Make sure your GDx tests are performed under similar conditions in regard to any medications that affect your pupil size.

Influence of Pupillary Diameter, Ciliary Muscle Tone, and Ambient Light on Nerve Fiber Layer Measurements With Scanning Laser Polarimetry

Paranhos A Jr, Silvestre AM, Passerotti CC, Martins EM, Mello PA, Prata JA Jr, Shields MB.

PURPOSE:: To evaluate the influence of the pupillary diameter, ciliary muscle tone, and room light on nerve fiber layer measurements with the scanning laser polarimeter (GDx).

METHODS:: One randomly selected eye of ten normal volunteers was examined with the GDx in a two-day protocol under eight testing conditions (pilocarpine 1%, phenylephrine 10%, tropicamide 1%, or no drops with room lights on or off). The twelve parameters, obtained by the GDx, were compared under the eight testing conditions, using two way ANOVA for repeated measurements and Tukey HSD post hoc test.

RESULTS:: Ten of the twelve parameters were statistically significantly different (P < 0.05) when measured under the three medication or no medication conditions, controlling for the ambient light status. There were no significant differences when measured with the light on or off, controlling for use of drops.

CONCLUSIONS:: Nerve fiber layer measurements with the GDx were influenced by drugs affecting pupillary diameter, but not by the status of room light or ciliary muscle tone.

J Glaucoma. 2005 Apr;14(2):124-127.