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Editors Selection IGR 24-1

Clinical examination methods: One CCT-measurement is not enough

Leon Herndon

Comment by Leon Herndon on:

13119 Central corneal thickness measurement in clinical practice, Shildkrot Y; Liebmann JM; Fabijanczyk B et al., Journal of Glaucoma, 2005; 14: 331-336


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Shildkrot et al. (769) wanted to determine if a single measurement of central corneal thickness (CCT) is an adequate sample to aid in glaucoma risk assessment in clinical practice. CCT was measured by ultrasound pachymetry on two separate occasions at least one month apart for a mean inter-test period of 276 days. Ninety-eight eyes of 98 patients were enrolled. No significant difference in mean CCT was observed between the two visits (549 µm vs 548 µm), however, measured CCT values differed by more than 20 µm in 20 eyes (20%), whereas CCT difference of at least 40 µm was seen in five eyes. There were some limitations in this study. The use of contact lenses was permitted, and there was a mix of glaucoma diagnoses and even patients without glaucoma were permitted. Fourteen patients were contact lens wearers, and ANOVA demonstrated a relationship between the difference in CCT and a history of contact lens wear. Those eyes that had a history of contact lens wear had a predilection to thinning of the cornea (-9.78 µm vs -0.09 µm in the non-wearers). The use of glaucoma medications was permitted, although there was no subgroup analysis of those on different medications. Inoue et al.1 showed that topical dorzolamide treatment increases CCT without affecting corneal endothelial morphology, and Viestenz et al.2 showed that topical prostaglandins reduce CCT significantly.

The authors conclude that a single measurement of CCT may no longer suffice for the long-term and recommend that these measurements be repeated at least once to enhance the confidence that the true CCT value is obtained. We have presented data of the CCT change over an eight-year period of time, and would agree that one measurement of CCT in a patient's lifetime is probably not adequate.3.

References

  1. Inoue K, et al. Influence of dorzolamide on corneal endothelium. Jpn J Ophthalmol 2003; 47: 129-133.
  2. Viestenz A, et al. Impact of prostaglandin-F(2 alpha)-analogues and carbonic anhydrase inhibitors on central corneal thickness - a cross-sectional study on 403 eyes. Klin Monatsbl Augenheilkd 2004; 221: 753-756.
  3. Weizer JS, Stinnett SS, Herndon LW. Longitudinal changes in central corneal thickness and their relationship to glaucoma status: an eight-year follow-up study. B J Ophthalmol. (Submitted.)


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