Influence of pupil size and cataract on retinal nerve fiber layer thickness measurements by stratus OCT

Aim: To investigate whether retinal nerve fiber layer (RNFL) thickness, as measured by optical coherence tomography (OCT), is influenced by pupil size and cataract. Methods: RNFL thickness was measured by means of Stratus OCT (RNFL Thickness 3.4 acquisition protocol) in a group of consecutive patients undergoing phacoemulsification and intraocular lens implantation. Measurements were taken preoperatively without pupil dilation (PR1), preoperatively with pupil dilation (PR2), and 1 month postoperatively without pupil dilation. Results: Twenty-five eyes of 25 patients were enrolled in the study and underwent statistical analysis. Pupil dilation caused RNFL thickness measurements to increase slightly in PR2 compared with PR1; the difference showed to be statistically significant in the 360-degree average measurement (P = 0.0456) and in the nasal quadrant (P = 0.032), but not in the remaining quadrants. Postoperative measurements were higher than those of PR1 in all quadrants (temporal P=0.011; superior P = 0.0098; nasal P < 0.0001; inferior P = 0.0081) and in 360 degrees average (P < 0.0001), suggesting that the presence of cataract significantly influences RNFL thickness as measured by Strains OCT. More advanced degrees of lens opacity were correlated to a higher decrease in RNFL thickness values (r = 0.4071, P = 0.0434). Conclusions: While pupil size only marginally affects RNFL measurements performed by Stratus OCT, the presence and degree of cataract seem to have a significant impact. This effect should be taken in consideration when using this technology for the diagnosis of glaucoma and other neuro-ophthalmologic disorders possibly affecting the RNFL.