Purpose
To investigate the effect of change of body posture from the supine to the lateral decubitus position on intraocular pressure (IOP) in patients with open-angle glaucoma.
Design
Prospective, observational case series.
Methods
Setting. Institutional. Participants. Forty-four eyes of 22 patients with newly diagnosed bilateral open-angle glaucoma. Observation procedures. IOP was measured using the Tono-Pen XL (Reichert Inc) in both eyes 10 minutes after assuming each position: sitting, supine, right lateral decubitus, supine, left lateral decubitus, and supine. By comparing the mean deviation (MD) of Humphrey visual field between both eyes of a patient, eyes were classified into either worse-MD eye or better-MD eye. Main outcome measures. Magnitude of IOP alterations by postural changes and intereye difference of IOP with each posture.
Results
The mean ± SD IOP of the dependent eyes (eye on the lower side in the lateral decubitus position) increased after changing from the supine to the right lateral decubitus position (19.1 ± 2.6 mm Hg vs 21.0 ± 2.7 mm Hg; P = .019) or the left lateral decubitus position (18.6 ± 2.9 mm Hg vs 20.6 ± 3.1 mm Hg; P = .002). The mean IOP of the dependent eyes was significantly higher than that of the nondependent eyes in the lateral decubitus positions (right lateral decubitus, +1.2 mm Hg; left lateral decubitus, +1.6 mm Hg; both, P < .05). Compared with the better-MD eyes, the worse-MD eyes showed a tendency for greater IOP rise with positional change from the supine to lateral decubitus position (2.3 ± 2.2 mm Hg vs 1.5 ± 2.1 mm Hg; P = .065).
Conclusions
The postural change from the supine to lateral decubitus position may increase the IOP of the dependent eyes in patients with open-angle glaucoma.
Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of glaucoma. Alterations of body posture have been shown to influence IOP. A number of studies have demonstrated that IOP measured in the supine position is higher than that in the sitting position in normal subjects and that such a postural change in IOP may be greater in patients with glaucoma. This IOP increase in the supine position may be an important contributor for the IOP elevation observed at night and has been shown to be associated with progression of open-angle glaucoma (OAG).
During sleep, one’s body may rest not only in the supine or prone positions, but also in the lateral position. A side sleeping position has been shown to be preferred as age advances. Thus, the effect of the lateral decubitus position on IOP may be important clinically to the management of glaucoma.
With regard to the relationship between the lateral decubitus position and IOP, Hwang and associates prospectively evaluated the effect of the lateral decubitus position on IOP in patients undergoing lung surgery and found that IOP in the lateral decubitus position consistently was higher in the dependent eye (the eye on the lower side) than that in the nondependent eye throughout the surgery. Previously, we found that the postural change from the supine to lateral decubitus position significantly increased the IOP of the dependent eye in healthy young subjects. A recent study by Malihi and Sit also demonstrated an increase in IOP in the dependent eye in both lateral decubitus positions after 5 minutes in healthy young subjects. However, to date, we are aware of no study in the literature that has explored the effect of the lateral decubitus position on IOP in patients with glaucoma.
We conducted this study to investigate IOP alterations of body posture from the supine to the lateral decubitus position in patients with OAG and the relationship between the IOP change in such a postural shift and the visual field damage.
Methods
This prospective, observational case series was conducted at the Department of Ophthalmology, Korea University College of Medicine. Thirty-nine patients were newly diagnosed with bilateral primary OAG at the Korea University Anam Hospital between October 2010 and February 2011. Among these, 22 consecutive patients with newly diagnosed, untreated bilateral OAG provided informed consent to participate in the study.
Each patient underwent comprehensive ophthalmic examinations of both eyes, including best-corrected visual acuity, refractive error, slit-lamp biomicroscopy, central cornea thickness with noncontact specular microscope (sp-3000p; Topcon, Tokyo, Japan), gonioscopy, Goldmann applanation tonometry, Humphrey Swedish interactive threshold algorithm 30-2 testing (Zeiss-Humphrey, San Leandro, California, USA), and dilated 30-degree stereoscopic photography and 50-degree red-free photography using a Zeiss FF450 IR plus camera (Carl Zeiss Meditec Inc, Dublin, California, USA).
OAG was diagnosed when glaucoma hemifield test results were outside the normal limits or the standard deviation had a P value of less than .05, or when there was a cluster of 3 points or more in the pattern of the deviation plot in a single hemifield with a P value of less than .05, 1 of which had to have a P value of less than .01 on the Humphrey Swedish interactive threshold algorithm 30-2 test, a nerve fiber layer defect combined with a corresponding optic disc change, or both. Untreated IOPs were measured by Goldmann applanation tonometer on the first visit during 1 of the following 3 periods: from 8 am and 11 am , from 11 am to 2 pm , or from 2 pm to 5 pm . Two additional IOP measurements were obtained at different periods on the next visits within 2 weeks. The median of 3 consecutive measurements was recorded each time. All the evaluations other than IOP measurements were carried out at the first visit. Gonioscopy excluded angle closure, rubeosis, and secondary glaucoma. Patients with concomitant ocular disease, best-corrected visual acuity worse than 20/40, refractive error of more than 9 diopters spherical equivalent or 2 diopters of astigmatism, use of contact lenses, systemic use of steroid or β-blockers, or a history of previous intraocular surgery were excluded from this study.
