The Shape of the Ganglion Cell plus Inner Plexiform Layers of the Normal Human Macula

PURPOSE. To use surfaces generated by two-dimensional penalized splines (2D P-splines) to characterize the shape of the macular ganglion cell plus inner plexiform layers (GCLþIPL) in a group of normal humans. METHODS. Macular images of the right eyes of 23 normal subjects ranging in age from 18 to 75 years were obtained with spectral-domain optical coherence tomography (SD-OCT). The thickness of GCLþIPL was determined by manual segmentation, areas with blood vessels were removed, and the resulting maps were fit by smooth surfaces in polar coordinates centered on the fovea. RESULTS. Smooth surfaces based on 2D P-splines could precisely represent GCLþIPL thickness data, with errors comparable to the axial resolution of the SD-OCT instrument. Metrics were developed for the size, shape, and slope of the edge of the foveal depression and size and shape of the surrounding macular ridge. The slope of the foveal edge was negatively correlated with foveal size (r ¼À0.60). The size of the macular ridge was positively correlated with foveal size (r ¼ 0.75), with a slope near unity (0.90 6 0.18). The centroids of the foveal edge and macular ridge clustered near the foveal center. The foveal edge and macular ridge were well fit by ellipses. The mean GCLþIPL thickness formed an elliptical annulus elongated by approximately 30% in the horizontal direction. CONCLUSIONS. The methods developed here provide precise characterization of retinal layers for the study of glaucoma, foveal development, and other applications. (Invest Ophthalmol Vis Sci. 2012;53:7412-7420

Variance Reduction in a Dataset of Normal Macular Ganglion Cell Plus Inner Plexiform Layer Thickness Maps with Application to Glaucoma Diagnosis

To examine the similarities and differences in the shape of the macular ganglion cell plus inner plexiform layers (GCL+IPL) in a healthy human population, and seek methods to reduce population variance and improve discriminating power

Inhibitor-bound complexes of dihydrofolate reductase-thymidylate synthase from Babesia bovis

Structural characterization of the bifunctional enzyme dihydrofolate reductase-thymidylate synthase from B. bovis in the apo state and complexed with antifolate inhibitors in both enzymatic active sites is reported

Multiorgan MRI findings after hospitalisation with COVID-19 in the UK (C-MORE): a prospective, multicentre, observational cohort study

Introduction: The multiorgan impact of moderate to severe coronavirus infections in the post-acute phase is still poorly understood. We aimed to evaluate the excess burden of multiorgan abnormalities after hospitalisation with COVID-19, evaluate their determinants, and explore associations with patient-related outcome measures. Methods: In a prospective, UK-wide, multicentre MRI follow-up study (C-MORE), adults (aged ≥18 years) discharged from hospital following COVID-19 who were included in Tier 2 of the Post-hospitalisation COVID-19 study (PHOSP-COVID) and contemporary controls with no evidence of previous COVID-19 (SARS-CoV-2 nucleocapsid antibody negative) underwent multiorgan MRI (lungs, heart, brain, liver, and kidneys) with quantitative and qualitative assessment of images and clinical adjudication when relevant. Individuals with end-stage renal failure or contraindications to MRI were excluded. Participants also underwent detailed recording of symptoms, and physiological and biochemical tests. The primary outcome was the excess burden of multiorgan abnormalities (two or more organs) relative to controls, with further adjustments for potential confounders. The C-MORE study is ongoing and is registered with ClinicalTrials.gov, NCT04510025. Findings: Of 2710 participants in Tier 2 of PHOSP-COVID, 531 were recruited across 13 UK-wide C-MORE sites. After exclusions, 259 C-MORE patients (mean age 57 years [SD 12]; 158 [61%] male and 101 [39%] female) who were discharged from hospital with PCR-confirmed or clinically diagnosed COVID-19 between March 1, 2020, and Nov 1, 2021, and 52 non-COVID-19 controls from the community (mean age 49 years [SD 14]; 30 [58%] male and 22 [42%] female) were included in the analysis. Patients were assessed at a median of 5·0 months (IQR 4·2–6·3) after hospital discharge. Compared with non-COVID-19 controls, patients were older, living with more obesity, and had more comorbidities. Multiorgan abnormalities on MRI were more frequent in patients than in controls (157 [61%] of 259 vs 14 [27%] of 52; p<0·0001) and independently associated with COVID-19 status (odds ratio [OR] 2·9 [95% CI 1·5–5·8]; padjusted=0·0023) after adjusting for relevant confounders. Compared with controls, patients were more likely to have MRI evidence of lung abnormalities (p=0·0001; parenchymal abnormalities), brain abnormalities (p<0·0001; more white matter hyperintensities and regional brain volume reduction), and kidney abnormalities (p=0·014; lower medullary T1 and loss of corticomedullary differentiation), whereas cardiac and liver MRI abnormalities were similar between patients and controls. Patients with multiorgan abnormalities were older (difference in mean age 7 years [95% CI 4–10]; mean age of 59·8 years [SD 11·7] with multiorgan abnormalities vs mean age of 52·8 years [11·9] without multiorgan abnormalities; p<0·0001), more likely to have three or more comorbidities (OR 2·47 [1·32–4·82]; padjusted=0·0059), and more likely to have a more severe acute infection (acute CRP >5mg/L, OR 3·55 [1·23–11·88]; padjusted=0·025) than those without multiorgan abnormalities. Presence of lung MRI abnormalities was associated with a two-fold higher risk of chest tightness, and multiorgan MRI abnormalities were associated with severe and very severe persistent physical and mental health impairment (PHOSP-COVID symptom clusters) after hospitalisation. Interpretation: After hospitalisation for COVID-19, people are at risk of multiorgan abnormalities in the medium term. Our findings emphasise the need for proactive multidisciplinary care pathways, with the potential for imaging to guide surveillance frequency and therapeutic stratification

