[Intra- and interindividual comparison of corneal refraction measured by IOL-Master vs. corneal topography].

BACKGROUND

Especially for the implantation of toric intraocular lenses an exact regulation of the corneal astigmatism is important.

PATIENTS AND

METHODS

60 eyes of 30 subjects with astigmatism were examined in a period of one year. The corneal refraction was measured at three different times, each examination was repeated three times, both with the IOL-Master (Fa. Zeiss, Jena) and a corneal topograph (CSO Eye Top). The results were compared intra- and interindividually. Eyes with conjunctival or corneal inflammation, dry eye syndrome or malformation of the eyelid were excluded. Data were statistically evaluated.

RESULTS

Both the amount and the axis of corneal astigmatism were significantly different for the two devices (IOL-Master and corneal topography). Intraindividually, the mean astigmatism was 1.18 D measured by the IOL-Master (median 1.0 D) and 1.07 D measured by corneal topography (median 0.88 D). This results in a dispersion about the median of 0.54% by the IOL-Master and of 0.32% by corneal topography. Intraindividually, the mean axis of astigmatism was 73 degrees measured by the IOL-Master (median 103 degrees) and 90 degrees measured by corneal topography (median 104 degrees). The dispersion about the median of axis values was 0.55% by the IOL-Master and 0.28% by corneal topography. Use of the Wilcoxon test results in a dispersion of values of less than 2% probability value for both the amount and the axis of corneal astigmatism (p < 0.1).

CONCLUSIONS

Values measured by the IOL-Master show a wider distribution than values measured by corneal topography. The statistical spread was significant, although it was less than 3% for both intra- and interindividual measurements by the two devices. Although the median is almost equal for measurements by the IOL-Master and corneal topography, dispersion about the median is almost twice as high for intraindividual measurements by the IOL-Master. Therefore, the accuracy of measurements conducted with corneal topography is significantly higher as compared to the IOL-Master.