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Study: SAP, SD-OCT results must be considered with clinical picture
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Researchers found both advantages and disadvantages in using standard automated perimetry and spectral domain optical coherence tomography in diagnosing glaucomatous optic neuropathy, according to a study recently published in the Journal of Glaucoma.
Rao and colleagues conducted an observational, cross-sectional study, evaluating 280 eyes of 175 patients that had been referred to a tertiary eye care facility for a glaucoma evaluation.
They utilized spectral domain optical coherence tomography (SD-OCT) RTVue (Optovue Inc.) for imaging of retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC). Researchers also used standard automated perimetry (SAP) Humphrey Field analyzer, model 750 (Zeiss Humphrey Systems).
As detailed in the study, two glaucoma experts who were masked to SAP and clinical results used digital optic disc photographs to determine the glaucomatous optic neuropathy (GON) and nonglaucomatous groups. Researchers compared SD-OCT and SAP results using sensitivity, specificity and likelihood ratios.
"We found that most of the SD-OCT parameters had better sensitivities and negative likelihood ratios to diagnose GON compared with SAP," the authors concluded. "The specificities and positive likelihood ratios of SD-OCT parameters to diagnose GON were, however, inferior to that of SAP.
"Any result on SAP or SD-OCT, therefore, needs to be interpreted along with the total clinical picture before accepting it or discarding it as a false result," they noted.
Disclosure: The authors declare no conflict of interestPerspective
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Derek MacDonald, OD, FAAO
Glaucoma is a structural disease with functional sequelae. Given its relatively long track record, standard automated perimetry (SAP, an assessment of function) has become a diagnostic and reference standard.
However, spectral domain optical coherence tomography (SD-OCT, an assessment of structure) may allow earlier diagnosis through the identification of structural defects before the onset of functional deficits. One could argue that using SAP as a diagnostic benchmark for SD-OCT puts the cart before the horse.
Rao and colleagues evaluated SAP and SD-OCT against a familiar structural reference standard: the clinical disc examination. Not surprisingly, in their cohort with early to moderate disease, SD-OCT proved more sensitive (identifying eyes with pre-perimetric glaucoma), while SAP proved more specific (identifying eyes, particularly those with anomalous optic nerve heads, as nonglaucomatous).
Perhaps most important, however, was the authors’ conclusion that no single test result can be considered in isolation. Rather, each and every piece of information must be integrated within the decision-making algorithm of the most important diagnostic instrument at every clinician’s disposal: the one between our ears.
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