Backward Light Scatter Research Articles

Associations Between Visual Functions and Severity Gradings, Corneal Scatter, or Higher-Order Aberrations in Fuchs Endothelial Corneal Dystrophy.

The purpose of this study was to investigate the associations between visual function and severity grading, corneal scatter, or higher-order aberrations (HOAs) in patients with Fuchs endothelial corneal dystrophy (FECD). This observational case series study included 49 eyes of 27 patients with FECD and 10 eyes of 10 healthy individuals. We evaluated corrected distance visual acuity (CDVA) using Landolt-C and Early Treatment Diabetic Retinopathy Study charts and contrast sensitivity using the CSV-1000E chart and CSV-1000RN letter chart. We analyzed the associations between visual function and explanatory variables, including age, modified Krachmer grade, central corneal thickness (CCT), anterior segment optical coherence tomography (AS-OCT)-based grade, HOAs, intraocular straylight, and corneal densitometry. We additionally conducted receiver operating characteristic (ROC) analysis to identify the corneal densitometry thresholds for decreased visual function. There were significant associations between visual function and the modified Krachmer grade, CCT, AS-OCT-based grade, HOAs, intraocular straylight, and corneal densitometry. A modified Krachmer grade ≥ 3 was identified as a threshold for decreased visual function. Multivariate analysis showed that corneal densitometry was significantly associated with all visual function parameters, and HOAs were significantly associated with CDVA but not with contrast sensitivity. ROC analysis revealed that corneal densitometry of the posterior layer at 0 to 2mm ≥ 10 grayscale units (GSU), was identified as a threshold for decreased visual function. HOAs, forward and backward light scatter affected visual function, with backward light scatter being the most influential. In patients with FECD, modified Krachmer grade ≥ 3 and corneal densitometry ≥ 10 GSU were thresholds for visual disturbance.

Visual Function and Functional Decline in Patients With Waterclefts.

To investigate visual function in eyes with three subtypes of waterclefts (WCs). Of patients in Kanazawa Medical University Hospital (2013-2017) and participants of Monzen Eye Study (2013-2016), 77 transparent lenses, mean age 66.7 years, and 70 eyes with only WC opacity of 70 patients, mean age 68.1 years, divided into peripheral-, central-, and total-type WC groups, were analyzed. Opacity was classified by one ophthalmologist using slit-lamp microscopy. Corrected-distance visual acuity (CDVA), contrast visual acuity (CVA), spherical equivalent (SE), astigmatism values, corneal refractive power (CP), axial length (AL), straylight, backward light scattering (BLS), and higher order aberrations (HOA) were measured and lenticular refractive power (LP) was calculated based on the values of AL, CP, and SE. Central-type WC showed significant decrease in CDVA and CVA and increase in straylight compared with control. Total-type WC showed significant decreases in CDVA, CVA, and LP, and increase in straylight, compared with control and peripheral-type WC. Total- and central-type WCs had significantly higher ocular total HOA and total-type WC had significantly higher internal total HOA than control. HOA correlated positively with CDVA (P < 0.001) and straylight (P = 0.020), and CDVA negatively with straylight in eyes with WCs (P = 0.008). Total-type WC was associated with decreased LP, causing hyperopia, decreased CDVA and higher straylight; thus, such lenticular change should be considered for surgery indication. Significant correlations between HOA and both CDVA and straylight suggested increased HOA may decrease visual function in eyes with WCs.

Assessment of Corneal Backward Light Scattering in Diabetic Patients.

