Walsh & Hoyt: Differentiation by Physical Examination

Visual acuity is nearly always impaired in macular disease and often in optic neuropathies. The issue often comes to the extent of loss of vision in comparison to the three common measures of optic nerve function. This optic nerve triad consists of the relative afferent pupillary defect (APD), color vision and brightness sense. An APD is seen when the consensual pupillary response is greater than the direct pupillary response. This is noted qualitatively, or it can be quantitated with the use of neutral density filters. Color vision is best assessed with a Farnsworth-Munsell 100-hue (FM-100) test. However, shorter and more convenient tests are often performed, such as the D-15 which is the desaturated form of the FM-100, or the use of pseudoisochromatic plates of the A-O or Ishihara type. A third sensitive measure of optic nerve function is noting the change in brightness sense.