The Shape of the Ganglion Cell plus Inner Plexiform Layers of the Normal Human Macula

PURPOSE. To use surfaces generated by two-dimensional penalized splines (2D P-splines) to characterize the shape of the macular ganglion cell plus inner plexiform layers (GCL+IPL) in a group of normal humans. METHODS. Macular images of the right eyes of 23 normal subjects ranging in age from 18 to 75 years were obtained with spectral-domain optical coherence tomography (SD-OCT). The thickness of GCL+IPL was determined by manual segmentation, areas with blood vessels were removed, and the resulting maps were fit by smooth surfaces in polar coordinates centered on the fovea. RESULTS. Smooth surfaces based on 2D P-splines could precisely represent GCL+IPL thickness data, with errors comparable to the axial resolution of the SD-OCT instrument. Metrics were developed for the size, shape, and slope of the edge of the foveal depression and size and shape of the surrounding macular ridge. The slope of the foveal edge was negatively correlated with foveal size (r = −0.60). The size of the macular ridge was positively correlated with foveal size (r = 0.75), with a slope near unity (0.90 ± 0.18). The centroids of the foveal edge and macular ridge clustered near the foveal center. The foveal edge and macular ridge were well fit by ellipses. The mean GCL+IPL thickness formed an elliptical annulus elongated by approximately 30% in the horizontal direction. CONCLUSIONS. The methods developed here provide precise characterization of retinal layers for the study of glaucoma, foveal development, and other applications

Altered F-actin distribution in retinal nerve fiber layer of a rat model of glaucoma

Glaucoma damages the retinal nerve fiber layer (RNFL). The purpose of this study was to investigate the distribution in RNFL of axonal F-actin, a cytoskeletal component, under the development of glaucoma. Intraocular hypertension was induced in a rat model by translimbal laser photocoagulation of the trabecular meshwork. The retinas of control and treated eyes were obtained after different exposures to elevated IOP. Nerve fiber bundles were identified by fluorescent phalloidin staining of F-actin. Nuclei of cell bodies were identified by DAPI fluorescent counterstain. F-actin distribution in whole-mounted retinas was examined by confocal microscopy. En face and cross-sectional images of RNFL were collected around the optic nerve head (ONH). F-actin in normal RNFL was intensely and uniformly stained. In glaucomatous retina, F-actin staining was not uniform within bundles and total loss of F-actin staining was found in severely damaged areas. Altered F-actin often occurred near the ONH in bundles that appeared normal more peripherally. Both alteration and total loss of F-actin were found most often in dorsal retina. In normal RNFL, F-actin is rich and approximately uniformly distributed within nerve fiber bundles. Elevated IOP changes F-actin distribution in RNFL. Topographic features of F-actin alteration suggest that F-actin near the ONH is more sensitive to glaucomatous damage. The alteration pattern also suggests an ONH location for the glaucomatous insult in this rat model

