An estimated 57.5 million people worldwide are affected by primary open-angle glaucoma (POAG), and essentially all are at risk for disease progression at some point, increasing the stakes for the clinicians providing care. In the structure-vs.-function debate, no ironclad guidelines exist to determine which is best suited to detect glaucoma progression, but a new study adds more evidence that anatomical evidence is more sensitive.
A total of 194 eyes from 194 patients with a minimum of nine follow-up visits, selected from the Diagnostic Innovation in Glaucoma Study and the African Descent and Glaucoma Evaluation Study, were included. Each eye was classified according to baseline clinical signs: ocular hypertension (OHT), glaucomatous optic neuropathy only (GON), glaucomatous VF loss only and definite glaucoma (concurrent optic disc and VF defect). Progression was assessed by performing simple linear regression on global and sectorial mean deviations values generated for RNFL thickness and VF data. The proportion of eyes identified as progressing (positive rate) by RNFL thickness change and by field loss were compared within each classification.
While both parameters performed similarly among GON and definite glaucoma eyes, the positive rate obtained with global RNFL thickness was significantly greater compared to global visual field change by 33.3% and 30.8% among OHT eyes and glaucomatous field loss only eyes, respectively. This finding was consistent in the inferotemporal sector; however, similar positive rates were obtained for both parameters in the superotemporal sector.
The study concluded that although both parameters showed comparable abilities to identify progression across the different classifications, RNFL thickness assessment may be better suited to monitor progression, particularly among patients with elevated intraocular pressure and those who present with only glaucomatous VF defect at baseline.
While some eyes were identified as progressing by VF assessment, the authors suggest the results of this study demonstrate that OCT assessment of RNFL thickness may be better suited for monitoring glaucoma progression, particularly among OHT patients and those who initially present with only glaucomatous visual field defects.
“Contrary to our expectation that VF evaluation would be more likely to identify progression” in glaucomatous VF loss cases, the authors wrote, change in RNFL thickness identified 14 more of those eyes as progressing and 16 more eyes of OHT patients. “These observations may be explained by the notion that OCT is better suited to detect progression in the early stages of glaucoma, whereas [perimetry] may become more useful in the later stages of the disease. This notion, strongly pivoted on the presence of ‘floor effect’ in RNFL measurement, has been strengthened by recent studies,” in which OCT outperformed perimetry in detecting progression among early glaucoma eyes.
Although both assessments are capable of detecting progression in patients with different baseline clinical signs, the authors note that preference may be given to RNFLT assessment when prevailing circumstances permits for only a single test be done.
Abu SL, Marín-French I, Racette L. Detecting progression in patients with different clinical presentations of primary open-angle glaucoma. Journal of Glaucoma. Epub ahead of print.