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Editors Selection IGR 17-4
Clinical Examination Methods: Factors Affecting IOP
Comment by Yvonne Buys on:
61532 Effect of Different Head Positions in Lateral Decubitus Posture on Intraocular Pressure in Treated Patients with Open Angle Glaucoma, Lee TE; Yoo C; Lin S et al., American Journal of Ophthalmology, 2015; 160: 929-936.e4
The literature regarding the influence of posture on intraocular pressure (IOP) has taught us that as the head assumes a more dependent position IOP increases. This study by Lee et al. confirms this finding in a group of 20 open-angle glaucoma subjects controlled with latanoprost. What is new, however, is exploring the effect of head position while in a common sleep position, lateral decubitus. IOP was measured in a random order with subjects in the right and left lateral decubitus position while varying the position of the head with respect to the thoracic spine; head 30 degrees higher, parallel and 30 degrees lower by stacking pillows.
It is time to think beyond the effects of position on IOP in isolation and start to consider the interaction of IOP, CSFp and BP
As expected, in the lateral decubitus position IOP was higher in the dependent eye and while in the lateral decubitus position IOP was higher when the head was 30 degrees lower. Although the magnitude of this effect varied by subject, in 50% it was ≥ 4 mmHg in the dependent eye with the head lowered compared to sitting reaching a maximum of 8.8 mmHg in one subject. In contrast to other reports, this study failed to find a difference when comparing the better-to-worse eye defining severity by either visual field mean deviation or pattern standard deviation. The authors conclude by suggesting side sleepers consider elevating their head to minimize this IOP increase, however, even with the head 30 degrees elevated, IOP was still higher in the dependent compared to the nondependent eye suggesting that perhaps a better recommendation would be to sleep supine with the head elevated.
The authors acknowledge some of the limitations of their study including small sample size, laboratory setting which may not reflect what occurs during sleep and the short (five minutes) duration of the maintaining the position prior to measuring. Larger questions, however, remain unanswered, namely what is the mechanism of posture-induced IOP changes, what is the effect of neck flexion on venous compression, what is the effect of position on cerebral spinal fluid pressure (CSFp) and blood pressure (BP), and can changing sleep position influence glaucoma progression rates. It is time to think beyond the effects of position on IOP in isolation and start to consider the interaction of IOP, CSFp and BP.
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