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Standard structural measures can identify progression in advanced glaucoma
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Structural changes within advanced glaucoma can be identified by monitoring macular retinal ganglion cell-inner plexiform layer, and 3D whole-volume Bayesian-kernel detection scheme change shows promise in detecting progression in advanced disease, according to researchers in Investigative Ophthalmology & Visual Science.
Researchers included 35 eyes of 35 patients with advanced glaucoma and 46 eyes of 30 healthy subjects.
Circumpapillary retinal fiber layer thickness (cpRNFL), minimum rim width (MRW) and macular retinal ganglion cell-inner plexiform layer (GCIPL) thicknesses were measured using the San Diego Automated Layer Segmentation Algorithm (SALSA).
In advanced-glaucoma eyes, the mean rates of cpRNFL, MRW and macular GCIPL change were -0.08 µm/y, -0.29 µm/y and -0.18 µm/y, respectively, according to researchers.
No significant difference was found between the mean rate of loss of cpRNFL and MRW in advanced-glaucoma eyes and healthy eyes. The mean rate of macular GCIPL loss was typically larger in advanced-glaucoma eyes than in healthy eyes, but the difference in mean rates between groups was not significant.
“Our results suggest than even in very advanced glaucoma, structural loss can be detected in some eyes using standard global structural measures,” the researchers wrote.
Macular GCIPL had the highest proportion of eyes with detectable change followed by MRW and cpRNFL.
The researchers concluded that monitoring macular GCIPL and 3D whole-volume BKDS change shows promise for identifying progression in advanced glaucoma. – by Abigail Sutton
Disclosure: Belghith reported no financial disclosures. Please see the full study for all remaining authors’ relevant financial disclosures.
Perspective
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Derek MacDonald, OD, FAAO
In the early 2000s, Weinreb introduced the concept of the glaucoma continuum, staging disease severity from undetectable retinal ganglion cell dysfunction through advanced functional impairment. As a clinician, I find the extremes of this continuum (early glaucoma diagnosis and detecting progression in advanced stage disease) challenging, but vitally important.
Objective imaging has facilitated our ability to detect pre-perimetric glaucoma and has led to the conventional wisdom of leveraging OCT earlier and automated perimetry later, when retinal nerve fiber layer (RNFL) thickness approaches its 50-micron floor. However, visual fields vary significantly in advanced disease, and this imparts uncertainty at a time when certainty is critical.
Enter the macula. Although Hood and others have proven that central damage is quite common in early glaucoma, the sheer number of retinal ganglion cells within the macula make the papillomacular bundle relatively resistant to damage, which makes ganglion cell/inner plexiform layer (GCIPL) analysis very valuable in advanced disease.
While RNFL and 24-degree visual field analyses remain the cornerstones of structural and functional assessment in early to moderate glaucoma, this study and others suggest that monitoring GCIPL and 10-degree visual field status – providing that timely and accurate baselines have been established – allows the quantification of progression to continue through the entire glaucoma continuum.
References:
Hood DC, et al. Prog Retin Eye Res. 2007;26:688–710.
Hood DC, et al. Prog Retin Eye Res. 2013;32:1–21. doi: 10.1016/j.preteyeres.2012.08.003.
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