivity and Visual-Field Thresholds in Patients with Thyroid Optic Neuropathy

Thyroid optic neuropathy is one of the most troubling complications of endocrine ophthalmopathies. It is related to the degree of extraocular muscle swelling in the apex of the orbit. The purpose of this study was to investigate contrast sensitivity and visual-field thresholds in patients with thyroid optic neuropathy. We examined twenty-two patients aged 29 – 63 years (mean 45.3 years). The control group consisted of fifteen healthy persons of similar age. Contrast sensitivity was measured by means of Volkov's charts (sinusoidal gratings) at eight spatial frequencies from 17.5 to 0.46 cycles deg⁻¹. The visual field was investigated with a static automatic perimeter (Allgan Humphrey Field Analyzer) by means of the central 30-2 threshold test. All patients underwent a complete ophthalmological examination including best corrected Snellen visual acuity, fundus copy, and proptosis measurement with the Hertel exophthalmometer. The mean proptosis of patients was 19.4 mm. Fifteen of the patients had decreased visual acuity. Contrast sensitivity at low spatial frequencies was significantly reduced in the patients. It was established that a reduction of visual-field threshold accompanies the decrease of visual acuity. Our results show that contrast sensitivity and visual-field threshold testing are very sensitive at detecting early optic neuropathy and may be a useful means of following patients after treatment.