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Editors Selection IGR 12-1
Intraocular pressure: CCT
Comment by James Brandt on:
16857 Central corneal thickness and visual field progression in patients with chronic primary angle-closure glaucoma with low intraocular pressure, Hong S; Kim CY; Seong GJ et al., American Journal of Ophthalmology, 2007; 143: 362-363
16860 Central corneal thickness and visual field loss in fellow eyes of patients with open-angle glaucoma, Rogers DL; Cantor RN; Catoira Y et al., American Journal of Ophthalmology, 2007; 143: 159-161
Ever since the Ocular Hypertension Treatment Study (OHTS) showed that central corneal thickness (CCT) is a potent predictive factor for the development of glaucoma, it has become widely accepted that CCT plays an important role in risk assessment of glaucoma suspects and ocular hypertensives.
Rogers et al.(29) performed a retrospective review of patients with glaucoma in whom bilateral CCT measurements were performed within one month of bilateral visual field testing. They compared inter-eye differences in CCT, mean deviation (MD) and pattern standard deviation (PSD)by subtracting left eye values from the right eye values, finding that worse visual field changes occur in the eye with the thinner cornea. IOP data is not provided.
Hong et al. (26) performed a retrospective review of patients with chronic primary angle-closure glaucoma (PACG) who had been successfully treated for the disease and had sustained IOPs below 18 mmHg. They split their cohort of 163 eyes into two evenly-divided groups (< 540 µm and 7 ≥ 540 μm) and evaluated visual field progression. There was no difference in baseline IOP or MD, but after 3 years of follow-up, MD had deteriorated more in the thin cornea group than in the group with thicker corneas. Although IOPs were virtually identical in the two groups at three years, we are not told whether these IOPs are treated or not and what difference, if any, exists between the medication burden for each group to achieve the same IOPs. Unfortunately, both papers suffer from similar limitations - Rogers et al. present a cross-sectional snapshot of the relationship between CCT and visual field, but without IOP and treatment data we do not know whether the eye(s) with thinner corneas were less aggressively treated by their ophthalmologists. Similarly, although Hong and co-workers provide a longitudinal picture of the relationship between CCT and visual field progression, we do not know whether the physicians treating this cohort of patients were more or less aggressive in IOP management based on a tonometry artifact. Whether CCT is exerting its influence solely as a confounder of tonometry or is linked at a more fundamental level to the underlying pathophysiology of glaucoma, remains unknown.Finding a relationship between CCT and glaucoma progression independent of IOP in patients with established disease would support such a relationship. These two papers each hint at, but do not yet prove, such a relationship.
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