Clinical applicability of the international classification of disease and related health problems (ICD-9) glaucoma staging codes to predict disease severity in patients with open-angle glaucoma

Purpose: The aim of the study was to determine how the International Classification of Disease and Related Health Problems (ICD-9) Glaucoma Staging Codes (GSC) relate to visual field global indices and average retinal nerve fiber layer (RNFL) thickness in patients with primary open-angle glaucoma (POAG). Methods: Over a 6-week period, charts of consecutive patients were prospectively reviewed. Included patients had optic nerve head damage consistent with glaucoma as well as reliable functional and imaging tests. Patients were divided into early-stage, moderate-stage, and severe-stage glaucoma using the ICD-9 GSC guidelines. Relationships between mean deviation (MD), pattern SD (PSD), average RNFL thickness, and the staging system were evaluated. Results: A total of 616 patient charts were evaluated and 135 patients met the inclusion criteria. Of the 135 patients, both eyes (270 eyes) were evaluated and the worse eye (by MD) was included in the analysis. Using the ICD-9 GSC guidelines as a basis for defining severity, MD was significantly lower in the severe-stage compared with the moderate-stage group (P<0.01) and in the moderate-stage when compared with the early-stage group (P=0.020). PSD was significantly higher in the severe-stage compared with the moderate-stage group (P<0.01) and in the moderate-stage compared with the early-stage group (P<0.01). Average RNFL thickness was not significantly lower in the severe-stage compared with the moderate-stage group (P=0.05); however, it was significantly lower in the severe-stage and moderate-stage groups compared with the early-stage group (P<0.01). Conclusions: ICD-9 GSC showed a significant relationship between worsening visual field indices and RNFL loss with increasing disease severity in patients with POAG.