Clinical evaluation of automated refraction in anterior chamber pseudophakia

Automated and subjective refraction with monofocal, multifocal, and EDOF intraocular lenses: review

Automated refraction (Scheiner principle) is universally used to start a visual examination. Although the results are reliable in eyes implanted with monofocal intraocular lenses (IOLs), they may be less precise with multifocal (mIOL) or extended depth-of-focus (EDOF) IOLs and can even indicate a refractive error that does not clinically exist. Autorefractor results with monofocal, multifocal, and EDOF IOLs were investigated through literature search analyzing the papers reporting the difference between automated and clinical refraction. The average difference ranged between -0.50 diopter (D) and -1.00 D with most mIOL and EDOF IOLs. The differences in astigmatism were generally much lower. Autorefractors using infrared light cannot measure eyes with high technology IOLs precisely because of the influence of the refractive or of the diffractive near add. The systematic error induced with some IOLs should be mentioned in the IOL label to prevent possible inappropriate refractive procedures to treat apparent myopia.

Validity of autorefraction after cataract surgery with multifocal ReZoom intraocular lens implantation

PURPOSE

To evaluate the clinical utility of spherocylindrical automated refraction (AR) compared with subjective manifest refraction (MR) after cataract surgery with implantation of ReZoom refractive multifocal intraocular lenses (IOLs) (Advanced Medical Optics, Inc.).

SETTING

Private Practice.

METHODS

This prospective nonrandomized interventional study consisted of 72 patients with bilateral cataract and a potential visual acuity of at least 20/40. Patients had bilateral nonsimultaneous cataract surgery and implantation of a ReZoom IOL. Manifest refraction was performed in all patients followed by 3 consecutive measurements using the Topcon KR-8000 autorefractor with nondilated and dilated pupils. Assessment of repeatability of multiple consecutive ARs and comparison of the AR and MR using power vector analysis were performed at the 6-month follow-up. The main outcome measures were the correlation between AR and MR with sphere, spherical equivalent, and astigmatism as well as the repeatability of AR before and after dilation with phenylephrine 10%.

RESULTS

Repeatability analysis showed that the initial nondilated AR was not significantly different from the mean of the 3 refractions for nondilated and dilated measurements. The mean difference between the initial AR and the MR was -0.84 +/- 0.62 diopters (D) for sphere (SD), -1.00 +/- 0.61 D for spherical equivalent, and -0.06 +/- 0.19 D and -0.01 +/- 0.17 D, respectively, for J(0) and J(45), the 2 components of astigmatism. Linear regression of AR versus MR data showed poor correlation for sphere (R(2) = 0.4852) and spherical equivalent (R(2) = 0.5529), whereas the correlation for the 2 astigmatic components of vector analysis was excellent (J(0), R(2) = 0.8881; J(45), R(2) = 0.8640). Correlation was better when the MR residual refractive defect was higher.

CONCLUSIONS

Although autorefraction showed excellent agreement with subjective refractive astigmatism, correlation with spherical values was poor, with a trend toward more negative values. Autorefraction after ReZoom IOL implantation can be used as a good starting point for subjective refraction of astigmatism; however, spherical values should be underestimated.

Clinical evaluation of infrared autorefractors for use in contact lens over refraction

We examined the ability of autorefractors to provide an accurate means of contact lens over-refraction measurement. Over-refraction measures, performed using six commercially available automated infrared autorefractors and retinoscopy, were compared with subjective refraction. A total of 40 contact lens wearers (20 soft lens wearers and 20 rigid gas permeable (RGP) lens wearers) participated in the study. All six autorefractors were able to provide over-refraction measures in all subjects. Data analysis revealed differences in autorefractor performance between the two types of contact lens wearer with greater accuracy and lower variability being found in the soft lens wearing subjects compared with the RGP group. The level of agreement between retinoscopy and subjective over-refraction results was lower in soft lens wear and higher in RGP wear than the levels found between the autorefractor and subjective over-refraction measures. We conclude that autorefractors provide a useful means of measuring contact lens over-refraction in soft lens wearers. Over-refraction results should be treated more cautiously in RGP wearers.

Clinical evaluation of the Allergan Humphrey 500 autorefractor and the Nidek AR-1000 autorefractor

AIMS/BACKGROUND

The intentions of this study were to estimate agreement between two different autorefractors and standard subjective refraction techniques and to evaluate the clinical implications of relying on the autorefractor measurements.

METHODS

Subjective refraction was carried out on 448 cycloplegic eyes and compared with cycloplegic readings with the Allergan Humphrey 500 autorefractor (448 eyes) and the Nidek AR-1000 autorefractor (160 eyes). Each refraction was followed by clinical visual acuity measurement. The study population comprised 224 healthy students, 107 men and 117 women, with a mean age of 20.6 (SD 1.1) years.

RESULTS

Both the Nidek and Humphrey autorefractors measured more negative or less positive refractive values compared with subjective refraction and these biases were statistically significant (Humphrey right eye -0.23 D, p = 0.0001, left eye -0.20 D, p = 0.0001), (Nidek right eye -0.13 D, p = 0.0001, left eye -0.11 D, p = 0.0002). Comparing the results of autorefraction with subjective refraction, the Nidek was better than the Humphrey autorefractor in several ways: a smaller mean difference, better agreement between spherical equivalent values, narrower limits of agreements, and better visual acuity obtained with the autorefraction. On the other hand, the Humphrey autorefractor agreed better with subjective refraction concerning cylinder axis.

CONCLUSION

The results show that both autorefractors represent a valuable complement to subjective refraction, but cannot be used as a replacement.

Comparative evaluation of the Allergan Humphrey 570 and Canon RK-1 autorefractors: II. Objective autorefraction in pseudophakes

Fifty patients (50 eyes) with posterior chamber intraocular lenses and a best corrected visual acuity of at least 6/12 were studied. The Allergan-Humphrey 570 (AH-570) and Canon RK-1 autorefractors were compared in terms of ease of operation, time taken and their accuracy relative to clinical refraction. Both the autorefractors were equally easy to operate but the AH-570 was quicker. The AH-570 had a higher percentage of eyes within 11 degrees of clinically determined cylinder axis while the Canon RK-1 had a higher percentage of patients within 0.51 diopters of spherical equivalence, sphere power and cylinder power as determined by clinical refraction. This difference in the accuracy of objective autorefraction was not statistically significant; the clinical significance is uncertain.

Comparative evaluation of the Allergan Humphrey 570 and Canon RK-1 autorefractors: I. Objective autorefraction in normal subjects

Fifty normal subjects were studied comparing objective autorefraction using the Allergan Humphrey 570 (AH 570) and Canon RK-1 autorefractors in terms of ease of operation, the time taken and their accuracy compared with clinical refraction. Both the autorefractors were equally easy to operate but the AH 570 was quicker. Objective autorefraction with the AH 570 was more accurate than using the Canon RK-1 especially with respect to spherical equivalence, sphere power and cyclinder axis: approximately 80% of the values were within 0.51 dioptres or 11 degrees of clinical refraction compared to approximately 60% for the Canon RK-1. The possible reasons for the superior performance of the AH 570 are discussed.