The Correlation of Pupil Size Measured by Colvard Pupillometer and Orbscan Ii

Purpose: To assess the correlations of pupil sizes measured under different illuminations by Colvard pupillometer and Orbscan II system and to determine the factors that may influence pupil sizes. Patients and Methods: 324 eyes of 162 subjects with a mean age of 34.6 ± 10.6 years ( range: 16 to 65 years) were enrolled. The photopic pupil sizes were measured with Orbscan II system (363 lux). The high mesopic and low mesopic pupil sizes were measured by Colvard pupillometer under 60.5 and 0 .15 lux of illumination respectively. The spherical equivalents of the manifest refraction were collected and compared. Results: The mean sizes of low mesopic and high mesopic pupil measured by the Colvard pupillometer were 6.090.69mm, 4.840.78mm, respectively. The mean pupil size measured by the Orbscan II system was 3.900.62mm. The pupil sizes were negatively correlated with age but not correlated with refractive errors. The low mesopic pupil sizes were only moderately correlated with Orbscan II-measured pupil sizes ( low mesopic pupil size (mm) = 0.735 x Orbscan II pupil size(mm) + 3.20, r2 = 0.411). If we use the Orbscan II-measured pupil size 4.5mm as a cut-off value for detecting low mesopic pupil sizes 6.5mm, there will be a false positive rate of 9.9% and a false negative rate of 40.5%. Conclusion: The pupil sizes measured with Orbscan II system were only moderately correlated with low mesopic pupil sizes. The Colvard pupillometer may provide a better measurement of low mesopic pupil size than that estimated by Orbscan II system