To analyze corneal backward light scattering differences in patients with type 2 diabetes mellitus. We enrolled 43 eyes from 43 diabetic patients and 40 eyes from 40 healthy controls. Corneal backward light scattering was evaluated using densitometry measurements from different corneal layers and zones obtained using Scheimpflug tomography (PentacamHR). When densitometry values were divided by depth, anterior layer of diabetic corneas displayed significantly higher corneal backward light scattering values than controls (32.05, 95% confidence intervals [CI], 31.02-33.08 vs. 29.18, 95% CI, 27.60-30.76, P=0.024). Corneal densitometry measurements were also significantly higher in diabetic eyes compared with control eyes, when considered by concentric zones of total cornea in the 0 to 2 mm (21.65, 95% CI, 20.28-23.01 vs. 18.87 95% CI, 18.49-19.25, P=0.020), and anterior layer in the 0 to 2 mm (27.3, 95% CI, 25.04-29.56 vs. 22.31, 95% CI, 20.57-24.05, P<0.001), 2 to 6 mm (26.2, 95% CI, 24.99-27.41 vs. 22.4, 95% CI, 20.18-24.62, P<0.001) and 6 to 10 mm (32.19, 95% CI, 29.98-34.40 vs. 27.2, 95% CI, 25.39-29.01, P=0.022). There was excellent positive correlation between anterior total corneal densitometry measurements and duration of diabetes (r=0.802, P<0.001), although no significant correlation was observed with anterior total corneal densitometry measurements and hemoglobin A1c levels (r=0.080, P=0.621) in diabetic eyes. Backward light scattering values from the anterior layer of the cornea is greater in diabetic eyes than in controls. Anterior total corneal densitometry measurements show positive correlation with the duration of diabetes.

Methods for assessing forward and backward light scatter in patients with cataract

To compare objective methods for assessing backward and forward light scatter and psychophysical tests in patients with cataracts. Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom. Prospective case series. This study included patients scheduled for cataract surgery.Lens opacities were grouped into predominantly nuclear sclerotic, cortical, posterior subcapsular, and mixed cataracts. Backward light scatter was assessed using a rotating Scheimpflug imaging technique (Pentacam HR), forward light scatter using a straylight meter(C-Quant), and straylight using the double-pass method (Optical Quality Analysis System, point-spread function [PSF] meter). The results were correlated with visual acuity under photopic conditions as well as photopic and mesopic contrast sensitivity. The study comprised 56 eyes of 56 patients. The mean age of the 23 men and 33 women was 71years (range 48 to 84years). Two patients were excluded. Of the remaining, 15patientshad predominantly nuclear sclerotic cataracts, 13 had cortical cataracts, 11 had posterior subcapsular cataracts, and 15 had mixed cataracts. Correlations between devices were low. The highest correlation was between PSF meter measurements and Scheimpflug measurements (r=0.32). The best correlation between corrected distance visual acuity was with the PSF meter (r=0.45). Forward and backward light-scatter measurements cannot be used interchangeably. Scatter as an aspect of quality of vision was independent of acuity. Measuring forward light scatter with the straylight meter can be a useful additional tool in preoperative decision-making.

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360° rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

Ocular forward light scattering and corneal backward light scattering in patients with dry eye.

To evaluate ocular forward light scattering and corneal backward light scattering in patients with dry eye. Thirty-five eyes in 35 patients with dry eye and 20 eyes of 20 healthy control subjects were enrolled. The 35 dry eyes were classified into two groups according to whether superficial punctate keratopathy in the central 6-mm corneal zone (cSPK) was present or not. Ocular forward light scattering was quantified with a straylight meter. Corneal backward light scattering from the anterior, middle, and posterior corneal parts was assessed with a corneal densitometry program using the Scheimpflug imaging system. Both dry eye groups had significantly higher intraocular forward light scattering than the control group (both P<0.05). The dry eye group with cSPK had significantly higher values in anterior and total corneal backward light scattering than the other two groups. Moderate positive correlations were observed between the cSPK score and corneal backward light scattering from the anterior cornea (R=0.60, P<0.001) and corneal backward light scattering from the total cornea (R=0.54, P<0.001); however, no correlation was found between cSPK score and ocular forward light scattering (R=0.01, P=0.932). Ocular forward light scattering and corneal backward light scattering from the anterior cornea were greater in dry eyes than in normal eyes. Increased corneal backward light scattering in dry eye at least partially results from cSPK overlying the optical zone.

