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Editors Selection IGR 9-4
Intraocular Pressure: CCT and severity of NTG
Comment by James Brandt on:
25121 Corneal thickness measurements in normal-tension glaucoma workups: is it worth the effort?, Kurtz S; Haber I; Kesler A, Journal of Glaucoma, 2010; 19: 58-60
Pachymetry of glaucoma patients is now commonplace. Most ophthalmologists focus their attention on glaucoma suspects and ocular hypertensives, for which data supporting the role of thinner CCT as a risk factor is strongest. Whether pachymetry is useful or necessary in patients with established POAG or normal-tension glaucoma (NTG) is less clear.
Among patients with NTG, investigators have long noted individuals with very thin corneas. Ehlers first reported this in 1974 (Acta Ophthalmol 52:740-6) and subsequent reports generally support the idea that as a diagnostic group, patients with NTG have thinner corneas. Whether or not NTG is a disease or phenotype distinct from POAG or simply one end of a wide spectrum of disease, is controversial. Although certain clinical findings (e.g., disc hemorrhages, Raynaud's phenomenon, dense para-central visual field defects) are more common among patients with NTG, these findings are also seen in patients with more typical POAG. Thin CCTs fit a similar pattern. Kurtz et al. (272) asked whether it is worth the effort to acquire CCT measurements in patients with NTG. Their retrospective review of 68 patients with carefully-defined NTG revealed a strong inverse correlation between CCT and disease severity as defined by appropriate visual field indices.
Patients with thin corneas must be watched more carefully
The relationship between CCT and glaucoma is complex ‐ the primary question is whether or not the relationship is one of a tonometry artifact or a true biological relationship. In the case of tonometry artifact, does a thin cornea result in lower IOP estimates and therefore under-appreciation of risk and less aggressive treatment by the ophthalmologist? If a true biological relationship exists, do the thinner corneas noted in many NTG patients correlate to an optic nerve head more susceptible to damage at lower IOPs? Studies like this will never resolve the question of how CCT influences disease (it is my opinion that both influences are in play), but it is clear that many patients have thin corneas and must be watched more carefully. The authors' study adds further support to the recommendation that everyone with glaucoma should have pachymetry as part of their workup.
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