Photoreceptor outer segment layer thickness measured manually on images from spectral domain optical coherence tomography in healthy volunteers

BACKGROUND AND OBJECTIVE

To investigate photoreceptor outer segment layer thickness measured with a manual technique on images from spectral domain optical coherence tomography (OCT) in healthy volunteers.

MATERIALS AND METHODS

In 60 eyes of 30 healthy volunteers, a spectral domain OCT device (Spectralis, Heidelberg Engineering) was used to obtain cross-sectional images of the retina. For each volunteer, two images of each eye were obtained in one sitting. Images were digitally enlarged and the manual calipers feature of the device's software was used to measure, at the lowest point in the fovea, the thickness of the photoreceptor outer segment layer. All measurements were performed by the same investigator. Repeatability was evaluated with the Bland-Altman repeatability coefficient, and intersubject variability with Pearson's coefficient of variation.

RESULTS

The mean values of measurements across all the volunteers were as follows: right eye first image 38.1 micrometers, right eye second image 37.9 micrometers, left eye first image 37.9 micrometers, left eye second image 37.9 micrometers. The repeatability coefficient, i.e. the difference between repeated measurements which would be exceeded in only 5% of cases, was 1.6 micrometers. Coefficients of variation for the right eye were 3.4% for the first images and 3.4% for the second images, and for the left eye they were 3.2 and 4.0% respectively.

CONCLUSION

With a manual method based on spectral domain OCT, the thickness of the photoreceptor outer segment layer at the central fovea can be measured within a useful range of repeatability and appears to be relatively constant across healthy volunteers.