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Effect of pupillary dilatation on glaucoma assessments using optical coherence tomography

¹ Ophthalmology Department, Torbay Hospital, Torquay, Devon, UK
² Peninsula Medical School, Devon, UK
³ School of Mathematics and Statistics, University of Plymouth, UK

Correspondence to:
Michael Smith, Ophthalmology Department, Torbay Hospital, Torquay, Devon TQ2 7AA, UK; smith{at}mic73.freeserve.co.uk

Aims: To examine the effect of pupillary dilatation on the reliability of retinal nerve fibre layer (RNFL) and optic nerve head (ONH) assessments using Stratus OCT in a glaucoma clinic.

Methods: Observational study of 38 patients attending a glaucoma clinic. The "fast optic disc" and "fast RNFL thickness" programs on Stratus OCT were used to measure the RNFL thickness and ONH cup to disc ratio (CDR). Two scans were done before dilatation and two after dilatation with tropicamide 1% drops. The mean values and reproducibility before and after dilatation were compared, along with the quality of scans as indicated by the "signal strength" score.

Results: In nine patients (23.7%) no images were obtained undilated but after dilatation examination was possible in all patients. Inability to obtain an undilated scan was associated with smaller pupil size and increasing cataract. The scan quality, as judged by the signal strength score, was higher dilated than undilated for both RNFL thickness (p = 0.011) and ONH CDR (p = 0.007). Reproducibility was higher with dilated scans for RNFL thickness but not for ONH CDR. There were significant differences between the dilated and undilated examinations for three of the five RNFL thickness variables and two of the three ONH CDR categories.

Conclusions: Acquisition of high quality OCT images was not possible without pupillary dilatation in about 25% of the patients. The dilated scans were more reproducible and of higher quality than the undilated scans. The two methods of examination do not appear to be interchangeable, suggesting that in follow up examinations the pupil should be in the same condition as at baseline. Pupillary dilatation is recommended before glaucoma assessments using Stratus OCT.

Abbreviations: CDR, cup to disc ratio; LOCS, lens opacities classification system; OCT, optical coherence tomography; ONH, optic nerve head; RNFL, retinal nerve fibre layer

Keywords: optical coherence tomography; glaucoma; ocular hypertension

Competing interests: None declared.

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