Comparison of Ishihara and Hardy-Rand-Rittler Pseudoisochromatic Plates in Non-Arteritic Anterior Ischaemic Optic Neuropathy

Abstract

Pseudoisochromatic plates, such as Ishihara and Hardy-Rand-Rittler (HRR) tests, are designed as screening tools to test colour vision defects. The tests are often designed to detect congenital red-green colour blindness and their measurement properties for acquired optic neuropathies are not known. The aim of this study is to determine the sensitivity and specificity of Ishihara and HRR pseudoisochromatic plates in detecting dyschromatopsia in patients with unilateral non-arteritic anterior ischaemic optic neuropathy. Nineteen such patients were tested using Ishihara and the HRR plates in the affected and the unaffected (control) eye. The results were correlated to that on an anomaloscope (Oculus HMC Anomaloskop MR®). Mild deuteranomaly was the dyschromatopsia detected by an anomaloscope in the affected eye of the patients. The sensitivity and specificity of the Ishihara test in the affected eyes are 75% and 40%, respectively. The sensitivity and specificity of the HRR test in eyes affected with non-arteritic anterior ischaemic optic neuropathy are 100% and 20%, respectively. It is concluded that the anomaloscope that was considered the “gold standard” has several limitations and may not detect all acquired dyschromatopia. On the other hand, whilst it is correct that pseudoisochromatic plates are screening tests and the results must be correlated with other optic nerve functions, the HRR test has a higher sensitivity and specificity than Ishihara colour plates in detecting dyschromatopsia in non-arteritic anterior ischaemic optic neuropathy eyes.