Abstract
Purpose :
Recent research demonstrated that the location of parapapillary autofluorescence (PAF) partially correlates with borderline and pathologic RNFL thickness in POAG. This prospective study characterizes the evolution of RNFL bundles of normal thickness coursing over PAF areas, to determine if PAF is a marker of active RNFL thinning.
Methods :
Patients with POAG were randomly selected. Those with a condition interfering with the measurement of PAF were excluded, as were patients with non-glaucomatous optic neuropathies. PAF images and RNFL thickness profiles were acquired using a confocal scanning laser ophthalmoscope. RNFL profiles were extracted and registered on the PAF images using vascular markers. PAF areas were identified using automatic region growing with manually selected seed points. Only PAF areas identified over RNFL bundles of normal thickness were kept and labelled as "PAF areas of interest". RNFL profiles were finally reacquired 12±6 months later; these profiles were compared to the original ones to determine if significant RNFL thinning (≥10μm) occurred over the PAF areas of interest during this period.
Results :
32 fundi were initially imaged. 35 PAF areas of interest were identified on 18 of the 32 fundi. These areas were mainly located in the supero-temporal (38.1%) and the infero-temporal (38.1%) quadrants (Χ2 goodness-of-fit test compared to a uniform distribution, p=0.04), spreading over 11.8±6.46°. 6 fundi were either lost at follow-up (33.3%) or poorly re-imaged (66.7%). Mean time to reacquire the RNFL profiles of the remaining 12 fundi, containing 21 of the initial 35 PAF areas, was 12±4.28 months. Corrected for mean global RNFL thinning, RNFL bundles coursing over these areas thinned on average 11.1μm (CI 95% [1.4μm;20.9μm]; Student’s t-test, p=0.03) over 12±4.28 months. Significant RNFL thinning (≥10μm) occurred over 42.9% of the 21 PAF areas. Maximal focal RNFL thinning over these PAF areas attained on average 18.4μm (CI 95% [7.0μm;29.7μm]; Student’s t-test, p<0.01). RNFL profiles locally dipped from normal to borderline thickness (p<0.05) over 4 of the 21 PAF areas.
Conclusions :
Though the pathophysiology of PAF in POAG is still unclear, this study shows that PAF can pinpoint ongoing significant focal RNFL thinning. We thus encourage clinicians to pay closer attention to RNFL bundles coursing over PAF areas when evaluating glaucoma progression.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.