To evaluate the effect of Topcon spectral domain optical coherence tomography (OCT) image quality on macular thickness measurements and error rate in healthy subjects and patients with clinically significant diabetic macular edema (CSME).

In this prospective comparative case series, macular thickness measurements and the rate of decentration and segmentation errors were evaluated before and after reducing image quality factor (QF). To reduce the QF below 45, tetracycline eye ointment was applied on the corneal surface.

Forty eyes of 40 subjects including 18 healthy eyes and 22 eyes with CSME were included. In both groups, the difference in CST measurements before and after reducing the image QF was not statistically significant both before and after error correction (all P>0.05). The rate of decentration error was statistically similar before and after reducing image QF in normal and CSME eyes (P=0.50, P=0.69, respectively). However, the rate of segmentation error was statistically significantly higher after reducing QF both in normal and CSME eyes (P=0.008 and P=0.004, respectively). In both groups, eyes with segmentation error had higher change in image QF (both P=0.01.

Reducing image quality results in higher rate of segmentation error in normal eyes and in eyes with CSME.