ABSTRACT
AIM: To investigate the effects of baffle and intraocular pressure (IOP) on the aerosols generated in the noncontact tonometer (NCT) measurement and provide recommendations for the standardized use of the NCT during coronavirus disease 2019 (COVID-19). METHODS: This clinical trial included 252 subjects (312 eyes) in The Eye Hospital, Wenzhou Medical University from March 7, 2020, to March 28, 2020. Sixty subjects (120 eyes) with normal IOP were divided into two groups. One group used an NCT without a baffle, another group used an NCT with a baffle. Another 192 subjects (192 eyes) were divided into four groups: Group A1 (without a baffle+normal IOP), Group A2 (without a baffle+high IOP), Group B1 (with a baffle+normal IOP) and Group B2 (with a baffle+high IOP). Particulate matter (PM) 2.5 and PM10 generated by all subjects were quantified during the NCT measurement. The IOP values were recorded simultaneously. Effects of baffle and IOP on aerosols generated during the NCT measurement were analyzed. RESULTS: In the normal eye group with a baffle, the aerosol density decreased in a wave-like shape near the NCT with the increase in the number of people measured for IOP, demonstrating no cumulative effect. However, in the normal eye group without a baffle, there was a cumulative effect. PM2.5 and PM10 in Group A2 were higher than Group A1 (both P<0.001). The PM2.5 and PM10 in Group B2 were higher than Group B1 (P<0.01, P<0.001 respectively). The PM10 of Group B1 was lower than Group A1 (P<0.01). PM2.5 in Group B2 were lower than Group A2 (P<0.01). The median of per capita PM2.5 and PM10 in the combined Group A1+A2 were 0.80 and 1.10 µg/m3 respectively, which were higher than 0.20 and 0.60 µg/m3 in the combined Group B1+B2 (both P<0.01). The median of per capita PM2.5 and PM10 in the combined Group A1+B1 were 0.10 and 0.20 µg/m3 respectively, which were lower than 1.30 and 1.70 µg/m3 in the combined Group A2+B2 (both P<0.001). CONCLUSION: More aerosols could be generated in patients with high IOP. After the NCT is equipped with a baffle, per capita aerosol density generated decreased significantly near the NCT; And with the increase in the number of people measured for IOP, the aerosols gradually dissipated near the NCT, demonstrating no cumulative effect. Therefore, it is suggested that the NCT should be equipped with a baffle, especially for patients with high IOP.
ABSTRACT
All known riboswitches use their aptamer to senese one metabolite signal and their expression platform to regulate gene expression. Here, we characterize a SAM-I riboswitch (SAM-IXcc) from the Xanthomonas campestris that regulates methionine synthesis via the met operon. In vitro and in vivo experiments show that SAM-IXcc controls the met operon primarily at the translational level in response to cellular S-adenosylmethionine (SAM) levels. Biochemical and genetic data demonstrate that SAM-IXcc expression platform not only can repress gene expression in response to SAM binding to SAM-IXcc aptamer but also can sense and bind uncharged initiator Met tRNA, resulting in the sequestering of the anti-Shine-Dalgarno (SD) sequence and freeing the SD for translation initiation. These findings identify a SAM-I riboswitch with a dual functioning expression platform that regulates methionine synthesis through a previously unrecognized mechanism and discover a natural tRNA-sensing RNA element. This SAM-I riboswitch appears to be highly conserved in Xanthomonas species.