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Sungwon Rachel Kyung, Palak Wall, Brandy Hayden, Paul Rychwalski; The Accuracy of the 30 Degree Test in Detecting Increased Intracranial Pressure When Compared to CSF Opening Pressure on Lumbar Puncture. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2314.
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Ophthalmic ultrasonography (US) is a non-invasive and relatively economical study that can provide valuable information about intraocular and retrobulbar structures. The 30-degree US test is performed by examining the retrobulbar optic nerve sheath width of a patient in a 30-degree eccentric gaze in comparison to the width in primary gaze. It has been theorized that increased intracranial pressure (ICP) would result in significant reduction of the optic nerve sheath width when stretched. However, little is known regarding the accuracy of this test in determining increased ICP. The purpose of our study is to evaluate the accuracy of the 30-degree US test as a measure of detecting increased ICP.
52 charts were retrospectively analyzed via chart review and 19 patients met inclusion criteria. Inclusion criteria required patients to have undergone the 30-degree test (both A-scan and B-scan) along with a lumbar puncture with opening pressure measured for comparison; two patients underwent the US test twice, with a lumbar puncture following each test. Normal ranges for optic nerve US findings were set at an optic nerve sheath width of 2.2 - 3.3 mm, a positive 30-degree test was defined as a >15% reduction in nerve sheath width following a 30-degree eccentric gaze, and a 10-15% reduction was noted as a borderline positive result. Increased ICP parameters were set as an opening pressure of ≥ 240 mmHg for both pediatric and adult populations. Sensitivity, specificity, and predictive values were calculated.
A total of 21 US scan results were compared to lumbar puncture opening pressure values in patients with suspected increased ICP. The 30-degree test was found to be highly sensitive (100%) but non-specific (36.4%). Although there was a high negative predictive value (100%), the positive predictive value was significantly lower (58.8%). The chi-square value was found to be 4.492, and our calculated p-value of 0.034 confirmed these results to have significant correlation.
The 30-degree US test to measure optic nerve sheath width may be a sensitive and effective technique in screening for increased ICP in patients who may not be able to tolerate more invasive methods such as an MRI or lumbar puncture. However, the test is highly non-specific, and further studies would be required to diagnostically identify increased ICP.
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