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 Table of Contents  
LETTER
Year : 2015  |  Volume : 10  |  Issue : 4  |  Page : 498-501

Single session, intra-observer repeatability of an advanced new generation Hartmann-Shack Aberrometer in refractive surgery candidates


1 Department of Cornea and Refractive Surgery, NMC Eye Care, New Medical Center Specialty Hospital, Abu Dhabi, United Arab Emirates
2 Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China

Date of Submission16-Jun-2015
Date of Acceptance12-Dec-2015
Date of Web Publication18-Feb-2016

Correspondence Address:
Gaurav Prakash
Department of Cornea and Refractive Surgery, NMC Eye Care, New Medical Center Specialty Hospital, Abu Dhabi
United Arab Emirates
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2008-322X.176893

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How to cite this article:
Prakash G, Jhanji V, Srivastava D, Suhail M, Rong SS, Bacero R, Philip R. Single session, intra-observer repeatability of an advanced new generation Hartmann-Shack Aberrometer in refractive surgery candidates. J Ophthalmic Vis Res 2015;10:498-501

How to cite this URL:
Prakash G, Jhanji V, Srivastava D, Suhail M, Rong SS, Bacero R, Philip R. Single session, intra-observer repeatability of an advanced new generation Hartmann-Shack Aberrometer in refractive surgery candidates. J Ophthalmic Vis Res [serial online] 2015 [cited 2018 Dec 14];10:498-501. Available from: http://www.jovr.org/text.asp?2015/10/4/498/176893

Sir,

Recently, a new aberrometer, the iDesign advanced Wavescan studio (Abbott Medical Optics, Santa Ana, CA, USA) has been launched for commercial use. This device is considered as a new, upgraded and more sensitive version of the Wavescan aberrometer (Abbott Medical Optics, Santa Ana, CA, USA). It has five times greater resolution, encompassing over 1,250 data points through a 7.0-mm pupil as compared to 240 points for the Wavescan.[1] However, it remains to be seen if this increase in sensitivity would hamper instrument repeatability by picking up extra signal noise, especially during testing of wavefront aberrations, which are variable to some extent.

In this consecutive case series, we measured the single user, single session repeatability of wavefront and other anterior segment measurements by iDesign in 100 refractive surgery candidates with no ocular morbidity except for refractive errors.

The study had institutional review board approval and followed all tenets of the Declaration of Helsinki. Informed consent was obtained from all candidates.

All candidates underwent a detailed evaluation and those with topographically evident keratoconus, dry eye, any previous surgical intervention in the eye or corneal scars/irregularity were excluded.

All measurements were obtained by a single experienced user (DS) on the iDesign aberrometer. The candidates waited in the dedicated examination room for 30 minutes with eyes closed and the room lights shut off. Then the tests were carried out in dark room conditions. A five-minute rest with the eyes closed was given between each measurement. The data is then analyzed by the instrument software, which looks for usable iris registration, wavefront data, and corneal topography data. The review screen shows a green icon for all these three data when measurements are practical for treatment or analysis. Three such consecutive 'good' measurements were taken. The right eyes were used for analysis. The data were noted and analyzed for a 6-mm pupil diameter. Even though the machine provides output till 6th order aberrations for individual polynomials, the analysis was limited up to the 4th order to maintain clinical relevance and ease of interpretation as beyond 4th order, most values were exceedingly low. Polar Zernike coefficients were used for the study. All data was then transferred as jpeg images and manually entered into an MS Excel (Microsoft, Richmond, VA, USA) sheet. The data was then transferred to SPSS software version 16.0 (SPSS Inc., Chicago, IL, USA) for analysis.

Mean and standard deviation of data for the three measurements (of 100 eyes) as well as the pooled data (n = 300) were derived. Analysis of variance was used to evaluate differences among the three measurements. The intra-subject variation was assessed by the parameters described by Altman and Bland, including intra-subject standard deviation (Sw) of the three consecutive measurements, intra-subject precision (1.96 × Sw) and intra-subject repeatability (2.77 × Sw).[2]

