To evaluate the effect of instrument aging on optical coherence tomography (OCT) measurements.

Single eyes of 60 healthy participants (60 eyes) aged 20-30 years were examined twice using a 5-year-old OCT instrument and a new OCT instrument (Carl Zeiss Meditec, Dublin, CA, USA). The measurements and changes in signal strength were investigated using both instruments.

The signal strengths of the new and aged instruments were 8.6 ± 0.8 and 5.0 ± 1.0, respectively, which was a statistically significant difference ( p < 0.001). In addition, the central macular thicknesses (CMT) of the new and aged instruments were 201.1 ± 16.1 µm and 210.3 ± 16.0 µm, respectively. The thickness was significantly greater using the aged instrument ( p < 0.001). Repeated measurements within the same eye were compared, and the difference in CMT was 3.2 using the new instrument and 10.5 using the aged instrument ( p < 0.05). The intraclass correlation coefficient (ICC) was compared to evaluate the reproducibility of each instrument. The ICC values of nine areas of Early Treatment Diabetic Retinopathy Study in the aged instrument were 0.371-0.872, indicating low reproducibility. However, the new instrument showed high reproducibility with values of 0.806-0.947.

Higher signal strength and lower CMT were observed using the new instrument compared to the aged instrument. Additionally, there were no differences in signal strength errors between the instruments. However, the error in CMT measured using the new instrument was significantly smaller compared to that using the aged instrument. Therefore, the effect of instrument aging should be accounted for in analyses of OCT measurements.