December 2010
Volume 51, Issue 12
Free
Letters to the Editor  |   December 2010
Author Response: Metamorphopsia Assessment before and after Vitrectomy for Macular Hole
Author Affiliations & Notes
  • Kristian Krøyer
    Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Denmark; and
  • Ulrik Christensen
    Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Denmark; and
  • Morten la Cour
    Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Denmark; and
  • Michael Larsen
    Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Denmark; and
    the National Eye Clinic, Kennedy Center, Copenhagen, Denmark.
Investigative Ophthalmology & Visual Science December 2010, Vol.51, 6896. doi:10.1167/iovs.10-6082
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      Kristian Krøyer, Ulrik Christensen, Morten la Cour, Michael Larsen; Author Response: Metamorphopsia Assessment before and after Vitrectomy for Macular Hole. Invest. Ophthalmol. Vis. Sci. 2010;51(12):6896. doi: 10.1167/iovs.10-6082.

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      © ARVO (1962-2015); The Authors (2016-present)

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Dave and Narayanan address the need to clarify a few points in our article, “Metamorphopsia Assessment before and after Vitrectomy for Macular Hole,” 1 in which we described the quantification of metamorphopsia in a subset of patients included in the Copenhagen Macular Hole Study, a randomized clinical trial (RCT) comparing different methods of surgical treatment for macular hole. 
Dave and Narayanan correctly note that the number of patients enrolled in the RCT was 78, whereas only 55 patients were enrolled in the study describing our novel method of metamorphopsia assessment. In the study of metamorphopsia, 23 patients were excluded because they did not fulfill the inclusion criteria or were unable to complete the test for one of the following reasons: bilateral macular hole or lamellar hole at baseline (n = 12), anisometropia greater than 3 D (n = 3), amblyopia in the fellow eye (n = 1), or inability to complete the test, most commonly because of excessive phoria or exclusive eye dominance (n = 7). 
In the group of patient who did not show any change in metamorphopsia after hole closure (n = 4), two had undergone reoperation to close the hole. Another six patients experienced metamorphopsia reduction despite having had two operations. 
Dave and Narayanan address the need to validate the test–retest variability of our method. We determined variability by examining patients twice at baseline with a short interval between each test. Calculating the Pearson's correlation coefficient between the two sets of responses showed a correlation coefficient of 0.71 (P < 0.001). 
Dave and Narayanan suggest that the Wilcoxon signed-rank test would be more appropriate for comparing pre- and postoperative metamorphopsia, because the groups under comparison are dependent and cannot be assumed to be normally distributed. We believe that this argument is valid, and consequently we have made the same comparison using the Wilcoxon signed rank test which also shows a significant difference between pre- and postoperative metamorphopsia for all the tested eccentricities (P < 0.001). Means and standard deviations of the metamorphopsia measure before and after surgery are presented graphically in our Figure 1, “Metamorphopsia before and after surgery.” 
We used the one-way ANOVA test to compare metamorphopsia before and after surgery. Our data were nonparametric but expressed homogeneity of variance. However, we believe that Dave and Narayanan are correct when arguing that the Kruskal-Wallis one-way analysis of variance may be more appropriate for nonparametric data. Analyzing the effect of eccentricity on metamorphopsia using the Kruskal-Wallis test, however, does not alter our results or our conclusions. 
In the Results section, a reference is made to Figure 2 regarding the effect of eccentricity on the degree of metamorphopsia reduction after surgery. The reference should have been made to Figure 3. 
References
Krøyer K Christensen U la Cour M Larsen M . Metamorphopsia assessment before and after vitrectomy for macular hole. Invest Ophthalmol Vis Sci. 2009;50(12):5511–5515. [CrossRef] [PubMed]
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