The means, standard deviations, 95% confidence intervals of means and the range of data are detailed in [Table 1]. Mean values for measurement in the three groups were comparable (ANOVA P > 0.05 for all measurements, [Table 1]). Intra-subject standard deviation (Sw), repeatability and precision values are presented in [Table 2]. The intraobserver Sw was 0.25 diopter (D) for sphere and 0.08 D for cylinder. The intraobserver Sw was less than 0.07 for all higher order aberration (HOA) terms. Intrasubject variation in the precision and repeatability were dependent on Sw and therefore showed similar trends [Table 2]. Coefficients of intra-subject variation (CoVar) were worst for spherical aberration [Table 2]. Sphere and cylinder had good, low CoVar values [Table 2].
Table 1. The means, standard deviation, 95% confidence interval of means and the range of data

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Table 2. Measures of repeatability for all the parameters analyzed for the new aberrometer

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Wavefront aberrometry is a sensitive tool and intra-user repeatability is an important step in the assessment of the device. Intra-subject standard deviation was low for lower order terms and 95% of the data was computed to be within 0.5 D for sphere, 0.15 D for cylinder and 3.25 degrees of each other. Wang et al also noted that the standard deviation for Wavescan was 0.29 D for sphere and 0.16D for cylinder.[3] Mean spherical equivalent (SEQ) in their study was lower (-2.86 D for virgin corneas and -0.27 D for post excimer laser corneas) as compared to our mean SEQ(-4.2 D). However, the intraclass correlations in our study were better for iDesign as compared to the Wavescan data from the previous study. For iDesign, sphere and cylinder were 0.999 and 0.995 D, as compared to 0.992 and 0.902 D, respectively, by Wavescan. This is perhaps on expected lines, as iDesign is claimed to be a more advanced version of the Wavescan.[1]

López-Miguelet al evaluated the repeatability of Topcon KR-1W for 75 eyes.[4] The 95% data for Sw was 0.40 D for spherical error and 0.26 D for astigmatism in their study. The intraclass correlation coefficients (ICCs) for auto-refraction limits of agreement (LOA) terms were not provided in the study. For wavefront data, the ICC for total ocular HOA root mean square (HOARMS) was 0.902 at 6.0 mm pupil with Topcon KR-1W.[4] In another study, López-Miguel et al evaluated the Zywave aberrometer (Bausch and Lomb, Rochester, NY, USA).[5] The ICC for total HOA and HOARMS was 0.99 and 0.96, respectively, for Zywave at 6.0 mm pupil.

Compared to the aforesaid studies, our findings revealed an ICC of 0.995 for total ocular RMS and 0.919 for ocular HOARMS at 6.0 mm pupil for the iDesign. Even though these studies were performed on different populations, the ICC values being tighter for iDesign provide a perspective towards good repeatability with iDesign.

There are certain shortcomings in the present study. The non-comparative nature of the study, and the fact that we have not compared our data to Wavescan limit interpretation of our results. However, on its own, this study establishes that the iDesign demonstrates good performance in terms of single session, intra user repeatability for anatomical, refractive and wavefront parameters and seems to be better in some aspects as compared to its predecessor, the Wavescan. A future study comparing Wavescan and iDesign head to head will be advantageous.

Financial Support and Sponsorship

Nil.

Conflicts of Interest

There are no conflicts of interest.

 
  References Top

1.
Coleman SC. High-definition Wavefront: 5X Resolution. Available from: http://www.eyeworld.org/ewsupplementarticle.php?id=281. [Last accessed on 2015 Feb 22].  Back to cited text no. 1
    
2.
Bland JM, Altman DG. Measurement error and correlation coefficients. BMJ 1996;313:41-42.  Back to cited text no. 2
    
3.
Wang L, Wang N, Koch DD. Evaluation of refractive error measurements of the wavescan wavefront system and the tracey wavefront aberrometer. J Cataract Refract Surg 2003;29:970-979.  Back to cited text no. 3
    
4.
López-Miguel A, Martínez-Almeida L, González-García MJ, Coco-Martín MB, Sobrado-Calvo P, Maldonado MJ. Precision of higher-order aberration measurements with a new placido-disk topographer and Hartmann-Shack wavefront sensor. J Cataract Refract Surg 2013;39:242-249.  Back to cited text no. 4
    
5.
López-Miguel A, Maldonado MJ, Belzunce A, Barrio-Barrio J, Coco-Martín MB, Nieto JC. Precision of a commercial hartmann-shack aberrometer: Limits of total wavefront laser vision correction. Am J Ophthalmol 2012;154:799-807.e5.  Back to cited text no. 5
    



 
 
    Tables

  [Table 1], [Table 2]


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