Editors Selection (IGR: 12-2) | International Glaucoma Review #305

Editors Selection IGR 12-2

Clinical glaucoma: NPG - IOP

Comment by Arthur Sit on:

15103 Diurnal variation of intraocular pressure in suspected normal-tension glaucoma, Hasegawa K; Ishida K; Sawada A et al., Japanese Journal of Ophthalmology, 2006; 50: 449-454

See also comment(s) by John Liu •

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5.3% of patients had IOP above 20 mmHg at least once in one eye; many IOPs above 20 mmHg were measured outside office hours

Hasegawa et al. (1057) performed a retrospective cross-sectional study of the 24-hour IOP patterns from 569 Japanese patients with untreated normal tension glaucoma (NTG) examined between 1989 and 2003. This straight-forward, but well-designed study is by far the largest reported study of 24-hour IOP patterns in normal tension glaucoma patients. Glaucoma was defined as glaucomatous optic nerve changes and a corresponding visual field change using standard automated perimetry. IOP was measured every 2 hours by experienced physicians using Goldmann applanation tonometry in the sitting position. Nighttime pressures were assessed by awakening the patient and measuring within 5 minutes. The authors found that 5.3% of patients had IOP above 20 mmHg at least once in one eye, resulting in a reclassification as primary open angle glaucoma (POAG). Additionally, 43.4% of subjects who were reclassified as POAG had IOP above 20 mmHg outside of clinic hours. Peak and trough times were identified for 507 of the 524 patients with NTG. Peak IOP occurred outside of clinic hours for 41.4% of patients. Trough IOP occurred outside of clinic hours in 84.1% of patients.

This study highlights the variability of IOP and the limitations of periressures occur outside of office hours in a large proportion of patients and reliance on office measurements may result in inappropriate treatment.

Interestingly, only a small percentage of patients with 24-hour IOP measurements were reclassified as POAG. This suggests, as previous studies have reported, that NTG is much more common in Japan than other countries studied. The reasons for this have yet to be elucidated. Although central corneal thickness was not measured as part of this study, previous studies have reported no difference between POAG and NTG patients in Japan.¹

This study clearly demonstrates that optimal glaucoma management would involve 24-hour IOP measurement, at least periodically. We await the development of technology to enable this for all glaucoma patients.

References

Wu LL, Suzuki Y, Ideta R, Araie M. Central corneal thickness of normal tension glaucoma patients in Japan. Jpn J Ophthalmol 2000; 44: 643-647.

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