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F. C. Moura, F. A. Medeiros, Má. L. R. Monteiro; Evaluation of Retinal Nerve Fiber Layer Measurements Using Scanning Laser Polarimeter With Variable Corneal Compensation (GDx VCC) and Enhanced Corneal Compensation (GDx ECC) in the Eyes With Band Atrophy of the Optic Nerve. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2466.
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© ARVO (1962-2015); The Authors (2016-present)
To compare enhanced corneal compensation (ECC) and variable corneal compensation (VCC) in scanning laser polarimetry (SLP-GDx) measurements of retinal nerve fiber layer (RNFL) in the eyes with band atrophy (BA) of the optic nerve and normal control eyes.
The study included 128 eyes (55 eyes with BA of the optic nerve and 73 eyes age- and sex-matched healthy subjects). RNFL thickness scans were obtained using the commercially available GDx VCC and GDx ECC. The severity of visual field defect in patients with BA was evaluated by the temporal mean defect (TMD), calculated as the average of the 22 values of the temporal total deviation plot of the SAP 24-2 test, excluding the 2 points immediately above and below the blind spot. RNFL values with GDx VCC were compared to those from GDx ECC using paired t test and values of eyes with BA measured both with GDx VCC and GDx ECC were also compared with those of normal controls using unpaired Student’s t tests. Receiver operating characteristic (ROC) curves and sensitivities at fixed specificities were calculated for each parameter. Pearson correlation coefficients were used to evaluate the relationship between RNFL thickness parameters and severity of visual field loss as measured by the TMD. A P value less than .05 was considered statistically significant.
In GDx VCC and GDx ECC, all RNFL thickness parameters were significantly lower in eyes with BA compared with normal eyes (p<0.001). In BA patients, inferior average was higher with ECC than VCC (p=0.03) and temporal average was lower with ECC than VCC (p<0.001). TSNIT average has largest AUC in both corneal compensation methods. The AUC of the nasal average parameter was significantly larger for measurements with GDx VCC than with GDx ECC (p=0.03). No statistically significant difference was found for temporal average parameter. Lower values of TMD, indicating more severe visual field loss, were associated with lower RNFL thickness measurements. In VCC, the highest correlation was observed for the parameter superior average (r = 0.73; R² = 53.2%; p<0.001). In ECC, the highest correlation was observed for the parameter TSNIT average (r = 0.71; R² = 50.4%; p<0.001).
GDx VCC and GDx ECC RNFL thickness measurements were able to differentiate eyes with BA from normal controls. However, GDx ECC poorly discriminate RNFL loss in the nasal sector when compared to GDx VCC.
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