Assessment of objective and subjective eccentric refraction.
OBJECTIVE
When performing perimetry, refracting subjects with central visual field loss, and in emmetropization studies, it is important to accurately measure peripheral refractive errors. Traditional methods for foveal refraction often give uncertain results in eccentric angles as a result of the large aberrations and the reduced retinal function. The aim of this study is therefore to compare and evaluate four methods for eccentric refraction.


METHODS
Four eccentric methods were tested on 50 healthy subjects: one novel subjective procedure, optimizing the detection contrast sensitivity with different trial lenses, and three objective ones: photorefraction with a PowerRefractor, wavefront measurements with a Hartmann-Shack sensor, and retinoscopy. The peripheral refractive error in the horizontal nasal visual field of the right eye was measured in 20 degrees and 30 degrees.


RESULTS
In general, the eccentric refraction methods compared reasonably well. However, the following differences were noted. Retinoscopy showed a significant difference from the other methods in the axis of astigmatism. In 30 degree eccentric angle, it was not possible to measure 15 of the subjects with the PowerRefractor and the instrument also tended to underestimate high myopia (<-6 D). The Hartmann-Shack sensor showed a myopic shift of approximately 0.5 D in both eccentricities. The subjective method had a relatively larger spread.


CONCLUSIONS
This study indicates that it is possible to assess the eccentric refraction with all methods. However, the Hartmann-Shack technique was found to be the most useful method. The agreement between the objective methods and the subjective eccentric refraction shows that detection contrast sensitivity in the periphery is affected by relatively small amounts of defocus.
Lundström
Linda
L
Biomedical and X-Ray Physics, Department of Physics, Royal Institute of Technology, Stockholm, Sweden. linda@biox.kth.se
Gustafsson
Jörgen
J
Svensson
Ingrid
I
Unsbo
Peter
P
D000328:Adult; D000368:Aged; D015350:Contrast Sensitivity; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation / Q000592:standards*; D005260:Female; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012029:Refraction, Ocular; D042262:Retinoscopy; D014794:Visual Fields