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Editors Selection IGR 20-2

Computerized image analysis: HRT AND CCT

Comment by Linda Zangwill on:

16761 Central corneal thickness and correlation to optic disc size: a potential link for susceptibility to glaucoma, Pakravan M; Parsa A; Sanagou M et al., British Journal of Ophthalmology, 2007; 91: 26-28

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Interest in the relationship between central corneal thickness (CCT) and susceptibility to glaucoma has increased since the Ocular Hypertension Treatment Study first reported the independent relationship between CCT and the development of glaucoma. Evaluation has focused on the relationship between CCT and anatomical and physiological factors other than IOP, and CCT's role in the pathogenesis of glaucomatous progression. Pakravan et al. (28) investigated the possible link between CCT and Heidelberg Retina Tomograph (HRT) optic disc area measurements in 72 patients with primary open angle glaucoma, and reported that CCT was inversely correlated with disc area (r = -0.284, p = .036). After stratifying by race, the authors reported a non-significant positive correlation (r = 0.479, p = .098, n = 13) in African American eyes, a negative significant correlation among Caucasian eyes (r = -0.3, p = 0.031, n = 52), and a negative non-significant association in other races (r = -0.252, p = 0.586, n = 7). It is difficult to explain why the correlation was positive in African American eyes, and negative in Caucasian and other eyes. Differences in the direction of the correlation may be explained at least in part to a lack of generalizability of the study population due to the small sample size, and the large number of eyes excluded because of intraocular procedures and poor quality HRT images. In addition, some patients contributed two eyes to the analysis, yet the correlation between eyes was not statistically accounted for in the analysis.

It should be noted that a study not cited in the Pakravan manuscript found a different relationship. Jonas et al.¹ reported no significant correlation between disc area and central corneal thickness R²= .006, p = 0.10 among a large study of 861 white normal, ocular hypertensive and primary open angle eyes. However, when the authors looked at normal eyes only (n = 239, CCT = 570.8 microns), a positive correlation between disc area and central corneal thickness was found (p = 0.05). Given these conflicting results, additional studies, with large sample sizes of eyes of different races are needed to determine the relationship between CCT and optic disc size.

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