Effect of Induced Refractive Error and Nuclear Sclerotic Cataracts on Ishihara Colour Plate Testing

Objective: To determine the effect of induced refractive blur and nuclear sclerotic (NS) cataracts on Ishihara colour plate (ICP) scores. Design: Prospective evaluation of a diagnostic test Participants: Patients who presented to Hotel Dieu Hospital Eye clinic between January and March 2010 with either a lone diagnosis of nuclear sclerotic cataracts, or with no identified ocular disease with complete examination. Methods: Patients were divided into two groups: those having no identified ocular disease on examination, and those with a lone diagnosis of NS cataracts. The first group was refractively blurred with +3D, +6D, +9D and +12D lenses. Best corrected visual acuity (BCVA) at near and ICP scores was obtained from both groups. Results: There were 20 patients in each group. BCVA at near and ICP values declined with increasing amounts of plus lenses as expected. With the application of the +3D, +6D, +9D, and +12D lenses, the association between ICP scores and BCVA at near decreased (-0.845, -0.678, -0.374, and -0.363 respectively). There was little clinical decline in absolute ICP scores until lenses of +9D (mean BCVA at near = 20/400) or greater were applied. The correlation between ICP scores and BCVA at near declines due to NS cataracts was -0.53. Conclusion: ICP testing is valid to BCVA at near of 20/100 when the acuity decline is due solely to NS cataracts. Further study is required to determine whether or not severe vision loss due to NS cataracts affects ICP scores and at what visual acuity.