Background and Aim Rhythmic variations in calibre of retinal veins crossing the optic disc indicate normal CSF pressure. Anecdotal observation of SVP in patients with high opening pressure (OP), led us to determine the sensitivity and specificity of this sign.

Methods We prospectively recruited patients attending for LP. Researchers were blinded to the indication for LP and OP. Inter-observer reliability was assessed.

Results 106 patients (76F) were included. Median (range) age 44 year (18–79), BMI 27.5 kg/m² (18–48). 5 were excluded for failed LP or no recorded OP. SVP present in 94/106 (88.7%). OP 19.8 cmH20 (9–44). 13/106 (12.3%) had high CSF pressure (≥30 cmH20); SVP was absent in 2/13 (15.4%). The sensitivity (95% CI) of absent SVP to predict high OP is 0.15 (0.05 to 0.37), specificity 0.89 (0.88 to 0.92), positive predictive value 0.17 (0.05 to 0.4), negative predictive value 0.88 (0.87 to 0.9). Inter-observer agreement (κ) was moderate for SVP (0.42) and good for papilloedema (0.79). Papilloedema was seen in 36/209 eyes (3 eyes excluded due to poor visualisation of fundi); 13 of those 36 had high OP. Of the 13 patients with papilloedema and high OP, SVP was observed in 6.

Conclusions The high specificity of absent SVP in high OP indicates that the clinical maxim of “presence of SVP excludes raised intracranial pressure” is largely true but not an absolute rule. Relying on the presence of SVP to exclude raised intracranial pressure may give a false sense of reassurance.