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Editors Selection IGR 23-2

Combined Structure and Function Measurement: Stratus OCT+HRT+VF and progression

Comment by David Greenfield on:

46630 Evaluation of retinal nerve fiber layer progression in glaucoma: A prospective analysis with neuroretinal rim and visual field progression, Leung CKS; Liu S; Weinreb RN et al., Ophthalmology, 2011; 118: 1551-1557

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Detecting progressive loss of the retinal ganglion cells and their axonal fibers is a critical aspect of glaucoma diagnosis, monitoring, and management, and is facilitated by digital ocular imaging technologies. Many studies have demonstrated that optical coherence tomography (OCT) is capable of detecting progressive glaucomatous retinal nerve fiber layer (RNFL) atrophy. Thus, the quantitative measures provided by OCT may serve as a useful adjunct to longitudinal assessment of visual function with standard automated perimetry and optic nerve appearance using clinical examination and stereoscopic optic disc photography in detecting glaucoma progression. In the present study, Leung et al. (1385) examine the performance of progression detection and the rate of change of RNFL (Stratus OCT), neuroretinal rim (Heidelberg Retina Tomography, HRT), and visual field measurements among 108 glaucomatous eyes. Patients were followed up every four months for at least 2.9 years. Linear regression analyses were performed between visual field index (VFI), RNFL, and neuroretinal rim measurements and age, with progression defined when a significant negative trend was detected. The agreement of progression detection among the three investigations was poor. Nine percent of eyes showed progression by average RNFL thickness, 15% by global neuroretinal rim area, and 32% by VFI. Only one eye (0.9%) had progression detected by all three methods. There were large variability both within and between subjects in the rate of change of VFI (range -0.63% and -4.97% per year), average RNFL thickness (range -2.32% and -10.12% per year), and global neuroretinal rim area (range -0.61% and -8.48% per year). The authors concluded that given this variability, interpretation of RNFL, neuroretinal rim, and VFI progression always should be evaluated on an individual basis.

Assessment of the rate of progression is highly variable among persons with glaucoma and is a critical determinant for estimating the target intraocular pressure goals

Although Leung and colleagues studied time-domain OCT, advances in spectral domain OCT (SDOCT) technology have the potential to greatly enhance detection of progressive glaucomatous structural changes over time. Segmentation of retinal layers such as the ganglion cell complex consisting of the combined nerve fiber, ganglion cell, and inner plexiform layers may enhance detection of localized glaucomatous changes. The faster speed of SDOCT (65x Stratus OCT) allows high-density scanning over a large region of the macula with less motion artifact, higher resolution, and improved repeatability could improve the ability to track glaucomatous thinning over time. Preliminary data has shown that SDOCT outperforms Stratus OCT in detecting more eyes with RNFL progression and fewer eyes with RNFL improvement suggesting that SDOCT may detect changes in RNFL thickness sooner than the Stratus OCT owing to reduced measurement variability. Future studies are warranted to compare the sensitivity and specificity of RNFL thickness, optic disc topography, and visual function for detection of glaucoma progression. As emphasized in this well designed and executed study, assessment of the rate of progression is highly variable among persons with glaucoma and is a critical determinant for estimating the target intraocular pressure goals for our patients. Performing a comprehensive assessment of structure and function is critical for monitoring glaucoma progression over time.

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