Changes in Forward and Backward Light Scatter in Keratoconus Resulting From Corneal Cross-Linking.

To study the forward and backward light scatter in keratoconic corneas before and after cross-linking. An institutional, prospective, cross-sectional study was conducted. This study includes 35 eyes of 25 patients with keratoconus scheduled for either standard corneal collagen cross-linking with riboflavin (CXL) or transepithelial corneal cross-linking (TE-CXL). A group of 26 healthy myopic eyes from 26 prerefractive patients was included as normal reference. Before and 6 months after cross-linking, forward light scatter was measured using the compensation comparison method, whereas backward light scatter was measured using Scheimpflug imaging. In keratoconic eyes, backward light scatter originating from the corneal stroma was [mean (SD)] 27.2% (8.2%) higher than in the normal eyes (P < 0.001). In the anterior stroma, this increased backscatter was significantly correlated with the maximum corneal curvature Kmax as a measure of keratoconus severity (Pearson ρ = 0.582, P = 0.003). For forward light scatter, no significant difference was seen between the normal and keratoconus groups, nor was there any correlation with keratoconus severity. After CXL, the backscatter increased significantly by [mean (SD)] 33.0% (9.5%) in the entire corneal stroma (P = 0.001), whereas for TE-CXL, no significant increase was seen. Forward scatter increased significantly by [mean (SD)] 0.10 (0.10) log units (P = 0.009) and 0.09 (0.10) log units (P = 0.003) for CXL and TE-CXL, respectively, which is near the detection limit for an average patient. Unlike TE-CXL, CXL increases the already-elevated stromal backscatter in keratoconus. Forward scatter increases equally for both techniques.

Backscattered light from the cornea before and after laser-assisted subepithelial keratectomy for myopia

To study corneal backscatter changes after laser-assisted subepithelial keratectomy (LASEK) and to search for correlations between the changes in forward and backward corneal light scatter. Antwerp University Hospital, Edegem, Belgium. Prospective interventional case series. Corneal backscatter was determined with a commercial Scheimpflug device and purpose-written image-analysis software. The mean backscatter profile and gray value distributions of the images for a 1.0 mm zone around the corneal apex were obtained preoperatively and 6 months after LASEK for myopia. This was compared with forward light scatter (or straylight) using measurements obtained with the compensation comparison method. The study enrolled 80 eyes (40 patients; mean age 34.2 years ± 10.4 [SD]). Very strong correlations were found between the backscatter profiles of right eyes and left eyes preoperatively. Hence, only right eyes were used for further calculations. The epithelial-Bowman peak of the backscatter profile decreased significantly after LASEK (mean decrease -2.2 ± 4.7 grayscale units) (P=.002, paired t test), which corresponded to the ablation of Bowman layer. Significant changes in the gray-value distribution were observed postoperatively, corresponding to the decreases in the epithelium-Bowman peak. Forward light scatter decreased significantly after LASEK (mean decrease -0.10 ± 0.13) (P<.001); however, no significant correlation with corneal backscatter was observed. The anterior part of the corneal backscatter profile decreased significantly after LASEK. A significant reduction in forward light scatter was also seen, although it was not correlated to backward light scatter.

Determination of lead in environmental water by a backward light scattering technique

An optical fiber assembly developed in our laboratory, which is based on detecting backward light scattering (BLS) signals, is now applied to detect the lead content in environmental samples. Due to effectively eliminating the interference of reflected light, this BLS signals based detection assembly can be used to determine analyte directly. In HAc–NaAc buffer medium (pH 4.8), the interaction of lead and sodium tetraphenylboron (TPB) in the presence of polyethylene glycol (PEG) yields large particles of ternary complex, resulting in strong enhanced backward light scattering (BLS) signals characterized at 371 nm. By measuring the BLS signals with the homemade optical fiber assembly coupled with a common spectrofluorometer, we found that the enhanced BLS intensity is proportional to lead content over the range of 0.03–1.0 μg ml −1 with the limit of determination (LOD) of 2.6 ng ml −1. Three artificial water samples containing various coexistent substances were detected with the recovery of 90.1–107.5%. Standard addition method was used to detect the lead content in drink tap water, and found that the lead is hardly to detect due to too low content. Prior enrichment should be made in order to detect river water samples, and it was found that the content of lead in Jialing River at Bebei Dock is about 14 ng ml −1, identical to the results using inductively coupled plasma atomic emission spectrometry (ICP-AES).

