Pupillary dilation improves quality, reproducibility of OCT in glaucoma patients

Performing optical coherence tomography after pupillary dilation appears to produce more reproducible, higher quality images for evaluating glaucoma patients compared with scans obtained on undilated eyes, according to a study by researchers in the United Kingdom. "Acquisition of high quality OCT images was not possible without pupillary dilatation in about 25% of the patients," the authors said.

Michael Smith, MD, and colleagues examined the effects of pupillary dilation on the reliability of OCT performed using the Stratus OCT (Carl Zeiss Meditec). Investigators used the system's "fast optic disc" and "fast RNFL thickness" programs to measure the retinal nerve layers (RNFL) and optic nerve head cup-to-disc ratios in 38 glaucoma patients.

Two scans were obtained both before and after pupillary dilatation, which was achieved using tropicamide 1% drops, according to the study.

The researchers found that no images could be obtained for nine patients (23.7%) without pupillary dilation, "but after dilation examination was possible in all patients," the authors reported.

Smaller pupil sizes and increasing cataract grade were associated with the inability to obtain scans on undilated eyes, they noted.

Investigators also found that scan quality, as judged using the signal strength score, was higher for dilated scans compared with undilated scans for both RNFL thickness (P = .011) and optic nerve head cup-to-disc ratio (P = .007). In addition, dilated scans had a higher reproducibility for RNFL thickness measurements, but not for optic nerve head cup-to-disc ratio, according to the study.

"There were significant differences between the dilated and undilated examinations for three of the five RNFL thickness variables and two of the three [optic nerve head cup-to-disc ratio] categories," the authors said.

The study is published in the December issue of British Journal of Ophthalmology.