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N. T. Choplin, Q. Zhou, V. Atkinson; Enhanced Corneal Compensation (ECC) Greatly Reduces Atypical Scanning Laser Polarimetry Results Compared to Variable Corneal Compensation (VCC). Invest. Ophthalmol. Vis. Sci. 2008;49(13):4642.
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Variable corneal compensation (VCC) is a method for removing the anterior segment birefringence component from the scanning laser polarimetry (SLP) signal in order to isolate the retinal nerve fiber layer component, improving the accuracy of the technique for diagnosing glaucoma. A number of "atypical" scans have been identified with VCC, making scan interpretation difficult. Enhanced corneal compensation (ECC) is a software method designed to reduce atypia. This study was designed to identify the risk factors for atypical scans and to determine the ability of ECC to reduce their occurrence.
Patients undergoing SLP at Eye Care of San Diego were imaged with both VCC and ECC on the same day. Inclusion criteria included image quality score of 7 or greater. One eye was selected at random if both eyes qualified. A "Typical Scan Score" (TSS), ranging from 0 (highly atypical) to 100 (highly typical) was generated from the scan data; atypia was defined as either 1) TSS 60 or less or 2) TSS 40 or less. Descriptive statistics were generated, including age and ancestry. The rate of atypia was determined for VCC and ECC. Multivariate analysis was conducted to determine risk factors for atypia. p < 0.05 was the level of statistically significance.
370 eyes from 370 patients imaged during the 8 month period from 3/16/07 to 11/12/07 were included. 70% of patients were white, 9.5% were black, and the remiander mostly Hispanic. The average TSS for VCC was 80.13, improving to 96.66 with ECC (p = 0.000). Atypia (TSS 60 or less) was observed in 18.7% of eyes with VCC and 2.2% of eyes with ECC (p < 0.000). 5.7% (2/35) of eyes from black patients had TSS 60 or less with VCC; in non-blacks the rate was 20.0 % (67/335) (p=0.039, chi-square). The rates for ECC were 0% (0/35) for blacks and 2.4% (8/335) for non-blacks. There were no eyes from black patients with TSS 40 or less; for non-blacks the rate of TSS 40 or less was 10.7% (36/335) for VCC and was 1.2% (4/335) for ECC. The differences between blacks and non-blacks were statistically significant for VCC only (p = 0.041, chi-square). Increasing age was associated with atypia for VCC only (p=0.006).
Atypical scans are associated with increasing age and non-black race when VCC is employed. ECC is very effective at reducing atypia. Further work is needed to determine the effect of ECC on the accuracy of SLP for diagnosing glaucoma.
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