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  • Investigators assessed the normative values and test-retest variability for version 4 of rarebit perimetry. They used the software to study the central and foveal fields of 54 normal subjects, all of whom repeated the test within one month. They found it to be repeatable and reliable, especially in younger patients.

    The central field normative mean hit rate (MHR) was 86.3 percent overall, 90.6 percent for young subjects (age 21 to 45) and 81.9 percent for mature subjects (age 46 to 73). The foveal field normative MHR was 91.6 percent overall, 98.2 percent in young subjects and 85 percent in mature subjects.

    There was a significant relationship between age and MHR. For the central field test, MHR decreased 0.47 percent per year; for the fovea test, it decreased 0.67 percent per year. The age effect is likely due to the general decline in photoreceptor sensitivity with age, as well as other physiological changes, such as lens and pupil changes. External factors, such as familiarity with the modern PC mouse and fatigue, may also play a role.

    Test-retest variability was insignificant in the foveal field but significant in the central field. There was a 3.5-unit increase in central MHRs on the retest regardless of age. This could be attributed to a learning effect. Although this was statistically significant, it may not be clinically significant as it has been previously shown that the MHR was 64 percent in early primary open-angle glaucoma patients and 89 percent in controls.

    There was no significant variability among patients in the young age group. When comparing the individual test zones, there was no significant test–retest variability in the 24 zones with the exception of zone 23, which is a peripheral test area inferiorly. The effect of eccentricity of test areas on test–retest warrants further study. \

    The authors recommend an age-specific MHR normogram using normative values based on just two age groups. They conclude that this newest version of rarebit perimetry holds promise for the detection of early visual field loss due to glaucoma and macular diseases. However, more work is still required to validate the test for these conditions.