From the Research
The cut-off point for Ishihara's plates in optic neuritis is typically considered to be 5 or fewer plates identified correctly out of the 9 plates used in the study by 1. Patients with optic neuritis often demonstrate color vision deficits, particularly in the red-green spectrum, which the Ishihara test is designed to detect. This threshold indicates significant color vision impairment consistent with optic nerve dysfunction. When evaluating a patient with suspected optic neuritis, the Ishihara test should be administered in proper lighting conditions, with each plate shown for approximately 3 seconds. The pattern of errors is also important, as optic neuritis typically causes a generalized dyschromatopsia rather than specific color axis deficiencies. This color vision deficit often precedes visual acuity loss and may persist even after visual acuity improves during recovery. The test is particularly useful when combined with other clinical findings such as reduced visual acuity, afferent pupillary defect, visual field defects, and pain with eye movement to establish the diagnosis of optic neuritis. Some studies, such as 2, suggest that the Hardy-Rand-Rittler 4th edition test may be more sensitive than the Ishihara test in detecting color vision defects in patients with optic neuropathy. However, the Ishihara test remains a widely used and useful tool in the diagnosis of optic neuritis, as shown in studies such as 3 and 1. It is essential to consider the results of the Ishihara test in the context of other clinical findings and to use the test as part of a comprehensive evaluation of the patient. In terms of treatment, studies such as 4 and 5 have investigated the use of corticosteroids in the treatment of optic neuritis, but the focus of the current question is on the diagnostic use of Ishihara's plates. Key points to consider when using the Ishihara test in the diagnosis of optic neuritis include:
- The test should be administered in proper lighting conditions
- Each plate should be shown for approximately 3 seconds
- The pattern of errors is important, as optic neuritis typically causes a generalized dyschromatopsia
- The test is particularly useful when combined with other clinical findings
- The results of the test should be considered in the context of other clinical findings and as part of a comprehensive evaluation of the patient.