Microstructural evaluation and recommendations for face masks in community use to reduce the transmission of respiratory infectious diseases.

BACKGROUND AND OBJECTIVE: Recommendations for the use of face masks to prevent and protect against the aerosols (≤5µm) and respiratory droplet particles (≥5µm), which can carry and transmit respiratory infections including severe acute respiratory syndrome coronavirus (SARS-CoV-2), have been in effect since the early stages of the coronavirus disease 2019 (COVID-19). The particle filtration efficiency (PFE) and air permeability are the most crucial factors affecting the level of pathogen transmission and breathability, i.e. wearer comfort, which should be investigated in detail. METHODS: In this context, this article presents a novel assessment framework for face masks combining X-ray microtomography and computational fluid dynamics simulations. In consideration to their widespread public use, two types of face masks were assessed: (I) two layer non-woven face masks and (II) the surgical masks (made out of a melt-blown fabric layer covered with two non-woven fabric layers). RESULTS: The results demonstrate that the surgical masks provide PFEs over 75% for particles with diameter over 0.1µm while two layer face masks are found out to have insufficient PFEs, even for the particles with diameter over 2µm (corresponding PFE is computed as 47.2%). Thus, existence of both the non-woven fabric layers for mechanical filtration and insertion of melt-blown fabric layer(s) for electrostatic filtration in the face masks were found to be highly critical to prevent the airborne pathogen transmission. CONCLUSIONS: The present framework would assist in computational assessment of commonly used face mask types based on their microstructural characteristics including fiber diameter, orientation distributions and fiber network density. Therefore, it would be also possible to provide new yet feasible design routes for face masks to ensure reliable personal protection and optimal breathability.

The Effect of Ascorbic Acid (Vitamin C) on Transepithelial Corneal Cross-Linking in Rabbits.

PURPOSE: To evaluate the effects of ascorbic acid (vitamin C), the main antioxidant agent in the cornea on transepithelial corneal cross-linking (CXL) where the main mechanism is oxidation. METHODS: Twenty eyes of 20 rabbits were divided into 3 groups: Group 1 (7 eyes) had transepithelial corneal CXL after being fed with normal diet; Group 2 (7 eyes) had corneal CXL after once-daily subcutaneous injections of 200 mg of ascorbic acid in addition to normal diet; and the control group (6 eyes) was fed with normal diet but did not have corneal CXL performed. Ascorbic acid levels were measured in aqueous humor and plasma, and biomechanical measurements were applied to the cornea. RESULTS: There was a significant difference in ascorbic acid levels of plasma (P = 0.008) and aqueous humor (P = 0.006) between group 1 and 2. The Young's modulus values of group 1 and 2 were similar (P = 0.741) and were significantly higher than the control group (P = 0.02 and P = 0.01). The increase rate in Young's modulus values was 37.3% in group 1 and 43.9% in group 2 compared to control group. The ultimate strain values in group 1 and 2 were similar (P = 0.632) and were significantly higher than control group (P = 0.04, P = 0.03). The ultimate stress values in group 1 and 2 were similar (P = 0.836) and were significantly lower than control group (P = 0.001, P = 0.001). CONCLUSIONS: Systemic vitamin C does not appear to decrease effectiveness of transepithelial corneal CXL. Therefore, there is no reason to stop or reduce vitamin C supplementation before corneal CXL therapy.

Assessment of Corneal Densitometry in Rheumatoid Arthritis Patients.

OBJECTIVES: To evaluate corneal densitometry and anterior segment parameters of rheumatoid arthritis (RA) patients and compare these results with those of age-matched healthy control subjects. MATERIALS AND METHODS: Anterior segment parameters and corneal densitometry of patients with RA and healthy control subjects were assessed by Scheimpflug corneal topography. For densitometry analysis, the 12-mm diameter area of the cornea was subdivided into four concentric radial zones and anterior, central, and posterior layers based on corneal depth. Right eyes of subjects were used for statistical analysis. RESULTS: Twenty-three consecutive patients with RA and 22 healthy control subjects were included in the study. There was no significant difference with regard to age (p=0.487) or gender (p=0.514). When anterior segment parameters of both groups were compared, no significant difference was found (p>0.05). Total corneal densitometry values were statistically higher in the RA group (p=0.030). In addition, when subdivisions of the cornea were evaluated, higher densitometry values were found in the RA group in 0-2 and 2-6 mm radial zones both in the anterior and total depth (p=0.001, p=0.003 for the 0-2 mm zone and p=0.002, p=0.009 for the 2-6 mm zone). Corneal densitometry measurement was not correlated with central corneal thickness or simulated keratometry value in RA patients or healthy control subjects. CONCLUSION: The corneal densitometry values were higher in RA patients when compared to healthy control subjects, even if they had clinically clear corneas. Corneal densitometry as an objective measure of corneal clarity warrants further studies in order to ascertain its clinical relevance in RA patients.

Unusual Course of Crystalline Keratopathy in a Patient with Graft-Versus-Host Disease.

We present a case of infectious crystalline keratopathy in a patient with Graft-versus-Host disease (GVHD) who developed satellite fungal keratitis. A 51-year-old man was referred for bilateral total persistent corneal epithelial defects with severe dry eye. Although persistent epithelial defect healed with medical therapy, he developed stromal keratitis with satellite lesions confirmed to be secondary to Candida albicans. After three months of antifungal treatment and debridement, improvement of the infiltrates was obtained. Crystalline keratopathy is an important clinical entity which may develop due to several causes. The microbial causes include not only bacteria but fungi as well. Careful investigation must be performed, especially for immune-compromised patients, in order to provide appropriate and timely treatment.

Coaxial, microcoaxial, and biaxial microincision cataract surgery: prospective comparative study.

PURPOSE: To compare the intraoperative and postoperative results of 3 phacoemulsification techniques. SETTING: Atatürk Training and Research Hospital, 2nd Ophthalmology Department, Ankara, Turkey. METHODS: In this prospective randomized study, patients had standard coaxial (2.8 mm incisions), microcoaxial (2.2 mm incisions), or biaxial microincision (1.2 to 1.4 mm trapezoidal incisions) phacoemulsification. Intraoperative phaco parameters and total surgical time were measured and complications recorded. Postoperative visual acuity improvement, pachymetric differences, and surgically induced astigmatism (SIA) results were compared. RESULTS: Each group comprised 45 eyes. There were no significant differences between the 3 groups in demographic, morphologic, or preoperative surgical data. The mean effective phaco time was 2.56 seconds +/- 2.46 (SD) in the standard coaxial group, 1.98 +/- 1.91 seconds in the microcoaxial group, and 1.29 +/- 1.85 seconds in the biaxial microincision group (P<.05). The mean total surgical time was 14.48 +/- 4.21 minutes, 13.01 +/- 3.66 minutes, and 18.79 +/- 6.58 minutes, respectively (P<.01), and the mean measured final incision size was 2.83 +/- 0.11 mm, 2.26 +/- 0.07 mm, and 1.89 +/- 0.21 mm, respectively. The mean SIA 90 days postoperatively was 0.46 diopter (D), 0.24 D, and 0.13 D, respectively (P<.01). There was no statistically significant difference in the complication rate, visual acuity gain, or pachymetric change between the groups (P>.05). CONCLUSIONS: All 3 techniques were reliable, functional, and effective, yielding good visual outcomes and low phaco parameters and complication rates. Biaxial microincision surgery, with the smallest incisions, induced less astigmatism and reduced all intraoperative phaco parameters except total surgical time.