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

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.