Colleen Riley

Large‐scale volcanic eruptions produce fine ash (<200 μm) which has a long atmospheric residence time (1 hour or more) and can be transported great distances from the volcanic source, thus, becoming a hazard to aircraft and public health. Ash particles have irregular shapes, so data on particle shape, size, and terminal velocities are needed to understand how the irregular‐shaped particles affect transport processes and radiative transfer measurements. In this study, a methodology was developed to characterize particle shapes, sizes, and terminal velocities for three ash samples of different compositions. The shape and size of 2500 particles from (1) distal fallout (∼100 km) of the 14 October 1974 Fuego eruption (basaltic), (2) the secondary maxima (∼250 km) of the 18 August 1992 Spurr eruption (andesitic), and (3) the Miocene Ash Hollow member, Nebraska (rhyolitic) were measured using image analysis techniques. Samples were sorted into 10 to 19 terminal velocity groups (0.6–59.0 cm/s) using an air elutriation device. Grain‐size distributions for the samples were measured using laser diffraction. Aspect ratio, feret diameter, and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity. These measurement values show particle shape differs greatly from a sphere (commonly used in models and algorithms). The diameters of ash particles were 10–120% larger than ideal spheres at the same terminal velocity, indicating that irregular particle shape greatly increases drag. Gas‐adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry, indicating that particle shapes are highly irregular. Correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values.

PURPOSE: Many soft contact lens wearers have symptoms or signs that compromise successful lens wear. This study estimated the prevalence of problems in current wearers of soft contact lenses and tested the effect of refitting patients with senofilcon A silicone hydrogel lenses (ACUVUE Oasys). METHODS: Prevalence was estimated from 1,092 current lens wearers for frequent or constant discomfort or dryness, at least 2 hours of uncomfortable wear, at least grade 2 limbal or bulbar hyperemia (0-4), or at least grade 3 corneal staining (0-15). In the second part of the study, 112 of the 564 wearers classified as problem patients were refitted with senofilcon A lenses and reassessed 2 weeks later. RESULTS: Fifty-two percent (564 of 1,092) had some qualifying criteria, with dryness reported by 23%, discomfort by 13%, and at least 2 hours of uncomfortable wear by 27%. Six percent of subjects had qualifying limbal hyperemia; 10% had bulbar hyperemia; and 12% had corneal staining. After refitting 112 problem patients, 75% had less dryness; 88% had better comfort (P<0.0001 each); and 76% had fewer uncomfortable hours of wear (P=0.004). Although the average wearing time was unchanged, comfortable wearing time increased significantly (10.4 to 11.6 hours) (P=0.004). All (35 of 35) eyes with qualifying limbal hyperemia before the refit also improved (P<0.0001), as did 80% (40 of 50) of those with bulbar hyperemia (P<0.0001) and 76% (26 of 34) of those with corneal staining (P=0.005). CONCLUSIONS: Most soft lens wearers encounter clinically significant signs or symptoms with their current contact lenses. Refitting with new-generation silicone hydrogel lenses (senofilcon A) can alleviate some of these common problems.

PURPOSE: The multicenter Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a prospective, observational study of 1209 keratoconus patients. We report methods to define incident corneal scarring and baseline factors predictive of incident corneal scarring in nonsurgical eyes of CLEK Study keratoconus patients through their fifth year of follow-up. METHODS: Of the 1,209 patients, 878 patients with at least one unscarred cornea at baseline were included in this study. The cumulative 5-year incidence of scarring is defined as the proportion of patients who developed central corneal opacification as detected by a clinician examining the patient with a slit-lamp biomicroscope and by masked readings of corneal photographs at the CLEK Photography Reading Center. Logistic regression analysis was used to test for relationships between baseline factors and incident corneal scarring. Baseline factors analyzed included age, sex, race, atopic disease, contact lens wear, family history of keratoconus, corneal curvature, and central corneal fluorescein staining, among others. RESULTS: The 5-year incidence of corneal scarring was 13.7% (120 of 878) overall, 16.7% (102 of 609) for contact lens-wearing eyes, and 38.0% (46 of 121) for contact lens-wearing eyes with corneal curvature greater than 52 D. Baseline factors predictive of incident scarring included corneal curvature greater than 52 D (odds ratio [OR] = 4.79; 95% confidence interval [CI], 3.08, 7.45; P < 0.001), contact lens wear (OR = 2.50; 95% CI, 1.40, 4.76; P = 0.003), marked corneal staining (OR = 2.38; 95% CI, 1.49, 3.76; P = 0.0002), and age less than 20 years (OR = 6.34; 95% CI, 2.57, 15.00; P < 0.0001). CONCLUSIONS: Multivariate analyses of 5-year prospective data from the CLEK Study cohort showed that baseline corneal curvature, contact lens wear, corneal staining, and younger age were predictive of the development of corneal scarring. The 5-year incidence of scarring is 13.7% for the overall sample and 38.0% for those eyes with corneal curvature greater than 52 D that wore contact lenses. Contact lens wear increased the risk of incident scarring more than 2-fold. These findings suggest a causal contribution of contact lens wear to corneal scarring in keratoconus and imply that corneal scarring might be reduced by modifying the contact lens fit.

PURPOSE: To evaluate the influence of peripheral ocular topography, as evaluated by optical coherence tomography (OCT), compared with traditional measures of corneal profile using keratometry and videokeratoscopy, on soft contact lens fit. METHODS: Ocular surface topography was analyzed in 50 subjects aged 22.8 years (SD ±5.0) using videokeratoscopy (central keratometry, corneal height, and shape factor) and OCT to give both full sagittal cross-sections of the cornea and cross-sections of the corneoscleral junctions. Corneoscleral junction angle, corneal diameter, corneal sagittal height, and scleral radius were analyzed from the images. Horizontal visible iris diameter and vertical palpebral aperture were analyzed from digital slit lamp images. Lens fit was graded after 30 minutes wear of a -2.50 D commercially available standard hydrogel (etafilcon A, modulus 0.30 MPa) and silicone hydrogel (galyfilcon A, 0.43 MPa) design of similar geometries (8.30-mm base curve, 14.0-mm diameter). RESULTS: The mean horizontal corneal diameter was 13.39 mm (SD ±0.44). In many cases, there was a tangential transition at the corneoscleral junction. The corneoscleral shape profile analyzed from cross-sectional OCT images contributed significantly (P < 0.001) to the prediction of soft contact lens fit compared with keratometry and videokeratoscopy, accounting for up to 24% of the variance in lens movement. The fit of the stiffer material silicone hydrogel lens was better able to be predicted and was more varied than the hydrogel contact lens. CONCLUSIONS: The extra peripheral corneoscleral data gained from OCT characterization of ocular surface architecture provide valuable insight into soft contact lens fit dynamics.