After the baseline examination was completed for diagnosis of OAG, each participant was asked to revisit our laboratory 1 week later for serial IOP measurements in different body postures. Subjects were instructed to abstain from alcohol for 3 days and caffeine for 1 day. IOP measurements were obtained between 9:00 am and 11:00 am . A single observer, masked to patients’ characteristics, measured IOP using a single Tono-Pen XL (Reichert Inc, Depew, New York, USA) in both eyes for every time point. Proparacaine 0.5% was used as local anesthetic. The right eye always was examined first. To avoid a bias, the Tono-Pen was calibrated according to the manufacturer’s instructions before measurements at each time point. Measurements were made with the probe perpendicular to the corneal plane and along the visual axis. IOP value at each time point was the mean of 2 consecutive measurements that were within 2 mm Hg and that had less than 5% error as indicated on the Tono-Pen or the median of 3 measurements if the first 2 differed by 3 mm Hg or more.
Each participant was asked to sit on a backrest chair in a quiet room under dim light conditions. Ten minutes later, IOP was measured in the sitting position (T1). Then, the subject was asked to lie on a flat bed with a soft pillow underneath the head and to maintain the supine position comfortably, and IOP was measured 10 minutes later (T2). Subsequently, the subject was asked to turn right to assume the right lateral decubitus position. The subject rested his or her head on a soft pillow so that the head was kept parallel to the bed. IOP was measured at 10 minutes (T3) after this positional change to the right lateral decubitus and was measured again at 10 minutes (T4) after returning to the supine position. Then, the subject was asked to assume the left lateral decubitus position, and IOP was measured 10 minutes later (T5). Finally, IOP was measured at 10 minutes (T6) after returning to the supine position. The subject was instructed to keep awake during the period of these positional changes and to look straight ahead during IOP measurements. The eye on the lower side in the lateral decubitus position was considered the dependent eye.
Statistical Analysis
A pilot study of 10 patients revealed that the standard deviation of IOP difference of the dependent eyes during postural change from the supine to the right lateral decubitus position was 2.6 mm Hg (3.2 mm Hg for that during the postural shift to the left lateral decubitus position). A sample size calculation determined that 22 patients would be required to detect an IOP difference of more than 2 mm Hg in the dependent eyes at a standard deviation of 3.2 mm Hg with a power of 80%. All statistical analyses were performed using SPSS software version 12.0 (SPSS Inc, Chicago, Illinois, USA). The repeated measures analysis of variance with Bonferroni correction was used to compare IOP alterations by changing body posture. The repeated measures analysis of variance also was used to assess the intereye IOP differences in each time point and to compare the magnitude of IOP alterations during positional changes between the eyes with worse mean deviation (MD) and those with better MD based on the Humphrey visual field tests. A P value of less than .05 was considered statistically significant unless the Bonferroni correction method for multiple comparisons was used, in which case a P value of less than .003 was considered statistically significant.
Results
This study was conducted in compliance with the tenets of the Declaration of Helsinki for the use of human subjects in biomedical research and in compliance with regional laws regarding maintenance of the privacy of patient data. The institutional review board approval was prospective, and informed consent statements for research from each participant were obtained.
There were 9 women and 13 men with a mean age of 49.5 ± 11.2 years. Refractive errors, central cornea thickness, visual field indices did not differ between the right and left eyes of the subjects ( Table 1 ).
| Right Eye (n = 22) | Left Eye (n = 22) | P Value a | |
|---|---|---|---|
| SE (D) | −2.49 ± 3.13 | −2.15 ± 2.88 | .078 |
| IOP (mm Hg) b | 16.4 ± 2.6 | 16.3 ± 2.5 | .366 |
| CCT (μm) | 513.7 ± 26.6 | 517.7 ± 29.0 | .108 |
| MD (dB) | −6.75 ± 5.28 | −5.44 ± 4.70 | .709 |
| PSD (dB) | 7.70 ± 4.82 | 5.70 ± 4.05 | .115 |
Table 2 shows the mean IOPs at each time point during changing body postures among the sitting, supine, and lateral decubitus positions. No significant intereye IOP difference was found in the sitting position (T1) or supine positions (T2, T6). The IOP of the dependent eyes was significantly higher than that of the nondependent eyes at 10 minutes after changing from the supine to the right lateral decubitus position (T3, +1.2 mm Hg; P = .023) and also at 10 minutes after changing from the supine to the left lateral decubitus position (T5, +1.6 mm Hg; P = .004). In addition, the IOP of right eyes was significantly higher than that of the left eyes at 10 minutes after returning from the right lateral decubitus to the supine position (T4, +1.1 mm Hg; P = .002).
