Barkana et al. present an interesting study on two perimetry devices, in which they evaluate the usefulness of subsets of specific test points instead of all test points for glaucoma clinical trials. The background for their research is the need for improved visual field endpoints for neuroprotection clinical trials.
They included 30 patients (mean age 70.2 years) with glaucomatous neuropathy based on imaging who performed a pair of 24-2 tests with each the Humphrey (HVF) and the Compass perimeters. The latter device is a recently commercialized perimeter which performs VF testing while continuously tracking the fundus using a scanning laser ophthalmoscope and placing each stimulus according to its exact fundus coordinates, with the aim of reducing test variability.
Non-weighted mean deviation (MD) was calculated for the whole field and separate vertical hemifields, and again after censoring of points with low sensitivity (MDc) and subsequently including only 'abnormal' points. They found that restricting analysis to particular subsets of points of interest after censoring points with low sensitivity, as compared with using the familiar total field MD, provided outcome measures with a broader range of MD, a reduced SD. The obtained data set was, therefore, more homogenous, without worsening test-retest variability.
Despite the robust methodology, several limitations exist. The sample size is small. The Compass perimeter, despite a growing body of evidence, is new and largely untested. MDs were similar between HFA and Compass before censoring, for the whole field and for each hemifield. It remains to be understood why test-retest variability was better with the Compass for raw and sensitivity-censored parameters (implying better inter-test agreement), but better with HVF when only abnormal points were included.
In conclusion, this study offers a novel framework for the construcion of several potential VF endpoints for use in glaucoma trials.