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Editors Selection IGR 21-1

Intraocular Pressure: IOP fluctuation and progression

Comment by Kouros Nouri-Mahdavi on:

19536 Long-term intraocular pressure fluctuation and progressive visual field deterioration in patients with glaucoma and low intraocular pressures after a triple procedure, Hong S; Seong GJ; Hong YJ, Archives of Ophthalmology, 2007; 125: 1010-1013

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The role of IOP fluctuation as a predictor for glaucoma progression beyond that of mean IOP reduction remains controversial. Posthoc analysis of data from AGIS has suggested that IOP fluctuation is a major risk factor for visual field progression in glaucoma.¹ However, methodological concerns have been raised. A recent analysis of data from EMGT failed to find a significant role for IOP fluctuation². Hong et al. (1144) explored the association of mean IOP and IOP fluctuation with the functional outcomes in 408 eyes that underwent combined glaucoma and cataract surgery with a mean follow-up of 9.2 &plm; 3.6 years. Eyes with intraocular pressures consistently below 18 mmHg were included. The authors concluded that, despite a seemingly equivalent mean IOP, eyes that had a higher standard deviation of IOP (SD > 2 mmHg) during the follow-up period were more likely to progress compared to eyes that demonstrated a lower SD of IOP (≤ 2 mmHg). The facts that a large number of eyes (408 eyes) were operated by a single surgeon and followed for an average of more than nine years are the main strengths of this manuscript. Also, cataract extraction at the time of glaucoma surgery, removed a potential source of confounding. However, there are several methodological issues that prevent us from fully embracing their conclusions. The authors failed to mention how the cutoff point of 2 mmHg was selected for dividing the study sample. A priori determination of such classification criteria are of major importance in such settings and if not performed properly would potentially bias the results. Also, the authors have not mentioned long-term outcomes of their patients and whether additional laser or incisional surgical procedures were needed. Since the IOP SD data are reported for the whole duration of follow-up, additional surgeries could have led to a higher fluctuation and would be potentially associated with a higher rate of progression since at least some of the second surgical procedures were likely done for progressing eyes. The number of datapoints ('n') for each follow-up point was not provided. Missing data are expected and are quite frequent in retrospective studies.

Further analysis of the data would be needed to better delineate the role of IOP fluctuation with respect to visual field progression

Providing the number of available eyes at each point will help readers judge the validity of the comparisons. Most importantly, multivariate analysis was not performed to adjust for the other known or potentially significant predictive factors for progression. Given the variable follow-up of patients, survival analysis methods with time dependent factors would have been most appropriate. The amount of change in the progressing groups was only about 1 point by AGIS score, which makes it even more important to look at results of multivariate analysis. The authors have addressed an important clinical question in glaucoma management. However, further analysis of the data would be needed to better delineate the role of IOP fluctuation with respect to visual field progression.

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