Influence of pupil dilation on repeatability of scanning laser polarimetry with variable and enhanced corneal compensation in different stages of glaucoma.

Purpose: To evaluate the influence of pupil dilation on repeatability of scanning laser polarimetry with variable (GDx-VCC) and enhanced (GDx-ECC) corneal compensation, in different stages of glaucoma.

Methods: One eye of each of 37 Caucasian participants [14 healthy and ocular hypertensive subjects with mean deviation (MD) <2 dB, 11 glaucoma patients with MD 6 to 12 dB, and 12 glaucoma patients with MD >15 dB] was imaged 5 times with both GDx-VCC and GDx-ECC, before and after pupil dilation.

Results: No statistically significant alteration was found for any parameter or most coefficients of variation in any group, or in the total study population, due to pupil dilation. Intraclass correlation was similar with both compensation techniques: it varied between 98.5% and 99.2% before, and 97.3% and 99.1% after pupil dilation for all participants. Intrasession variability was below 6 mum for all parameters and all groups irrespective of corneal compensation and pupil dilation. By using GDx-ECC, a statistically significant trend for higher coefficient of variation values in more severe stages of glaucoma was found, irrespective of pupil dilation (Jonckheere-Terpstra test, P<0.026, for all parameters). With GDx-VCC this trend was not seen for 2 of the 3 parameters before pupil dilation, but did appear for all parameters in mydriasis (P<0.002).

Conclusions: Repeatability of GDx-VCC and GDx-ECC is similar, and is satisfactory for clinical purposes; it is only minimally influenced by pharmacological mydriasis. However, repeatability of the measurement decreases with increasing severity of glaucoma. This characteristic is better detectable with GDx-ECC than with GDx-VCC.