Cup-to-Disc Ratio in Patients With Idiopathic Intracranial Hypertension Is Smaller Than in Normal Subjects?

Abstract

We read with interest the article by Geddie et al (1) that might better have been titled “Cup-to-Disc Ratio in Patients With IIH and Frisén Grade 0-2 Is Smaller Than in Normal Subjects.” The authors should be commended for tackling a difficult and complicated study. There are a variety of obstacles with a study like this, but a main one is the inclusion of cases with optic disc edema. The authors state that grade 0-2 is minimal or resolved optic disc edema. Frisén Grade 2 can be mild or moderate but is usually not minimal edema. To test the hypothesis that there is no difference in the vertical cup-to-disc ratio between idiopathic intracranial hypertension (IIH) patients and normal controls, we analyzed data from our prospective study of 50 IIH patients (2). It is well known that as optic disc edema progresses, the optic cup fills in (3). So, in our analysis, we included only Frisén grade 0 papilledema. Twenty-one of our IIH patients had grade 0 optic disc edema at their final visit. The average cup size was 0.191 ± 0.14 in the right eye and 0.187 ± 0.13 in the left eye. This compares to the results of Geddie et al of 0.143 in the right eye and 0.127 in the left eye. Another issue is that differences in cup size relate to the grading process itself. This is more subjective than it appears. The grader (B.E.G.) only graded papilledema eyes. No controls were intermixed. Was the grader aware of the hypothesis being tested? If so, could this have influenced the results? It would appear necessary in a study like this for masked graders to evaluate intermixed controls and these values be used rather than controls graded by others. Another confounding factor is that it has been our experience that some swollen optic discs never completely defervesce following treatment for IIH, even when they are technically grade 0. The mechanism may be either similar to skin not returning to normal after prolonged stretching or the effect of the presence of intermittent, prolonged, mild, increased intracranial pressure. This mechanism, we believe, can also result in a smaller optic cup appearance in IIH. In our opinion, the study of Geddie et al does not adequately demonstrate that cup-to-disc ratio is smaller in IIH patients. As stated above, this is a complicated and difficult study to undertake. Ideally, one would want to grade optic disc photographs taken before the onset of IIH. Given that this is not realistic, we urge the authors to reanalyze their data set as follows: Grade a large number of intermixed normal controls with proportions intermixed to reflect racial differences in cup size. Use 3 graders masked to the diagnosis and take the mean of the measures. Limit the analysis to grade 0 optic disc edema, where the disc does not appear elevated on stereoscopic fundus photographs. If this is performed and their results are the same, we would have more confidence in their title and conclusions. Michael Wall, MD James J. Corbett, MD Department of Neurology College of Medicine, University of Iowa Iowa City, Iowa [email protected]