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Editors Selection IGR 8-1

Angle closure glaucoma

Comment by Prin Rojanapongpun on:

13366 Narrowing of the anterior chamber angle during Valsalva maneuver: A possible mechanism for angle closure, Dada T; Gupta V; Deepak KK et al., European Journal of Ophthalmology, 2006; 16: 81-91

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Dada et al. (153) raised the question whether the Valsalva maneuver, and perhaps similar physiological changes during daily activities, may be responsible for intermittent angle closure in predisposed eyes. They also reported significant elevations of IOP (mean 10 mmHg) in both angle closure and open angle glaucoma groups. Using UBM before and during the Valsalva maneuver, they demonstrated significant narrowing of the anterior chamber angle recess, thickening of the ciliary body and increase in the iris thickness. However, the magnitude of IOP rise did not correlate with amount of angle recess narrowing. All findings are supported by UBM images and quantitative analysis using well established software (UBM Pro 2000) by a single trained, masked observer. The study size was reasonable good including 76 patients. The study was not prospectively designed to compare findings between the angle closure versus the open angle or normal control. No confidence intervals are reported. Yet, it provides valuable information with certain limitations.

Valsalva maneuver is known to increase intrathoracic pressure following by increased venous pressure. Thus results in increased IOP as well as venous congestion at the uveal tissue. Although the study elegantly demonstrates various changes by UBM, there are several aspects that need to be pointed out. Firstly, it is technically difficult to titrate or standardize intrathoracic pressure raised by Valsalva maneuver. Using a mouth piece manometer may not represent what a real intrathoracic pressure is as physiologic Valsalva shall be a state that glottis is closed. Secondly, the patient in supine position asked to do the Valsalva manouvre for 15 seconds could be different from most daily activities except certain weight training and sexual intercourse posture. Thus, one must be cautious to conclude that all daily activities, Valsalva and alike, will lead to such changes. Thirdly, UBM could be very subjective in both image acquisition and distance measurements. There are certain limitations with the software, also found by the investigators, especially when using in angle closure eyes. The scleral spur, which is not always a well defined point, especially in angle closure eye, has to be manually marked. Though the current UBM measurement provides three-digits figures, its resolution is not really accurate for the second digit. However, there is no doubt that a person with angle closure performing a Valsalva maneuver with enough exertion on pressure and duration, in either prone or supine position, may produce such changes as reported in this study. But we cannot generalize these findings to all other daily Valsalva activities.

Raised IOP during Valsalva maneuver is not new. Dickerman, 1999 showed that IOP could be as high as 46 mmHg during maximal isometric contraction in power athletes. This study reported a peak IOP of 42 mmHg in heterogeneous consecutive series of 76 selected patients, referred for glaucoma consultation. The majority (73.7%) had angle closure glaucoma. The remaining were either POAG or suspects. However, there was no significant difference in IOP rise among the different types of glaucoma. One cannot conclude yet whether the magnitude of IOP changes are not really different between open and closed angle eyes as this study was not designed to provide such answer. The IOP returned to baseline 10-15 seconds after stopping the Valsalva.

It may be logical to speculate that the combination of IOP spike, reduced parasympathetic stimulus resulting in less iris sphincter tone, and uveal venous congestion resulting in change of the peripheral angle, may lead to intermittent angle closure. The study reported no change of anterior chamber depth (ACD). No change of ACD was also found in eyes with acute primary angle closure by Yang, 2005. These findings do not support the hypothesis of forward lens movement and choroidal expansion as the mechanism of angle closure attack. Perhaps, more important are the changes of the far peripheral angle structures.

In conclusion, Dada et al. beautifully demonstrated to us that narrowing of anterior chamber angle and IOP rise can be induced by forced Valsalva maneuver. Such changes could be important in eyes with occludable or closed angle. However, the findings may not be generalized to all daily Valsalva-related activities. Yet it provides us with an important message that we have to communicate to the relevant patients. Other findings of the study also guide us toward further research on possible angle closure attack mechanism. Important changes may be confined at the peripheral

angle structures and not necessarily to the whole choroidal expansion. Perhaps, with the upcoming improved new technology

to image angle structures and uveal tissue, we may have a more efficient way to study changes in each individual and tailor our advices to suit their life styles. Such technology may also allow us to predict who are at high risk of developing angle closure or can develop significant changes of either angle configurations and IOP. Thus allow us a state-of-the-art approach to each individual.

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