Detecting Glaucoma Progression using a Combined Structure and Function Index: Comparison with the Guided Progression Analysis(GPA)

Abstract

 

Purpose

 

To compare the ability for detecting glaucoma progression of a combined index of structure and function and the Guided Progression Analysis (GPA).

 

Methods

 

The study included 154 eyes of 111 patients with glaucoma from the Diagnostic Innovations in Glaucoma Study (DIGS) followed for an average of 3.5 ± 0.8 years. An additional group of 50 eyes from 25 healthy subjects followed for an average of 1.9 ± 0.7 years was used to evaluate specificity. All patients had testing with standard automated perimetry (SAP) and spectral domain optical coherence tomography (OCT) during follow-up, with an average of 6.8 ± 2.2 visits. Glaucomatous visual field progression (likely progression) was assessed using the Humphrey Field Analyzer (HFA; Carl Zeiss Meditec) Guided Progression Analysis (SAP-GPA). Retinal nerve fiber layer progression (likely progression) was determined using Cirrus (Carl Zeiss Meditec, Inc., Dublin, CA) OCT-GPA. Data from SAP and OCT were combined to obtain an index estimating retinal ganglion cell counts (RGC index), according to a previously described method. ^(1,2) For the RGC index, progression was defined by a statistically significant slope (P<0.05).

 

Results

 

From the 154 eyes, 11 (7%) showed progression on OCT-GPA, 16 (10%) showed progression on SAP-GPA and 39 (25%) had progression detected by the RGC index (Figure 1). For the 2 eyes progressing by both SAP-GPA and OCT-GPA, the RGC index detected progression in 2 (100%) of them. In the normal group, specificity values were 100%, 98% and 94% for the SAP-GPA, OCT-GPA and RGC index, respectively.

 

Conclusions

 

A combined index of structure and function was able to detect a larger number of glaucomatous eyes as progressing compared to SAP-GPA or OCT-GPA, while retaining high specificity.  

 

Figure 1. Proportional Venn diagram illustrating the number of eyes detected as progressing according RGC index compared to those deemed to be progressing by SAP-GPA and OCT-GPA.

 

 

Figure 2. A. Boxplot illustrating the rates of change in estimated number of retinal ganglion cell (RGC) in progressing and non-progressing eyes classified according to standard automated perimetry Guided Progression Analysis (SAP-GPA). B. Boxplot illustrating the rates of change in estimated number of retinal ganglion cell (RGC) in progressing and non-progressing eyes classified according to OCT-GPA.