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Tests vary in identifying glaucoma progression
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Three tests used in glaucoma diagnosis and management demonstrated varied results in a study recently published in Investigational Ophthalmology and Visual Science.
Banegas and colleagues conducted an observational cohort study to assess agreement between spectral-domain optical coherence tomography (SD-OCT), optic disc stereo photography and standard automated perimetry (SAP) in glaucomatous progression detection.
Researchers used a visual field test, optic disc stereo photography (TRC-NW7SF fundus camera, Topcon) and Cirrus SD-OCT (Carl Zeiss Meditec) to image 148 patients and 246 eyes. Tests were performed every 6 to 12 months for an average of 31.8 months.
Researchers determined glaucomatous progression by various methods; they used masked assessment for the stereo photographs, guided progression analysis (GPA) software for OCT images and a Humphrey field analyzer GPA for SAP images.
After collecting the images and progression data, researchers analyzed agreement.
"Agreement among the different methods was reported using the κ coefficient, adjusted prevalence-adjusted bias-adjusted κ (PABAK), Gwet's first-order agreement coefficient (AC1), overall percentage agreement (OPA), Cicchetti-Feinstein indices percentage of positive agreement (Ppos) and percentage of negative agreement (Pneg)," they explained.
"The three methods obtained acceptable agreements outcomes in terms of PABAK, AC1 and OPA," the authors concluded. "However, most cases with detectable changes were identified by only one examination method resulting in low Ppos. Measures of agreement showed a trend toward better agreement between photos and visual fields than by photos and SD-OCT. SD-OCT parameters reflected a tendency toward better agreement with stereo photos than with visual field. Finally, higher levels of agreement between tests were obtained when analyzing with OCT trend parameters compared to OCT event parameters.
Disclosure: Banegas reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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Derek MacDonald, OD, FAAO
Determining progression in a disease whose definition includes that criterion is critical, yet challenging. Banegas and colleagues considered the structural (clinical optic nerve head assessment and objective ONH/retinal nerve fiber layer imaging) and functional (automated visual field analysis) tests commonly employed in the diagnosis and monitoring of glaucoma and demonstrated that while inter-test correlation may be mediocre, their relative value is determined by disease severity.
In their entire cohort, more progression was noted by OCT than by ONH or automated visual field (AVF) assessment. Subanalysis indicated that most progression by OCT occurred in the ocular hypertensive and glaucoma suspect population (who, given the authors’ definition, likely had pre-perimetric disease), while progression by AVF was more common in patients with glaucoma.
This reinforces the importance of leveraging both structural and functional assessment, weighting each depending upon the clinical presentation. In pre-perimetric and early glaucoma with a relatively robust RNFL, the axial resolution of OCT is invaluable; in more advanced disease, the logarithmic AVF scale amplifies loss that structural analysis cannot detect.
Tests of structure and function remain complementary. Clinicians would be wise to employ both, early and often, recognizing that AVF analysis remains vital in the management of advanced disease. However, if you don’t know where you started…
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