| Time Point | IOP (Mean ± SD) | Mean Difference | Standard Error | P Value a | |
|---|---|---|---|---|---|
| Right Eye | Left Eye | ||||
| T1 | 17.3 ± 2.8 | 17.1 ± 2.6 | 0.3 | 0.3 | .386 |
| T2 | 19.1 ± 2.6 | 19.6 ± 2.9 | −0.5 | 0.3 | .067 |
| T3 | 21.0 ± 2.7 | 19.8 ± 3.1 | 1.2 | 0.5 | .023 |
| T4 | 19.7 ± 2.7 | 18.6 ± 2.9 | 1.1 | 0.3 | .002 |
| T5 | 19.1 ± 3.2 | 20.6 ± 3.1 | −1.6 | 0.5 | .004 |
| T6 | 18.8 ± 3.3 | 18.9 ± 3.3 | −0.1 | 0.3 | .682 |
Table 3 lists the statistical differences of IOP alterations in each eye between time points during changing body postures. IOPs in both eyes were higher in the supine position (T2) than in the sitting position (T1). Compared with the supine position (T2), the IOP of right eyes showed a rise in the right lateral decubitus position (T3), although the difference was of borderline significance. A significant IOP alteration was not found in the nondependent (left) eyes during postural changes between T2 and T4. After assuming the left lateral decubitus position (T5), a significant rise of IOP in the dependent (left) eyes was detected compared with that measured 10 minutes after changing from right lateral decubitus to the supine position (T4). In the nondependent (right) eyes, no significant IOP alteration was found during postural changes between T4 and T6 ( Figure ).
| Between 2 Time Points | ΔIOP | Right Eye | Left Eye | P Value a | ||
|---|---|---|---|---|---|---|
| 95% CI | P Value | ΔIOP | 95% CI | |||
| T1 to T2 | 1.8 ± 0.3 | 0.7 to 2.9 | < .001 | 2.6 ± 0.4 | 1.3 to 3.8 | < .001 |
| T1 to T3 | 3.7 ± 0.5 | 1.9 to 5.4 | < .001 | 2.7 ± 0.5 | 1.2 to 4.2 | < .001 |
| T1 to T4 | 2.4 ± 0.4 | 1.1 to 3.7 | < .001 | 1.6 ± 0.5 | 0.1 to 3.1 | .038 |
| T1 to T5 | 1.7 ± 0.6 | −0.4 to 4.0 | .178 | 3.5 ± 0.6 | 1.5 to 5.6 | < .001 |
| T1 to T6 | 1.5 ± 0.5 | 0.0 to 3.0 | .051 | 1.9 ± 0.5 | 0.3 to 3.5 | .013 |
| T2 to T3 | 1.9 ± 0.5 | 0.2 to 3.5 | .019 | 0.2 ± 0.4 | −1.2,1.5 | 1.000 |
| T2 to T4 | 0.6 ± 0.3 | −0.5 to 1.6 | 1.000 | −1.0 ± 0.4 | −2.3 to 0.3 | .277 |
| T2 to T5 | −0.1 ± 0.6 | −1.9 to 1.7 | 1.000 | 1.0 ± 0.5 | −0.8 to 2.7 | 1.000 |
| T2 to T6 | −0.3 ± 0.4 | −1.6 to 1.0 | 1.000 | −0.7 ± 0.4 | −2.1 to 0.7 | 1.000 |
| T3 to T4 | −1.3 ± 0.4 | −2.7 to 0.1 | .101 | −1.2 ± 2.1 | −2.6 to 0.3 | .244 |
| T3 to T5 | −2.0 ± 0.5 | −3.6 to −0.3 | .014 | 0.8 ± 0.6 | −1.1 to 2.7 | 1.000 |
| T3 to T6 | −2.2 ± 0.6 | −4.0 to −0.4 | .011 | −0.9 ± 0.5 | −2.4 to 0.7 | 1.000 |
| T4 to T5 | −0.7 ± 2.3 | −2.3 to 1.0 | .200 | 2.0 ± 0.4 | 0.6 to 3.3 | .002 |
| T4 to T6 | −0.9 ± 0.4 | −2.2 to 0.4 | .466 | 0.3 ± 0.4 | −0.9 to 1.5 | 1.000 |
| T5 to T6 | −0.2 ± 0.5 | −1.8 to 1.3 | 1.000 | −1.7 ± 0.5 | −3.3 to 0.0 | .052 |
a Repeated measures analysis of variance with adjustment for multiple comparisons by Bonferroni correction.
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