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Session Title: Quality of vision evaluation techniques
Session Date/Time: Tuesday 08/10/2013 | 14:00-16:00
Paper Time: 14:50
Venue: Elicium 2 (First Floor)
First Author: : M.Mrochen SWITZERLAND
Co Author(s): : J. Schneeberger J. Wernli S. Schumacher
The success and safety of a refractive surgery is still defined by subjective measures of the clinical visual acuity and therefore reliable on the patient, investigator and the surroundings. An objective measurement of the performance of the eye would be much more preferable, therefore several objective metrics were introduced by vision scientist over the last years. One promising objective metric is the Visual Strehl Ratio based on the Optical Transfer Function (VSOTF). Between the log(VSOTF) and the clinical obtained visual acuity (in logMAR) a linear relationship is reported. The VSOFT can be calculated from wavefront measurements and takes into account neural effects as well as polychromatic light. The VSOFT offers therefore the possibility to investigate objectively the outcome from standard and wavefront guided LASIK treatments.
The data of the patients was collected at several sites in the US. Data analysis was performed at IROC Science to Innovation AG, Zurich, Switzerland.
Retrospectively the data of 36 patients who had LASIK (standard or wavefront guided) was investigated. The polychromatic VSOFT at the retinal plane as well as for a defocus ranging from -5 to 5 D from the retinal plane was calculated pre- and post-operatively using a MATLAB script. The VSOFT at the retinal plane, the maximal VSOFT within the defocus range and the depth of focus defined by a VSOTF of 0.24 which correlates approximately with a clinical visual acuity of 0.8 were compared pre- and postoperatively. Analysis of subgroups between the standard and wavefront guided treatment were performed.
Pre-operatively the polychromatic VSOFT showed the expected correlation with the clinical obtained uncorrected visual acuity (UCVA) in logMAR (VA(logMAR)=-1.3*log(VSOFT)+0.06 (R2=0.63)). For all patients visual acuity could be increased by the treatment subjectively (UCVA) from VA 1.13 ± 0.38 logMAR to -0.08 ± 0.10 logMAR and objectively (VSOTF) from log(VSOFT) = -1.41± 0.62 to -0.19 ± 0.10. The comparison between the standard and wavefront guide group showed that the post-operative visual acuity subjectively (UCVA) is in average equal with -0.06 ± 0.05 logMAR in the standard and -0.08 ± 0.11 logMAR in the wavefront guided group The same accounts for the objective metric log(VSOTF) with -0.20 ± 0.03 in the standard and -0.19 ± 0.10 in the wavefront group, respectively.
The investigation shows that the pre-operative VSOFT correlates well with the clinical measured visual acuity VA and therefore is a good objective metric to evaluate the visual performance. Compared to the clinical obtained visual acuity the VSOFT is independed of secondary effects, such as light level of measurement, patients subjective feelings, examination procedure, and further surrounding influence factors. Within the number of investigated patients no difference in success of standard and wavefront guided treatment could be detected with either metric.
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