Journal of Clinical Medicine Article Global Glaucoma Staging System (GGSS): A New Method to Simultaneously Assess the Severity of Both Functional and Structural Damage in Glaucoma Paolo Brusini   Citation: Brusini, P. Global Glaucoma Staging System (GGSS): A New Method to Simultaneously Assess the Severity of Both Functional and Structural Damage in Glaucoma. J. Clin. Med. 2021, 10, 4414. https:// doi.org/10.3390/jcm10194414 Academic Editor: Brent Siesky Received: 2 August 2021 Accepted: 23 September 2021 Published: 26 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Ophthalmology Health Clinic “Città di Udine”, 33100 Udine, Italy; brusini@libero.it Abstract: Background: The classification of damage in glaucoma is usually based either on visual field or optical coherent tomography (OCT) assessment. No currently available method is able to simultaneously categorize functional and structural damage. Material and Methods: In this study, 283 patients with chronic open-angle glaucoma (OAG) at different stages and 67 healthy subjects were tested with both standard automated perimetry and spectral domain OCT for retinal nerve fiber layer (RNFL) assessment. The visual field data were classified using the Glaucoma Staging System 2, whereas OCT results were processed with the OCT Glaucoma Staging System. These data were used to create a new staging system (global glaucoma staging system, GGSS), in which the severity of visual field and RNFL damage is reported on the Y and X axis, respectively. The GGSS was tested in a different sample of 147 patients with manifest OAG, 56 with preperimetric glaucoma and 43 normal subjects. A six-stage clinical classification, based on the analysis of visual fields and optic disc appearance, was used as gold standard. Results: The GGSS was able to correctly classify in the same stage or within the immediately adjacent stages 145 cases on 147 (98.6%). Fifty-four preperimetric cases (96.4%) were classified as borderline or abnormal (Stage 1 or 2). Here, 41 normal eyes out of 43 were correctly classified as Stage 0, with a specificity of 95.3%. Conclusions: Preliminary results from this study are encouraging and suggest that the new GGSS is able to provide information concerning the severity of structural and functional damage in an integrated manner. Keywords: classification systems; chronic open-angle glaucoma (OAG); visual field; optical coherent tomography (OCT); structural and functional damage 1. Introduction Chronic open angle glaucoma (OAG) is a progressive disease which can slowly, but irreversibly, damage the patient’s optic nerve and visual function up to total visual impairment. Visual field and optic disc examination are thus important, both for an early diagnosis of glaucoma and for the definition of the severity of the disease. Visual field testing with standard automated perimetry (SAP) is currently the most commonly used method to quantify glaucomatous damage. On the other hand, modern spectral-domain optical coherence tomography (sd-OCT) instruments are able to accurately analyze the optic disc, the peripapillary retinal nerve fiber layer (RNFL), and the macular ganglion cells (RGCs), thus providing a better diagnostic ability for discriminating between healthy eyes and glaucomatous eyes. Several staging methods for categorizing glaucomatous functional damage severity, and staging the RNFL damage assessed with the glaucoma diagnosis (GDx) or OCT, are currently available [1–9]. The most popular systems to stage the functional damage include: (1) the three-stage Hodapp–Parrish–Anderson method, which is based on the assessment of the mean deviation (MD) value, number of depressed points in the pattern deviation map, and proximity of defects to fixation point [3]; (2) the five-stage Mills et al. staging system, which is an evolution of the former [4]; (3) the AGIS method, which takes the number of depressed points in various areas in the central visual field into account, and provides a J. Clin. Med. 2021, 10, 4414. https://doi.org/10.3390/jcm10194414 https://www.mdpi.com/journal/jcm