A common method for measuring changes in temporal processing sensitivity in both humans and animals makes use of GaP-induced Inhibition of the Acoustic Startle (GPIAS). It is also the basis of a common method for detecting tinnitus in rodents. However, the link to tinnitus has not been properly established because GPIAS has not yet been used to objectively demonstrate tinnitus in humans. In guinea pigs, the Preyer (ear flick) myogenic reflex is an established method for measuring the acoustic startle for the GPIAS test, while in humans, it is the eye-blink reflex. Yet, humans have a vestigial remnant of the Preyer reflex, which can be detected by measuring skin surface potentials associated with the Post-Auricular Muscle Response (PAMR). A similar electrical potential can be measured in guinea pigs and we aimed to show that the PAMR could be used to demonstrate GPIAS in both species. In guinea pigs, we compare the GPIAS measured using the pinna movement of the Preyer reflex and the electrical potential of the PAMR to demonstrate that the two are at least equivalent. In humans, we establish for the first time that the PAMR provides a reliable way of measuring GPIAS that is a pure acoustic alternative to the multimodal eye-blink reflex. Further exploratory tests showed that while eye gaze position influenced the size of the PAMR response, it did not change the degree of GPIAS. Our findings confirm that the PAMR is a sensitive method for measuring GPIAS and suggest that it may allow direct comparison of temporal processing between humans and animals and may provide a basis for an objective test of tinnitus.
PURPOSE/AIM: Wink glass (WG), an invention to stimulate blinking at interval of 5 s was designed to reduce dry eye symptoms during visual display unit (VDU) use. The objective of this study is to investigate the effect of WG on visual functions that include blink rate, ocular surface symptoms (OSS) and tear stability during VDU use.
MATERIALS AND METHODS: A total of 26 young and asymptomatic subjects were instructed to read articles in Malay language with a computer for 20 min with WG whereby their blink rate, pre- and post-task tear break-up time, and OSS were recorded. The results were compared to another reading session of the subjects wearing a transparent plastic sheet as a control.
RESULTS: Non-invasive tear break-up time was reduced after reading session with transparent plastic sheet (pre-task = 5.97 s, post-task = 5.14 s, z = -2.426, p = 0.015, Wilcoxon), but remained stable (pre-task = 5.62 s, post-task = 5.35 s, z = -0.67, p = 0.501) during the reading session with WG. The blink rate recorded during reading session with plastic sheet was 9 blinks/min (median) and this increased to 15 blinks/min (z = -3.315, p = 0.001) with WG. The reading task caused OSS (maximum scores = 20) with median score of 1 (0-8) reduced to median score of 0 (0-3) after wearing WG (z = -2.417, p = 0.016).
CONCLUSION: WG was found to increase post-task tear stability, increased blinking rate and reduced OSS during video display unit use among young and healthy adults. Although it may be considered as an option to improve dry eye symptoms among VDU users, further studies are warranted to establish its stability and its effect on subjects with dry eyes.
KEYWORDS: Blink rate; Wink glass; non-invasive tear break-up time; visual display units