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Editors Selection IGR 12-1
Anatomical Structures: Corneal thickness and severity of glaucoma
Comment by James Brandt on:
51268 Differences in central corneal thickness between the paired eyes and the severity of the glaucomatous damage, Iester M; Telani S; Frezzotti P et al., Eye, 2012; 26: 1424-1430
In this very nice study by Iester and colleagues, the investigators performed a retrospective, cross-sectional study in patients at 16 glaucoma centers cooperating in the Italian Glaucoma Registry (IGR). They sought to determine if asymmetry in central corneal thickness (CCT) of a patient's two eyes correlated to asymmetric glaucoma severity. They defined glaucoma severity on the basis of both structural metrics (cup:disc ratio, CDR) and visual field indices (mean deviation, MD; pattern standard deviation, PSD). After exclusion for incomplete data, 794 patients (1,588 eyes) were available for analysis.
The authors found that almost 20% of glaucoma patients have differences in CCT > 20 µm, and the eyes with the thinner CCT have worse visual field indices and CDRs. They did not find a tight correlation between absolute inter-eye CCT difference and glaucoma severity metrics.
Eyes with the thinner CCT have worse visual field indices and CDRs
The question of whether CCT's influence as a risk factor for glaucoma derives from its known effect as a tonometry artifact versus a more fundamental biological linkage (e.g., correlation of CCT to optic nerve biomechanics) is not clarified by this study. When acting as a tonometry artifact (thinner CCT causing tonometry measures to be artifactually low), CCT can influence physician behavior. A lower measured IOP will result in less aggressive treatment whereas higher measured IOP might cause the physician to escalate treatment. Because the patients in the IGR are mostly established glaucoma patients who have been treated for a while, it is impossible to parse out cause and effect from the data presented here. If similar findings were to be described in a population of newly-diagnosed, previously untreated glaucoma patients, this would be strong evidence of an influence of CCT not related to tonometry artifact.
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