[Modification of refraction and visual noise perception by suction cup oculocompression]

In 17 ocularly healthy persons the IOP was artificially raised by suction cup oculopression (negative pressure: 65 mmHg [8.67 kPa]) from initially 15.5 +/- 2.2 mmHg (2.07 +/- 0.29 kPa) to 25.2 +/- 4.0 mm Hg (3.36 +/- 0.53 kPa) (mean +/- SD). Continuing the initial refractive correction, visual acuity (Landolt's rings) decreased from initially 1.06 +/- 0.13 to 0.39 +/- 0.22 (P less than 0.001* [*t-test, paired ties each]). A new optical refraction with suction cup in position significantly raised the visual acuity to 0.64 +/- 0.24 (P less than 0.002*). The suction cup itself induced astigmatism of 2.15 +/- 1.46 dpt (Canon Auto-Refractometer RK-1), which significantly differed from the initial astigmatism (0.32 +/- 0.23 dpt) (P less than 0.001*). The minus cylinder axis initially showed no preferential position. During artificial IOP elevation it shifted to 90 degrees...125 degrees (referred to the right eye) and thus ran about perpendicular to the meridian the suction cup was positioned on the eyeball. Effects of such refractive changes on differential light threshold and VEP amplitude are demonstrated. The results presented allow critical interpretation of previous IOP tolerance tests. The influence of suction cup oculopression on the perception of the white-noise field is shown in some glaucoma patients: the speed of the white-noise campimetry allows the increase in field defects during artificial IOP elevation to be followed up directly.