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Editors Selection IGR 9-4
IOP and Trabecular Meshwork: Asymmetry of IOP fluctuations
Comment by Arthur Sit on:
45511 Asymmetry of diurnal intraocular pressure fluctuation between right and left eyes, Kim MS; Kim JM; Park KH et al., Acta Ophthalmologica, 2011; 89: 352-357
The monocular trial has been a widely used technique for evaluating individual response to topical glaucoma medications. However, the accuracy of the monocular trial in predicting fellow eye response was brought into question by Realini et al.1,2 Research showing asymmetry of IOP between right and left eyes created further doubt about the utility of this test.3,4 However, the factors that are associated with asymmetric fluctuations have not previously been reported. Kim et al. (637) evaluated the asymmetry of IOP fluctuations and associated factors in a group of 102 non-glaucomatous patients using diurnal pressure measurements. They found that IOP measured every two hours during the diurnal period between 0900h to 2300h showed a high degree of correlation between the two eyes. However, when examining IOP fluctuations over two-, four-, and six-hour intervals, there was a high incidence of asymmetric fluctuations ≥ 2 mmHg (10.9 ± 1.6%). Using multivariate analysis, age, anterior chamber depth, lens thickness, and axial length were found to be statistically significant factors associated with the frequency of asymmetric IOP fluctuations. Most systemic factors, including sex, the presence of systemic hypertension or diabetes, body mass index, and blood pressure were not significant factors.
IOP in right and left eyes are highly correlated, but variable enough to make interpretation of a monocular trial difficult
This study is consistent with previous research that demonstrates a high degree of correlation between IOP of right and left eyes, but there is enough variability to make interpretation of a monocular trial difficult. The factors that were associated with the frequency of asymmetric IOP fluctuations were primarily local factors that may be related to outflow facility. Since eyes with decreased outflow facility are susceptible to larger IOP fluctuations,5 asymmetric fluctuations may be related to differences in outflow facility between the two eyes. One issue with this study is that it examined non-glaucoma patients. Since glaucoma patients typically having impaired outflow facility, the frequency of asymmetric fluctuations may be greater than in non-glaucoma patients. Importantly, this study did not assess the nocturnal period and it is therefore unclear if the same risk factors are associated with the magnitude of the nocturnal IOP elevation seen in most individuals. As well, further work is required to confirm whether or not aqueous humor dynamic factors, such as outflow facility, are indeed related to the asymmetry and magnitude of IOP fluctuations.
References
- Realini T, Barber L, Burton D. Frequency of asymmetric intraocular pressure fluctuations among patients with and without glaucoma. Ophthalmology 2002; 109: 1367-1371.
- Realini TD. A Prospective, randomized, investigator-masked evaluation of the monocular trial in ocular hypertension or open-angle glaucoma. Ophthalmology 2009; 116: 1237-1242.
- Liu JH, Sit AJ, Weinreb RN. Variation of 24-hour intraocular pressure in healthy individuals: right eye versus left eye. Ophthalmology 2005; 112: 1670-1675.
- Sit AJ, Liu JH, Weinreb RN. Asymmetry of right versus left intraocular pressures over 24 hours in glaucoma patients. Ophthalmology 2006; 113: 425-430.
- Brubaker RF. Targeting outflow facility in glaucoma management. Surv Ophthalmol 2003; 48 Suppl 1: S17-20.
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