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Editors Selection IGR 9-4
Clinical examination methods: Progression and CCT
Comment by Felipe Medeiros on:
12415 Central corneal thickness and progression of the visual field and optic disc in glaucoma, Chauhan BC; Hutchison DM; Leblanc RP et al., British Journal of Ophthalmology, 2005; 89: 1008-1012
Following the increased attention directed to the role of corneal thickness in glaucoma management and its possible role as a surrogate for posterior scleral/lamina cribrosa thickness, Chauhan et al. (541) evaluated whether central corneal thickness (CCT) was a risk factor for progression in patients with established disease. The authors reported the results on a relatively small, but carefully followed cohort of 54 patients (101 eyes) who had been tested with confocal scanning laser ophthalmoscopy (HRT, Heidelberg Retina Tomograph) and standard automated perimetry every 6 months for an average follow-up time of 9.2 years. The visual field and optic disc data were analyzed for progression using a trend algorithm called Evidence of Change (EOC), developed by the authors. For the visual fields, the EOC depends on the significance of the regression of the mean pointwise pattern deviation value over follow-up, whereas for the optic disc, the EOC scores were based on the regression of sectoral neuroretinal rim area values over time.
No correlation was found between CCT and progressionFor both analyses, higher EOC scores, ranging from 0 to 20, indicate more progression. Although the average EOC score in the groups with thinner corneas tended to be higher than in the groups with thicker corneas, no statistically significant correlation was observed between CCT and EOC values. When visual fields were analyzed for progression using the Glaucoma Change Probability algorithm, there was a tendency for the progressing patients to have lower CCT than the non-progressing ones, but again the differences were not statistically significant.
The results of Chauhan et al. contrast with those from three other studies, including the Ocular Hypertension Treatment Study (OHTS), which have also identified CCT as a risk factor for development or progression of glaucoma.1-3 It is possible that some of the non-significant results presented by Chauhan et al. were due to the relatively small number of patients included in their study. Also, it was not clear how the different follow-up times of the patients were taken into account in the analyses. On the other hand, results from the Early Manifest Glaucoma Treatment Trial (EMGT)4 were similar to those of Chauhan et al., in that CCT was also not identified as a risk factor for progression in patients with established disease. Different characteristics of the populations and different methodologies employed in these studies could possibly be explanations for the conflicting results. Although CCT seems to be an important factor in the assessment of glaucoma suspect patients, its role in the management of patients with established disease still needs further evaluation.
References
- Medeiros FA, Sample PA, Zangwill LM, Bowd C, Aihara M, Weinreb RN. Corneal thickness as a risk factor for visual field loss in patients with preperimetric glaucomatous optic neuropathy. Am J Ophthalmol 2003;136:805-13.
- Kim JW, Chen PP. Central corneal pachymetry and visual field progression in patients with open-angle glaucoma. Ophthalmology 2004;111:2126-32.
- Gordon MO, Beiser JA, Brandt JD, et al. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol 2002;120:714-20; discussion 829-30.
- Leske MC, Heijl A, Hussein M, Bengtsson B, Hyman L, Komaroff E. Factors for glaucoma progression and the effect of treatment: the early manifest glaucoma trial. Arch Ophthalmol 2003;121:48-56.
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