Intra-observer repeatability of optical quality measures provided by a double-pass system

The aim was to evaluate the intra-observer repeatability of the ocular optical quality measurements provided by a double-pass system in healthy eyes.

A total of 24 healthy eyes of 24 patients with ages ranging from 20 to 60 years were included in the study. Three consecutive measurements were obtained by an experienced examiner with the Optical Quality Assessment System (Visiometrics) of the following parameters defined by the manufacturer as follows: cut-off spatial frequency for the modulation transfer function (COMTF), Strehl ratio, width of the point spread function (PSF) at 10 per cent of its maximal height (PSF10) and width of the PSF at 50 per cent of its maximal height (PSF50). Intra-observer repeatability for 3.0 mm pupil measurements was evaluated by the within-subject standard deviation (S(w) ) and intra-class correlation coefficient (ICC).

The S(w) values for the different parameters evaluated were 4.34 cycles per degree for COMTF, 0.03 for the Strehl ratio, 1.14 arcmin for PSF10 and 0.36 arcmin for PSF50. The ICC values for these parameters were 0.746, 0.627, 0.783 and 0.814 for COMTF, Strehl ratio, PSF10 and PSF50, respectively. Statistically significant correlations were found between COMTF and the S(w) for PSF50 (r = -0.45, p = 0.03), and between the S(w) and the mean value for PSF50 (r = 0.42, p = 0.04). The significance of these correlations would vanish when considering the Bonferroni correction.

Measurements provided by the Optical Quality Assessment System should be considered and interpreted with caution because their consistency seems to be limited, especially in eyes with poor optical quality. The limitation in the validity of measurements due to the use of infrared light instead of middle-wavelength light should also be considered.