Light scattering and optical aberrations as objective parameters to predict visual deterioration in eyes with cataracts

Purpose: To predict the visual deterioration of eyes with cortical (CC) or nuclear (NC) cataract from objective data on ocular higher-order aberration (HOA) and forward (FLS) and backward light scattering (BLS). Setting: Osaka University Medical School, Osaka, Japan. Methods: Twenty-two eyes with mild NC, 41 eyes with mild CC, and 11 normal eyes were examined. Higher-order aberrations were calculated with the Zernike polynomials up to the fourth order from the values obtained by wavefront analysis using the Hartmann-Shack aberrometer. Forward light scattering was calculated from the size of the aberrometer spot images for the central 4 mm, and backward light scattering (BLS) was calculated from the optical density of the Scheimpflug images. The relationship between the area under the log contrast sensitivity function (AULCSF) curve and HOAs, FLS, and BLS was examined. Results: Area under the log contrast sensitivity function was moderately correlated with the HOAs, FLS, and BLS. Multiple linear regression analysis revealed that the AULCSF was predicted by the linear combination of these variables ( R 2=.484, P<.001). Area under the log contrast sensitivity was predicted by BLS and HOA ( R 2=.555) in the NC group and by FLS and HOAs ( R 2=.540) in the CC group. Conclusions: Loss of contrast sensitivity was predominantly due to BLS and HOA in eyes with NC and FLS and HOA in eyes with CC. Higher-order aberrations, FLS, and BLS, variables that are obtained objectively, can be used to predict quantitatively the visual deterioration in cataractous eyes.

Monitoring the Dynamics of Concentrated Suspensions by Enhanced Backward Light Scattering

The shear-induced flocculation of kaolin-polymer flocs in a stirred tank is investigated at medium to high solids concentrations (ϕ=1−10% w/w). The evolution of the average floc size is monitored by the change in intensity of laser light scattered in the 180° direction. The measurements reflect the change in particle number concentration as flocculation proceeds. As flocculation begins, coagulation dominates and the floc size increases (total particle number decreases) and then levels off at a steady state value as fragmentation becomes significant and balances coagulation. At steady state, the measurements indicate the extent of flocculation. Increasing the shear rate increases the coagulation and fragmentation rates, resulting in smaller floc sizes at steady state. Increasing the flocculant concentration increases the steady state floc size by strengthening the bonds between primary particles to resist fragmentation. At constant shear rate and flocculant concentration, increasing the solids fraction decreases the steady state floc size indicating formation of weakly bonded flocs. Flocculant mixing was the most important factor for flocculation efficiency at high solids concentrations.

Forward and backward light scatter measurements in the assessment of corneal oedema

As the cornea swells it loses its transparency, thereby increasing both forward and backward light scatter. The purpose of this study was to investigate the changes in corneal transparency by means of scatter assessment. Both forward and backward light scatter measurements were obtained from 18 normal corneas, before and after the induction of corneal oedema with sealed scleral lenses. Forward light scatter was measured at 3.5, 10 and 28 degrees, using a portable straylight meter as developed by van den Berg. Backward light scatter measurements were obtained by computerised linear scanning densitometry of Scheimpflug images using the Oxford Modular Cataract Image Analysis System. After the scleral lenses were worn, forward light scatter values increased significantly at all the three angles (3.5°: F1,17 = 65.69, P &lt; 0.001; 10° : F1,17 = 37.30, P &lt; 0.001; 28°: F1,17 = 26.66, P &lt; 0.001). Backward light scatter also increased significantly with the presence of corneal oedema (F1,17 = 3 4.80, P &lt; 0.001). A significant correlation was found between the differences on forward light scatter recorded at the different angles. However, no significant correlation was found between the increase in forward and backward scatter recorded by the two techniques. We conclude that both forward and backward light scatter can be good indicators of corneal transparency.

