Structure and function combined is best for detecting, discriminating glaucoma

Sep 21 2012

By Sarah Guy, medwireNews Reporter

An index that combines structure and function measurements can detect perimetric and preperimetric glaucoma more accurately, and can differentiate early, moderate, and advanced disease more successfully than systems that consider either variable alone, report researchers.

The combined index of structure and function (CSFI) considers more than standard automated perimetry (SAP) measurements, which have been relied on until now but may underestimate the severity of damage in early disease.

"The CSFI has several desirable properties for use as a staging index," explain Felipe Medeiros (University of California, San Diego, USA) and co-workers. "It discriminates well among the different stages of disease and has an intuitive interpretation as the overall percent loss of neuronal tissue.

The team compared data for 333 glaucomatous eyes - 295 with perimetric glaucoma and 38 with preperimetric glaucoma - with data for 165 eyes from healthy individuals. All eyes underwent ophthalmologic testing, including SAP.

While visual field defects on SAP are known to associate with retinal ganglion cell (RGC) loss, studies have shown that as many as 40‑50% of RGCs may need to be lost before this test can detect changes, explain the researchers.

Mean estimated RGCs were 524,545 in the perimetric group, 748,731 in the preperimetric group, and 973,120 in the healthy eyes, and RGCs decreased significantly with age, at a rate of 9249 per year in healthy individuals, remark the researchers in the Archives of Ophthalmology.

Receiver operating characteristic analysis calculated an area under the curve (AUC) score of 0.94 (where 1 is perfect discrimination) for distinguishing glaucomatous from healthy eyes using the CSFI. This was significantly higher than the AUC scores of the other indices tested, including the visual field index.

The CSFI also identified perimetric glaucoma significantly more accurately than did the mean deviation of retinal nerve fiber layer, with an AUC score of 0.96 versus 0.93, and identified preperimetric glaucoma significantly more accurately than did the visual field index, with an AUC score of 0.85 versus 0.51.

The CSFI was superior at distinguishing the 189 eyes with early visual field loss from the 49 with moderate damage and 57 with advanced damage, with AUC scores ranging from 0.94 to 0.96 compared with 0.70 to 0.77 for the other diagnostic indices.

"Future studies should be performed to attempt to correlate proposed staging systems to results of these tests or to develop staging systems based on results of tests directly measuring functional impairment in glaucoma," the authors conclude.

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