Accuracy of noninvasive intraocular pressure or optic nerve sheath diameter measurements for predicting elevated intracranial pressure in cryptococcal meningitis

Abstract

Background. Cryptococcal meningitis is associated with increased intracranial pressure (ICP). Therapeutic lumbar puncture (LP) is recommended when the initial ICP is > 250 mm H2O, yet the availability of manometers in Africa is limited and not always used where available. We assessed whether intraocular pressure could be a noninvasive surrogate predictor to determine when additional therapeutic LPs are necessary. Methods. Ninety-eight human immunodeficiency virus-infected Ugandans with suspected meningitis (81% Cryptococcus) had intraocular pressure measured using a handheld tonometer (n = 78) or optic nerve sheath diameter (ONSD) measured by ultrasound (n = 81). We determined the diagnostic performance of these methods for predicting ICP vs a standard manometer. Results. The median ICP was 225 mm H2O (interquartile range [IQR], 135-405 mm H2O). The median intraocular pressure was 28 mm Hg (IQR, 22-37 mm Hg), and median ultrasound ONSD was 5.4 mm (IQR, 4.95-6.1 mm). ICP moderately correlated with intraocular pressure (ρ = 0.45, P < .001) and with ultrasound ONSD (ρ = 0.44, P < .001). There were not discrete threshold cutoff values for either tonometry or ultrasound ONSD that provided a suitable cutoff diagnostic value to predict elevated ICP (> 200 mm H2O). However, risk of elevated ICP >200 mm H2O was increased with an average intraocular pressure > 28 mm Hg (relative risk [RR] = 3.03; 95% confidence interval [CI], 1.55-5.92; P < .001) or an average of ONSD > 5 mm (RR = 2.39; 95% CI, 1.42-4.03; P = .003). As either intraocular pressure or ONSD increased, probability of elevated ICP increased (ie, positive predictive value increased). Conclusions. Noninvasive intraocular pressure measurements by tonometry or ultrasound correlate with cerebrospinal fluid opening pressure, but both are a suboptimal replacement for actual ICP measurement with a manometer.