Bilateral recording of human intraocular pressure with an improved applanating suction cup tonograph

An improved applanating suction cup for continuous recording of human intraocular pressure is described. The new cup adheres better, is easier to calibrate, and is simpler to handle, mainly due to a different curvature of the applanating surface. The interspace between the applanating and the applanated surface, in which the pressure is measured, is continuously flushed with saline from a flow system (Intraflo) connected to the dome of the pressure transducer. The suction that attaches the cup to the cornea is - as in the previous model - provided by a saline filled tube hanging from the cup. In 51 human cadaver eyes the calibration for static pressures and pressures oscillating up to 124 cycles per min was: intraocular pressure = 0.9 X cup pressure -3 (mmHg), r = 0.995. The cup reduced ocular rigidity by 5% only and increased the intraocular pressure transiently by 4 mmHg when applied. Simultaneous bilateral recordings were obtained in 400 normo- or hypertensive eyes from 206 subjects. The cup was atraumatic, and the method can be strongly recommended when accurate, bilateral pressure recordings are desired for periods up to one h in supine subjects. At intraocular pressures above 35 mmHg, the tonograph may underestimate the pressure under certain, unfavourable conditions.