Flicker defined form and RareBit measurements lack in specificity of visual pathways.

AIM

To evaluate the different visual pathways represented by the Heidelberg Engineering Perimeter flicker defined form and RareBit (magnocellular and parvocellular respectively) in different age-groups and according to the fatigue.

METHODS

Totally 64 eyes of 32 healthy subjects were included in the prospective study. Each participant underwent screening-ophthalmic examination including best-corrected visual acuity, anterior and posterior segment assessment, and visual field examination with Heidelberg Edge Perimetry (HEP)-standard automated perimeter (SAP) 24-2. They were observed for 2y previously to the enrollment. This helped to define that the enrolled patients did not bear the glaucoma-developing potential. During the screening and after two years the HEP had been conducted in the standard protocol 24-2 and RareBit perimetry (RBP) in accordance with the manufacturer's description. Participants were randomly assigned to the groups: flicker defined form (FDF)-first or RBP-first. This defined from which additional visual field test the participant started. Participants were additionally subdivided to younger and older study groups. The effect of subject variables was explored with Mann-Whitney -test. Testing for the presence of correlations between parameters was performed using the Spearman Rank Order Correlations and confirmed by the parametric tests. For the influence of additional factors, the Kruskal-Wallis test was performed.

RESULTS

The positive correlation between mean deviation (MD) and mean hit rate (MHR) and pattern standard deviation (PSD) and standard deviation of MHR (±MHR) were found in younger study group (=0.005, =0.481 and =0.0074, =0.465), whereas in the older subgroup no correlation was observed. Additionally, the randomization protocol helped in defining the role of fatigue on the HEP-FDF results. Participant for whom the HEP-FDF was performed after RareBit had significantly worse results than those for whom the HEP-FDF was first. In the younger group, the MHR and ±MHR depend from age in that group (<0.05, =0.43 and =-0.57 respectively) while no age-dependent differences were found in HEP-related parameters. On the contrary in the older group the MD and PSD varies with age (<0.05, =0.47 and = -0.44 respectively) while the RBP parameters remained unchanged. The questionnaire showed that participants preferred RareBit over HEP-FDF in terms of a duration time, comfort, understanding of the test procedures, and ocular pain (<0.05).

CONCLUSION

The influence of patient's fatigue should be considered during HEP-FDF examination. An overlap hypothesis should be reevaluated after determining of other factors that affect HEP-FDF and RareBit results.