Purpose: To evaluate the impact that the pupil size and the crystalline lens opacification have on optical coherence tomography (OCT) accuracy and the necessity of pupil dilation for the examination of the nerve retinal fibber layer and the macula. Methods: One hundred fifty six eyes of 156 patients separated in two distinct groups, were examined with OCT (Stratus 3000), before and after pharmacological mydriasis. The first group consists of 78 patients with clear optical media while the second

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... consists of 78 patients with lens opacification according the Lens Opacities Classification System III (LOCS III). The fast RNFL thickness protocol was used to evaluate RNFL thickness and the fast macular scan pattern thickness for the macula thickness and volume. Results: No significant statistically differences were found between the pupil size, the quality of the signal (P>10%) and also between the pupil size and all of the parameters examined, of both groups (P>10%). Instead the signal quality was found significant different before and after mydriasis (P<0,001) without influence on the measurements accuracy. Conclusion: Pupil dilatation increases the signal strength of the examination but has no impact on