Farnsworth D-15: How to Use It and What It Detects

por Good-Lite Co 15 de julio de 2026

por Good-Lite Co Publicado en 15 de julio de 2026Actualizado en 15 de julio de 2026

What Is the Farnsworth D-15 Test?

The Farnsworth D-15, also known as the Panel D-15 or Dichotomous Test for Color Blindness, was developed in 1947 by Dean Farnsworth of the U.S. Navy. The term "dichotomous" defines its purpose: the test separates patients into exactly two groups, those with strong-to-moderate color vision deficiency (CVD) and those who are mildly deficient or color normal.

The Ishihara tells you if a patient has red-green color deficiency. The D-15 tells you what kind, how severe, and whether it is progressing. Unlike Ishihara plates, the D-15 detects all three axes of color deficiency: protan (red weakness), deutan (green weakness), and tritan (blue-yellow weakness). Ishihara cannot identify tritan defects at all.

Compared to the Farnsworth-Munsell 100 Hue Test, the D-15 is a simplified, faster subset designed for rapid clinical classification rather than in-depth defect mapping. It holds FDA and U.S. Defense Personnel Support Center approval for clinical and military use. With roughly 300 million people affected by CVD worldwide, and prevalence rates reaching 8% of males and 0.5% of females of Northern European descent, reliable classification tools like the D-15 are essential.

Who Should Be Tested and Why It Matters Clinically

Eight percent of your male patients may have unclassified color vision deficiency. A 2025 meta-analysis published in Ophthalmology (AAO Journal), drawing from 1,703,619 participants across 56 studies, found global pediatric CVD prevalence of 4.38% in males. These numbers make a strong case for routine classification beyond basic Ishihara screening.

The D-15 serves three primary patient populations. First, patients with suspected congenital red-green or tritan deficiency who need classification beyond a simple pass/fail screening. Second, patients on medications with known ocular toxicity, including ethambutol, hydroxychloroquine, and sildenafil, where color vision changes can signal drug-related damage. Third, patients with progressive retinal or optic nerve disease who require serial monitoring.

The D-15's value for acquired CVD deserves special emphasis. Unlike congenital screening tools, it can track changes over time, which is critical for ophthalmologists managing retinal or neuro-ophthalmic disease. In a vision rehabilitation clinic study, 65.1% of patients with CVD had retinal disease and 30.2% had optic nerve disease as the primary cause.

For occupational screening, the D-15 remains highly relevant for electricians, military ground roles, police, firefighters, and signal workers. As of January 2025, the FAA no longer accepts the D-15 (or Ishihara plates) for unrestricted pilot medical certification, shifting to computer-based tests for new applicants. The D-15 continues to serve non-aviation occupational contexts and clinical diagnosis.

There is also a practical billing advantage: the D-15 qualifies as an extended color vision test, providing greater reimbursement than basic pseudoisochromatic plate screening. This makes clinical and financial sense for practices that invest in thorough color vision evaluation.

Test Components and Setup

The Farnsworth D-15 kit consists of one fixed reference cap labeled "0" and 15 numbered colored caps (1 through 15). Together, these caps form an incomplete color circle spanning the full hue spectrum. Each cap contains a Munsell color sample mounted under a clear cover.

The patient should be seated at a working distance of 19.5 inches (50 cm), with the caps arranged on a black background. Proper illumination is non-negotiable: the test must be conducted under CIE Illuminant C or D65 conditions, approximately 6500K daylight. Improper lighting is one of the leading causes of inaccurate results in real-world clinical settings and is an avoidable error.

When monitoring acquired disease, test monocularly to detect asymmetric defects between eyes. This is especially important for patients on medications with ocular toxicity or those with unilateral optic nerve pathology.

Administration takes roughly four to five times less time than the FM 100 Hue Test, making the D-15 practical for routine clinical use. Caps should be stored away from direct light and replaced periodically, as fading compromises test validity and worn caps can produce misleading results.

Step-by-Step Administration Method

Step 1: Seat the patient at the correct working distance (50 cm) under standardized daylight illumination (CIE D65, ~6500K). Verify your light source before beginning.

Step 2: Scramble the 15 caps and place them randomly in front of the patient alongside the fixed reference cap "0."

Step 3: Instruct the patient to select the cap most similar in color to the reference cap, then continue arranging the remaining caps in chromatic sequence, placing each next to the last one chosen.

Step 4: Once the patient has completed the arrangement, flip the caps over and record the sequence by number on the score sheet (e.g., 0-1-2-3-4... for a perfect arrangement, or a disordered sequence for a patient with CVD).

Step 5: Draw connecting lines between consecutive caps in the patient's chosen order on the circular score sheet. The pattern of these lines reveals the type and severity of any defect.

The test should be administered without time pressure. Most patients complete it in under five minutes. When monitoring acquired or progressive CVD, always test each eye separately and document results for comparison over time.

