Here you find some scientific studies carried out with the PowerRef II.
“Results: In all cases, vergence and accommodation response slopes (gain) were steeper and closer to 1.0 in the expert group (p = 0.001), with the largest expert/naive differences for both vergence and accommodation being for near targets (p = 0.012). For vergence, the differences between expert and naive response slopes increased with increasingly open-loop targets (linear trend p = 0.025). Although we predicted that proximal cues would drive additional response in the experts, the proximity-only cue was the only condition that showed no statistical effect of experience.”
“Conclusion: Maximum relaxation of accommodation occurred for binocular targets receding into the distance. Proximal and disparity cues aid relaxation of accommodation to a greater extent than blur, and thus non-cycloplegic refraction targets should incorporate these cues. This is especially important in screening contexts with a brief opportunity to test for significant hyperopia. MHR (maximally hyperopic refraction) in our laboratory was found to be a reliable estimation of cycloplegic refraction.”
“Conclusion: MEM (Monocular Estimation Method) and PR (PowerRefractor) provided similar estimates of RE (Refractive Error) and of accommodative lag once the PR data were screened for inattending using an accommodative response slope criterion. Adult-like accommodative response between 3 and 12 months of age suggest that acuity at these ages is not limited by accommodative immaturity. Further, mature accommodation may attenuate RE-related defocus signals for emmetropization.”
"Results: The PowerRefractor typically read <1 D of myopia when the retinoscopy reflex was judged to be neutral at the same working distance in both infants and adults. The slopes of both infant and adult validation functions (trial lens power vs. measurement of induced defocus) were close to 1 over a 4D range. The infant slopes were significantly greater than those of the adults, however.
Conclusions: The results suggest that the instrument is capable of detecting large amounts of defocus but needs individual calibration for detailed studies of accommodative accuracy and absolute levels of defocus, as has been recommended previously for adult subjects."
"OBJECTIVE: To establish whether refraction state in children up to the age of 15 years measured by photorefraction using PowerRef II device is comparable with values measured using common methods like skiascopy and autorefractor. Photorefraction is a quick method to determine refractive state from a distance without mydriasis and simultaneously in both eyes. It appears, therefore, to be a useful tool for measuring refractive errors of infants and older noncooperative subjects. However, its accuracy and reliability has been discussed.
METHODS: In this study the authors assess accuracy of measurement of refractive errors by photorefraction in 40 children (19 boys, 21 girls) at the age ranging from 4 month to 15 years (average 4.8 years), divided according to their cooperation into two groups. The values of refraction acquired by photorefraction using PowerRef II device were compared with skiascopy in 23 noncooperative infants and with values of refraction from common autorefractor Nidek AR 600 in 17 cooperating children.
RESULTS: Comparing results of both groups we have detected an average difference 0.41 D between skiascopy and photorefraction for spherical equivalents (0.45 for spheres, 0.42 for cylinders), average difference between spherical equivalents from autorefractor and photorefractor measurements was comparable: 0.52 D (0.51 for spheres, 0.55 for cylinders).
CONCLUSION: Refractions measured by eccentric photorefraction with PowerRef II were comparable to those obtained by common methods of refraction measurement in children--i.e. skiascopy and autorefractor. Values of refraction were undervalued only in two cases of higher myopia during photorefraction measurement compared to autorefractor values. There was no significant shift by photorefraction measurement to myopic or hypermetropic values."
Cesk Slov Oftalmol. 2005 May; 61(3): 198 - 204
The infrared photorefractor PowerRef II (PR II; PlusoptiX AG, Nürnberg, Germany) uses the principle of eccentric photorefraction. In eight subjects the mean non-cycloplegic refraction measured with the "Full Scan" mode of the PR II at a far viewing distance (0.2 D) was significantly more hypermetropic by 0.6 D compared with subjective refraction. The mean accommodation differed by about this same amount between the PR II and the Canon R1 at three different viewing distances (3, 2 and 1 D). The PR II refraction at the 1 m reference distance was 0.25 D more hypermetropic compared with the subjective refraction at far (5 m); these measures were moderately correlated (r ¼ 0.7). To determine temporal changes, the "Dynamic Scan" mode was used over a 2-min period: the mean intraindividual standard deviation was 0.32 mm for pupil diameter and 0.29 D for accommodation, while the absolute measurement error of the "Dynamic Scan" was found to be <0.12 D for the accommodation data. Interindividual reliabilities were satisfactory. However, the PR II did not provide a continuous stream of data and the specified sampling frequency of 25 Hz was rarely realized.
Ophthal. Physiol. Opt. 2004 24: 520 – 527
"Conclusion: The PowerRefractor is a useful objective screening instrument and because of its remote and rapid measurement of both eyes simultaneously is able to assess the oculomotor response in a variety of unrestricted viewing conditions and patient types."
"Purpose: To evaluate the viability of the PowerRefractor as a screening tool for examining refractive errors in large samples of children.
Methods: The variability of the PowerRefractor was estimated using four patients. The refractive error was determined using cyclopentolate and tropicamide as cycloplegic agents and compared to that determined in a non-cycloplegic situation. In a second study, the data provided by the PowerRefractor were compared to results obtained by autorefractor or retinoscopy for 150 children aged from 6 months to 5 years.
Results: Variability study. Statistical analysis showed a statistically significant difference between cycloplegic and non-cycloplegic refraction for spherical and cylindrical refractive errors (p > 0.0001 in all cases). There was no significant difference between the measurement made using tropicamide and cyclopentolate (p = 0.33 and p = 0.18, respectively).
Comparison study. In 142 of 150 patients the difference between data obtained by the PowerRefractor and an autorefractor was within 1 D (spherical equivalent). However, there was a considerable difference between the data generated by the two methods in the remaining eight patients (up to 16 D).
Conclusion: The PowerRefractor proved to be a reliable tool for estimating refractive errors in young children. The apparatus is easy to handle and the simultaneous examination of both eyes makes the PowerRefractor ideal for obtaining data on reffractive errors in large samples."
