Critical flicker frequency (CFF) in man during induced ocular hypertension. II. Technique, and analysis of a normal group

Using critical flicker frequency in the evaluation of visual impairment in preeclamptic women

OBJECTIVE

To assess critical flicker frequency (CFF) in normal uneventful pregnancy and preeclampsia.

STUDY-DESIGN

Case-control observational study at the University Hospital Jena and Outpatient Institute for Prenatal Diagnosis and Preventive Medicine. 25 non-pregnant women, 75 uncomplicated pregnant women in first, second and third trimester, and 15 women with overt preeclampsia. For comparison with preeclamptic patients we matched 15 normal pregnant women (mNP) for age, parity, body mass index, current smoking and family history of cardiovascular disease (CVD). We measured CFF using the portable HEPAtonorm Analyzer (nevoLAB GmbH, Germany). This device generates a flickering red light, starting with a frequency of 60Hz, giving the subjective an impression of a steady light. The participant signifies once the impression of a flickering light is recognized, and this CFF is recorded. Mean CFF and standard deviation is automatically calculated. Statistical analysis was performed using SPSS Version 22 for Windows. Following assessment of normal distribution with Kolmogorov-Smirnow test, comparisons were made with univariate and multivariate ANOVA and with unpaired and paired t test for continuous data and with χ² test for categorical data.

RESULTS

Critical flicker frequency in healthy pregnant women does not differ from nonpregnant women. No significant differences in CFF measurements exist in first, second, and third trimester. In preeclampsia, CFF is significantly decreased compared to normal pregnant women (PE 38.80±2.16 vs. mNP 46.23±3.37; p=0.000). This alteration persists even some weeks postpartum (PE 41.17±1.13 vs. mNP 46.45±3.44; p=0.003).

CONCLUSION

In preeclamptic women, CFF is decreased indicating an altered endothelial situation. The finding that CFF remains reduced postpartum may be explained by either the effect of preeclampsia on maternal endothelium causing longer lasting damage or indicate a preexisting endothelial disorder. Up to this point, precise responsible mechanisms for altered CFF in preeclampsia are currently unclear and further studies are needed.

Differential effects of compression and suction ophthalmodynamometry on the scotopic blue-flash electroretinogram

Several studies have investigated the effect of elevated intraocular pressure with reduced ocular perfusion pressure on visual neural function by means of compression and suction ophthalmodynamometry. We compared the effects of nominally equivalent reductions in the ocular perfusion pressure induced by compression and suction ophthalmodynamometry retinal function as measured by flash electroretinography. Scotopic blue-flash electroretinograms were recorded in five subjects for baseline conditions; during a 40% reduction in the ocular perfusion pressure effected in a first test session by compression ophthalmodynamometry; and then in a second test session some 4 hours later by suction ophthalmodynamometry. Fifteen consecutive electroretinographic sets were recorded during scleral compression or suction, and also after compression or suction was removed. Compression and suction ophthalmodynamometry decreased the electroretinogram b-wave to different degrees; overall, the electroretinogram was attenuated more by compression than by suction ophthalmodynamometry. In the recovery phase, the group averaged b-wave quickly increased to exceed baseline after both scleral compression and suction. The trends for prolonged implicit times over the duration of the study were similar for compression and suction ophthalmodynamometry.