Scoring and Interpreting Results

The D-15 score sheet plots the 15 cap positions on a circular diagram. After recording the patient's arrangement, you draw connecting lines between consecutive caps in the order the patient chose. A color-normal patient produces lines that follow the outer edge of the circle in orderly sequence. A patient with significant CVD produces lines that cut across the circle.

The critical scoring concept is the crossing error: any line that crosses the center of the circle (a diametrical crossing) represents a significant transposition. Two or more major diametrical crossing errors constitute a failed test, indicating clinically significant color vision deficiency.

The direction of crossing lines identifies the defect type. Crossings parallel to the protan axis indicate protanopia or protanomaly (red weakness). Crossings parallel to the deutan axis indicate deuteranopia or deuteranomaly (green weakness). Crossings parallel to the tritan axis indicate tritanopia (blue-yellow weakness). This axis-specific classification is what makes the D-15 diagnostically superior to simple pass/fail screening tools.

A 2021 study in Color Research & Application by Evans, Rodriguez-Carmona, and Barbur validated significant correlations between the number of crossings and Color Difference Vector (CDV) quantitative parameters, confirming that the traditional crossing-based scoring method aligns well with modern quantitative analysis.

Diagnostically, the D-15 demonstrates a sensitivity of 58% and specificity of 100% for moderate-to-severe CVD (n=52). The 100% specificity means a failed D-15 is a definitive finding. Repeatability is strong, with a reported kappa coefficient of κ=0.84, confirming good test-retest reliability.

One limitation to keep in mind: patients with severe CVD can sometimes learn to pass the D-15 after repeated exposure. This practice effect is clinically important in occupational screening contexts where retesting occurs. If you suspect a learned response, supplement with additional testing methods.

The Lanthony Desaturated D-15: A Two-Step Protocol

The Lanthony Desaturated D-15 is a companion test that uses lower-saturation (paler) caps. Because the color differences between caps are subtler, this version is more sensitive to mild or early color defects that the standard D-15 would miss.

Two scenarios call for its use. First, when a patient passes the standard (saturated) D-15 but you still suspect mild CVD based on symptoms or risk factors. Second, when monitoring patients for early acquired defects from drug toxicity or progressive retinal disease.

The recommended clinical protocol is straightforward: administer the saturated D-15 first. If the patient passes but remains a borderline or at-risk case, follow with the desaturated version. This two-step approach is cost-effective and avoids over-testing patients with obvious defects while catching subtle cases.

The desaturated version is particularly valuable for detecting early tritan (blue-yellow) defects associated with glaucoma, diabetic retinopathy, and optic nerve disease. These conditions often affect the S-cone pathway first, and the desaturated D-15 can identify changes before they become clinically apparent on standard testing.

Key Benefits and Clinical Advantages of the Farnsworth D-15

Speed and practicality: The test completes in under five minutes, far faster than the FM 100 Hue Test, making it viable for routine clinic flow without disrupting your schedule.

Comprehensive axis detection: The D-15 identifies protan, deutan, and tritan defects in a single test, a clear advantage over Ishihara plates, which miss tritan deficiency entirely.

Congenital and acquired CVD detection: The test applies across a wide patient population, from pediatric screenings to monitoring elderly patients on systemic medications with known ocular toxicity.

Repeatability: A kappa coefficient of κ=0.84 supports confidence in serial monitoring of progressive conditions. Changes in results reflect genuine changes in color vision.

Insurance billing: As an extended color vision test, the D-15 offers greater reimbursement than basic plate tests, supporting the financial case for thorough color vision assessment.

FDA-approved and military-validated: These credentials carry weight in both occupational and clinical settings where documentation standards matter.

Clinical decision-making: Results help practitioners counsel patients on occupational limitations, refer for further workup, or adjust medications based on objective CVD classification rather than subjective complaints.

AI-based screening tools continue to grow, but the physical D-15 remains the gold-standard classification tool for color vision deficiency. The test bridges traditional hands-on assessment with the objective, repeatable data that modern clinical practice demands.

Conclusion: A Trusted Tool for Complete Color Vision Assessment

The Farnsworth D-15 is a fast, reliable, and diagnostically comprehensive color vision test for both congenital and acquired CVD. Three core reasons justify its place in every practice: it classifies defect type and severity, it monitors disease progression over time, and it meets occupational and clinical documentation standards.

For borderline or at-risk patients, pairing the D-15 with the Lanthony Desaturated version creates a complete two-step protocol that catches subtle defects without over-testing.

Good-Lite has been a trusted leader in vision testing since 1930, and our FDA-approved Farnsworth D-15 reflects that commitment to clinical accuracy. Explore the D-15 on our product page, or contact our clinical support team for guidance on integrating color vision testing into your practice.