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Case Report

Invalidation of the Farnsworth D15 Test in Dichromacy Secondary to Practice

Ng, Jason S., OD, PhD, FAAO*; Morton, Warren A., BS

doi: 10.1097/OPX.0000000000001184

SIGNIFICANCE The Farnsworth D15 test can be subverted by patients even with severe red-green color deficiency.

PURPOSE To describe a case showing that perfect performance on the Farnsworth D15 is possible after practicing the test.

CASE REPORT A 23-year-old man presented for a comprehensive color vision evaluation. He had only minor complaints with regard to color vision and otherwise normal vision and ocular health. Based on anomaloscope findings, he was diagnosed with protanopia, a form of dichromacy in which the patient does not have any functional L cones, only S and M cones. The patient practiced the Farnsworth D15 test and returned for a follow-up visit in which he performed the test perfectly four times (i.e., twice in the regular order and twice using cap 15 as the pilot cap). In addition, the patient returned a year later and again performed the test perfectly, indicating long-term learning.

CONCLUSIONS All studies to date have shown that patients with dichromacy fail the Farnsworth D15 test. This case report shows that it is indeed possible for highly motivated patients to subvert the test through practice, and knowledge of this possibility is very important, especially in occupational testing.

Southern California College of Optometry at Marshall B. Ketchum University, Fullerton, California (all authors) *

Submitted: August 15, 2017

Accepted: November 24, 2017

Funding/Support: None of the authors have reported funding/support.

Conflict of Interest Disclosure: None of the authors have reported a financial conflict of interest.

Author Contributions and Acknowledgments: Conceptualization: JSN; Data Curation: JSN; Formal Analysis: JSN; Investigation: JSN, WAM; Methodology: JSN; Project Administration: JSN; Resources; Writing – Original Draft: JSN, WAM; Writing – Review & Editing: JSN, WAM.

The authors thank Dr. Béla Török for allowing the authors to use the D15 plots generated from his Web site for use in this article.

© 2018 American Academy of Optometry