Reproducibility of Keratometric Measurements Decreases with Time after Blinking

Repeatability of Ophtha Top topography and comparison with IOL-Master and LenstarLS900 in cataract patients

AIM

To determine the repeatability of Ophtha Top topography and assess the consistency with intraocular lens (IOL)-Master and LenstarLS900 (Lenstar) in measuring corneal parameters among cataract patients.

METHODS

Totally 125 eyes were enrolled. Corneas were successively measured with Ophtha Top, IOL-Master and Lenstar at least three times. The flattest meridian power (Kf), the steepest meridian power (Ks), mean power (Km), J0 and J45 were recorded. Intra-class correlation coefficients (ICCs), the coefficient of variance (COV), within subject standard deviation (Sw), and test-retest repeatability (2.77Sw) were adopted to determine the repeatability. The 95% limit of agreement (95%LOA) and Bland-Altman plots were used to assess comparability.

RESULTS

Repeatability of Ophtha Top topography for measuring corneal parameters showed the ICCs were all above 0.93, 2.77Sw was lower than 0.31, and the COV of the Kf and Ks was lower than 0.25. The keratometric readings with Ophtha Top topography were flatter than with the IOL-Master and Lenstar devices, while the Pearson correlation coefficients were over 0.97. The J0 and J45 with Ophtha Top topography were smaller compared with Lenstar and IOL-Master, while was comparable between Lenstar and IOL-Master.

CONCLUSION

Ophtha Top topography shows excellent repeatability for measuring corneal parameters. However, differences between the Ophtha TOP topography and Lenstar, IOL-Master both in cornea curvature and the astigmatism should be noted clinically.

Diurnal variations in ocular aberrations of human eyes

PURPOSE

To investigate the diurnal variations in ocular wavefront aberrations over two consecutive days in young adult subjects.

MATERIALS AND METHODS

Measurements of both lower-order (sphero-cylindrical refractive powers) and higher-order (third and fourth-order aberration terms) ocular aberrations were collected for 30 young adult subjects at 10 different times over two consecutive days using a Hartmann-Shack aberrometer. Seventeen subjects were myopic and 13 were emmetropic. Five sets of measurements were collected each day at approximately 3 hourly intervals, with the first measurement taken at ∼9 am and the final measurement at ∼9 pm.

RESULTS

Spherical equivalent refraction (p = 0.029) and spherical aberration (p = 0.043) were both found to undergo significant diurnal variation over the two measurement days. The spherical equivalent was typically found to be at a maximum (i.e. most hyperopic) at the morning measurement, with a small myopic shift of 0.37 ± 0.15 D observed over the course of the day. The mean spherical aberration of all subjects (0.038 ± 0.048 μm) was found to be positive during the day and gradually became more negative into the evening, with a mean amplitude of change of 0.036 ± 0.02 μm. None of the other considered sphero-cylindrical refractive power components or higher-order aberrations exhibited significant diurnal variation over the two days of the experiment (p > 0.05). Except for the lower-order astigmatism at 90/180 degree (p = 0.040), there were no significant differences between myopes and emmetropes in the magnitude and timing of the observed diurnal variations (p > 0.05).

CONCLUSIONS

Significant diurnal variations in spherical equivalent and spherical aberration were consistently observed over two consecutive days of measurement. Research and clinical applications requiring precise refractive error and wavefront measurements should take these diurnal changes into account when interpreting wavefront data.

Comparison of automated and partial coherence keratometry and resulting choice of toric IOL

PURPOSE

Consistent astigmatism correction with implantation of a toric intraocular lens (IOL) requires accurate preoperative keratometry. This article compares corneal astigmatism determined by an autokeratometer (Topcon KR-7100) and a partial coherence interferometry keratometer (IOLMaster 500) and considers if any discrepancy ultimately alters in final cylindrical power of the toric IOL for implantation.

METHODS

Keratometry of 235 eyes was performed using both instruments. Corneal astigmatism was transformed into vector components J0 and J45 and cylindrical power at the IOL plane calculated. Comparisons were made using paired t test and correlation and Bland-Altman analyses.

RESULTS

Although interinstrument differences for J0 (p = 0.013), J45 (p = 0.012), and toric IOL cylindrical power (p < 0.001) were statistically significant, a high correlation for these (R = 0.96, 0.90, and 0.90, respectively) was observed. IOLMaster tended to overestimate corneal astigmatism by 0.13 (±0.31) diopters and toric IOL cylinder by 0.11 (±0.18) diopters. Difference in calculated toric IOL cylindrical power correlated poorly with corneal curvature (R = 0.007) and astigmatism (R = -0.004).

CONCLUSIONS

The two keratometers were generally concordant in measuring corneal astigmatism. However, the resultant choice of toric IOL cylinder power differed appreciably in 40% of eyes examined. Therefore, postoperative visual outcome with toric IOL implantation may be optimized by a thorough analysis of biometry data before IOL selection, paying special attention to any difference in corneal astigmatism as measured by more than one instrument.