Forward and backward light scatter measurements in the assessment of corneal oedema

Forward and backward light scatter measurements in the assessment of corneal oedema

Forward light scatter at one month after photorefractive keratectomy.

Although it is known that backward light scatter increases transiently following most excimer laser photorefractive keratectomies (PRKs), it is not clear that there is a significant increase in forward light scatter, which is of primary concern for the patient. The object of this study was to determine if there is a significant change of forward light scatter at 1 month after (PRK) with an ablation zone diameter of 6 mm. Overlapping subsets of 24 normal myopic eyes were tested before (on the day of surgery) and 1 month after PRK, using three instruments: a Stray Light Meter (16 eyes); a Computerized Stray Light Meter (14 eyes); and a mesopic Increment Threshold-Glare Paradigm (six eyes). Differences between the two eyes before PRK were compared with the differences between the same eye before and after PRK, using repeated measured analysis of variance. In addition, increment threshold data obtained from 22 eyes after PRK were compared with those of 60 controls of the same age range and distribution by a t test. None of the statistical comparisons approached significance at the alpha = 0.05 level. Changes in light scatter as small as a factor of 1.95 (Stray Light Meter) and 1.55 (Increment Threshold-Glare Paradigm) could be detected as significant with a high power (0.8). Changes larger than a factor of 21 could be detected with a power of 0.8 for the Computerized Stray Light Meter. In these data, there is no support for the hypothesis that forward light scatter increases significantly 1 month after PRK with an ablation zone of 6 mm. Any increases in forward light scatter are unlikely to be greater than a factor of 1.5 to 2 under daytime or nighttime illumination conditions.

Light scatter changes due to corneal oedema and contact lens wear

G LARE disability can be a problem for contact lens wearers. 1-5 It is caused by a reduction in contrast of the retinal image due to a veiling luminance caused by light scatter within the eye. ~,7 Most of the early studies on glare disability in polymethylmethacrylate (PMMA) contact lens wearers found a reduction in visual performance due to light scatter caused by both epithelial and stromal oedema. 1,2 In the early stages of contact lens wear, the increased lacrimation produces osmotic stress leading to epithelial oedema, s,9 Epithelial oedema can be characterised by large increases in forward scattering of light 1° and is considered to be more visually disabling than is stromal oedema. 11,12 As adaptation to the contact lens occurs, potential epithelial osmotic stress is r educed20edematous changes in adapted lens wearers are more likely to be hypoxic in origin2 Although the main corneal change due to hypoxia is stromal oedema, any significant increases in light scatter due to hypoxia are thought to be due to small epithelial changes. ~3 Glare disability has become less of a problem with the increased use of rigid gas permeable (RGP) and hydrophilic lens materials. 14,15 Recently, Applegate and Wolff measured glare disability in hydrophilic contact lens wearers. Using a sample of five subjects they showed that disability glare was increased with contact lenses as compared to the equivalent spectacle correction. They suggested that this may be due to either the contact lens materials, lens deposits, or corneal oedema. However, a follow-up study by Applegate and Jones 4, using 12 subjects, found more variable results. Some subjects showed an increase in glare disability, some a decrease, and some no change. They concluded that glare disability is not a problem for all lens wearers and suggested that this was consistent with the clinical impressions of patients who reported glare problems. They suggest that disability glare in these subjects may be correlated to the contact lens material or the amount of lens deposit. Backward light scatter is the light scattered back from the ocular media, which can be seen using a slit-lamp. It is more important to measure forward light scatter, however, as it is forward scatter that