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The ‘C Test’ for tritan threshold detection: design and normal values

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Session Details

Session Title: Presented Poster Session: Quality of Vision/Miscellaneous

Venue: Poster Village: Pod 3

First Author: : R.Littlewood AUSTRALIA

Co Author(s): :                  

Abstract Details


Tritan tests are not well suited to routine clinical practice, being merely semi-quantitative (Richmond HRR, D15), time consuming (100 Hue), or expensive (Cambridge colour test). The C test is a novel pseudoisochromatic test with 10 perceptually ordered tritan plates. Each foreground is a geometrically similar tritan ring (430 nm), resembling a Landolt C. The task is to identify in which of 8 possible positions the break lies for each plate. It requires 800 Lux of artificial daylight and a LOCS III grading. The test was evaluated to determine its practicality and reliability in clinical practice, and its normal values.


The Midland Eye Clinic, Perth, Australia.


The C test, LOCS III grading, and Logmar acuity were recorded monocularly in all subjects newly referred to an ophthalmology clinic during 3 months (n=568 eyes). Data from eyes free of relevant pathology (n=355) was used to determine normal limits. The correlation between LOCS III grading and both Logmar acuity and the C score was analysed with Spearman rank correlation. The effect of age on C score was evaluated in the 136 pseudophakic eyes within the normal population. They were stratified into three age ranges (50-63,64-76,77-89) and the C score distributions compared using the Kruskal-Wallis H test.


Bilateral C tests took < 90 seconds in most cases. The correlation with nuclear colour (NC) was similar for C test (-0.58) and Logmar acuity (0.57). The strongest correlation was between posterior subcapsular cataract and Logmar acuity (0.68). The correlation between nuclear opalescence and cortical cataract was stronger for Logmar acuity (0.54, 0.53) than for C score (-0.48, -0.40). The lower limit of the C score was 9 when NC < 3, 7 when NC = 3, but undetermined for higher grades of NC due to increasing sore variability. Score distributions in the three pseudophakic age ranges were similar (p=0.486).


The higher correlation of C score with NC than other LOCS domains is consistent with a threshold response limited by chromatic rather than achromatic contrast. The high correlation between posterior subcapsular cataract with Logmar acuity but not C score is consistent with the absence of blue cones from the central fovea. The highest and most consistent C scores were obtained when the subjects were instructed to move their gaze around the ring to discover the break. The C test provided consistent ordinal measures of koniocellular function in a time pressured environment. It is available from Vanguard Press, Perth, Australia

Financial Disclosure:

receives non-monetary benefits from a company producing, developing or supplying the product or procedure presented.

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