Colour vision testing as an aid to diagnosis and management of age related maculopathy

Abstract

Aim: To provide a simple test that detects the onset of age related maculopathy (ARM), and can be used to monitor its severity.

Methods: Colour contrast sensitivity was measured using computer graphics techniques. Colour thresholds were measured along tritan and protan colour confusion axes in the presence of dynamic luminance noise. Thresholds were determined separately for two sizes of optotypes (6.5 degrees and 1.5 degrees). Natural pupils were used. Normal values for the test have been established.

Results: In all patients with unilateral age related macular degeneration, the smaller optotype was invisible in that eye and in almost all, the larger optotype could not be seen. In the symptomless fellow eyes (with ARM) the larger optotype thresholds were raised. The degree of loss was larger for tritan. For the smaller optotype, protan thresholds were elevated in the majority of patients. Tritan losses were greater and disproportionate to the loss seen with the larger optotype. Every person including those with minimal fundal changes had tritan test results for 1.5 degree optotypes >2 SD above the normal mean. Tritan thresholds varied with the severity of the ARM.

Conclusions: The test is sensitive, simple and quick to administer, and easy for patients. Therefore, it should be useful in detecting and monitoring elderly people with age related changes in their fundi before irreversible loss of vision has occurred.

Figure 1

(A) Changes to measured chromaticity with change of modulation depth. (B) Reduction in lens transmission as a function of age compared to the transmission of filters for ages 50, 60, 70, and 80. The filters were as follows; plastic filters provided by Lee Filters, Ltd, UK. For 50 year old data No 159, for 60 year old No 763, for 70 year old No 764, for 80 year old two layers of No 763. (C) Changes in thresholds with yellow filters in 20 year old subjects. The vertical bars are plus or minus 1 SD, and are within the symbols except for the smaller tritan optotypes.

Figure 2

(A) Normal results for smaller optotypes in an older population. The trend line equations are shown. The blue broken line is 2 SDs above the normal mean values for tritan thresholds, and the red broken line is the upper limit of normal for the protan threshold. (B) Normal results for larger optotypes in an older population. The trend line equation are shown and refer to values obtained in patients with measureable thresholds (<100%).The blue broken line is 2 SDs above the normal mean values for tritan thresholds, and the red broken line is the upper limit of normal for the protan threshold.

Figure 3

(A) Thresholds for 1.5 degree letters in patients with ARM. The upper limits of normal are transferred from figure 2. Note the difference in vertical scaling. (B) Thresholds for 6.5 degree letters in patients with ARM. The upper limit of normal is transferred from figure 2. Note the difference in vertical scale between this figure and figure 2.

Figure 4

Relation of thresholds to visual acuity. 5′ arc indicates an acuity of 1.0, and 50′, and acuity of 0.1 (this method of plotting is designed to present the result more clearly).

Figure 5

See text.