The correlation of pupil size measured by Colvard pupillometer and Orbscan II.

Purpose: To assess the correlation of pupil sizes measured under different illuminations by Colvard pupillometer and the Orbscan II system and to determine the factors that may influence pupil sizes.

Methods: The study comprised 162 eyes of 162 patients with a mean age of 34.6 +/- 10.6 years (range: 16 to 65 years). The photopic pupil sizes were measured with Orbscan II (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. Spherical equivalent of the manifest refraction was used to evaluate its correlation with the pupil size.

Results: The mean sizes of low mesopic and high mesopic pupil measured by Colvard pupillometer were 6.08 +/- 0.68 mm and 4.80 +/- 0.79 mm, respectively. The mean pupil size measured by Orbscan II was 3.87 +/- 0.61 mm. The pupil sizes were negatively correlated with age, but not correlated with refractive error when using multiple linear regression. Low mesopic pupil sizes were only moderately correlated with pupil sizes measured by Orbscan II (low mesopic pupil size [mm] = 0.755 x Orbscan II pupil size [mml + 3.13, r = 0.67). If > 4.5-mm pupil size measured by Orbscan II is used as the cut-off value for detecting low mesopic pupil sizes > 6.5 mm, there will be a sensitivity of 48.15% and a specificity of 93.97%.

Conclusions: Pupil sizes measured with the Orbscan II were only moderately correlated with low mesopic pupil sizes measured with Colvard pupillometer. The Orbscan II is not a preferred tool for estimating low mesopic pupil sizes.