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15-11-2018 | Ophthalmology | News | Article

Current glaucoma staging systems underestimate disease severity

medwireNews: Current glaucoma staging systems based on 24-2 (or 30-2) visual fields underestimate disease severity and the presence of macular damage when compared with 10-2 visual fields and high-resolution macular imaging, US researchers report.

Carlos Gustavo De Moraes (Columbia University Medical Center, New York) and co-investigators say the implications of their findings “may extend beyond estimating the level of macular damage […] to the quality of care delivered”, because current International Statistical Classification of Diseases and Related Health Problems, Tenth Revision codes are based on 24-2 (or 30-2) visual fields.

“This limited approach may affect not only billing and reimbursement, but most importantly how frequently these patients are seen and tested in clinical practice”, the authors write in JAMA Ophthalmology.

The cross-sectional study included 57 eyes of 57 participants with glaucoma and 24-2 mean deviation (MD) better than –6 dB. Of these, 84% had macular damage according to a combination of topographically matching spectral-domain optical coherence tomography (SD-OCT) and 10-2 standard automated perimetry (SAP), which the researchers explain uses a denser grid than 24-2 SAP (2x2º vs 6x6º) to assess damage within the central 10º of the visual field.

Among the 48 eyes with macular damage, the average 24-2 MD was −2.5 dB compared with −3.0 dB for the 10-2 MD, and the mean visual field index (VFI) was 94.2%.

Among the current staging systems evaluated, De Moraes and team found that the Hodapp-Parrish-Anderson system classified 71% of the 48 eyes with macular damage as having no, minimal or early-stage defects.

The VFI component of the Glaucoma Visual Field Staging System classified 81% of eyes with macular damage as having early defects, while 69% of eyes with macular damage were classified as stage 0, borderline or stage 1 using the Brusini system.

When considering the importance of the macula for day-to-day activity and quality of life, the investigators say that their findings “suggest a fundamental flaw inherent to systems that aim to define glaucoma severity based exclusively on 24-2 or 30-2 visual fields”, such as those tested in the current analysis.

They continue: “Most eyes commonly classified as having early disease may in fact require reclassification to severe glaucoma if the macula were evaluated with more adequate tools and without overrelying on summary metrics (such as MD, [pattern standard deviation], and VFI).”

De Moraes et al conclude that if their results can be confirmed and are applicable to other patients, “new systems using macular measures (from 10-2 and spectral-domain optical coherence tomography results) might improve staging of glaucoma severity.”

They add: “The implementation of such new systems should be considered by clinicians, researchers, and public health authorities.”

By Laura Cowen

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