Directional and spectral reflectance of the rat retinal nerve fiber layer

PURPOSE. TO measure and describe the reflectance properties of a mammalian retinal nerve fiber layer (RNFL) and to determine the mechanisms responsible for the RNFL reflectance. METHODS. An isolated rat retina suspended across a slit in a black membrane and mounted in a black perfusion chamber provided high quality images of the RNFL. Imaging microreflectometry was used to measure RNFL reflectance at wavelengths from 400 nm to 830 nm and as a function of illumination angle. RESULTS. The directional reflectance of rat RNFL at all wavelengths was consistent with the theory of light scattering by cylinders; each nerve fiber bundle scattered light into a conical sheet coaxial with the bundle. There was no evidence of a noncylindrical component at any wavelength. Measured reflectance spectra were consistent between animals, similar to ones previously measured in macaque, and varied with scattering angle. All spectra could be described by a twomechanism cylindrical scattering model with three free parameters. CONCLUSIONS. At all wavelengths the reflectance of rat RNFL arises from light scattering by cylindrical structures. The highly directional nature of this reflectance can be an important source of measurement variability in clinical assessment of the RNFL. The reflectance spectra reveal a combination of mechanisms: At wavelengths shorter than ~570 nm the reflectance comes from cylinders with diameters much smaller than the wavelength, but at wavelengths longer than ~680 nm the reflectance comes from cylinders with effective diameters of 350 nm to 900 nm. (Invest Ophthalmol Vis Set. 1999;40:639-647) T he retinal nerve fiber layer (RNFL) in humans comprises bundles of unmyelinated ganglion cell axons running just under the surface of the retina. The RNFL is damaged in glaucoma and other diseases of the optic nerve, and various optical methods to assess the RNFL are being developed as aids to clinical diagnosis and management. Understanding the optical properties of the RNFL can help reduce the variability of assessment methods and improve their ability to detect damage or progression of damage. In addition, identification of the mechanism or mechanisms responsible for the optical properties of the RNFL will enhance the interpretation of clinical measurements. Considerable evidence suggests that optically the RNFL behaves as a collection of approximately parallel cylinders. The RNFL in humans and in macaques exhibits linear birefringence parallel to the direction of nerve fiber bundles 12 and proportional to RNFL thickness. 3 This is thought to be form birefringence (birefringence due to closely spaced parallel structures immersed in a medium with a different refractive index). 6 ' 7 (See the Methods section and 9 For A greater than 560 nm the spectrum flattens, although the high spatially nonuniform background reflectance of the retinal pigment epithelium and choroid makes this feature uncertain. 9 The above evidence is limited in that the reflectance data are confined mostly to short wavelengths and amphibian retina. Although the data implicate microtubules as one RNFL reflectance mechanism, 8 the spectral flattening seen above 560 nm in the macaque 9 may indicate that another mechanism operates at long wavelengths, in the mammalian retina, or both. To overcome these limits, we used a recently developed preparation of isolated rat retina 10 to study the directional and spectral reflectance of the mammalian RNFL. We found that the RNFL reflectance arises from light scattering by cylinders at all wavelengths and that RNFL reflectance can be described by a simple model incorporating two cylindrical mechanisms

Theoretical model of the polarization properties of the retinal nerve fiber layer in reflection

In several optical technologies for glaucoma diagnosis, polarized light is used to assess the retinal nerve fiber layer (RNFL) of the eye. For better understanding of the polarization properties of the RNFL, it was modeled as a thick birefringent slab containing parallel light-scattering cylinders, and the Mueller matrix for reflectance was derived. The model predicts that (1) the RNFL reflectance has weak intrinsic diattenuation; (2) the diattenuation spectrum depends strongly on the relative refractive indices of the cylinders; (3) both scattering and birefringence contribute to retardation; and (4) the RNFL reflectance generally preserves polarization, but depolarization may be detectable for thick RNFL at short wavelengths

Stability of corneal polarization axis measurements for scanning laser polarimetry

Corneal polarization axis (CPA) has been reported to affect retardation measurements obtained with scanning laser polarimetry. The purpose of this investigation was to evaluate the longitudinal stability of CPA measurements. Prospective, noncomparative case series. Persons with normal corneas were enrolled; eyes with less than 1 year of follow-up from the initial CPA measurement were excluded. We constructed a noninvasive slit-lamp–mounted device incorporating two crossed linear polarizers and an optical retarder to measure the slow axis of corneal birefringence, or CPA. Corneal polarization axis measurements. Seventy-one eyes of 40 individuals (23 female, 17 male) were enrolled in this investigation (mean age, 42.9 ± 13.6 years; range, 22–85 years). Initial CPA measurements (mean, 24.0 ± 18.0° nasally downward; range, 67° downward to 13° nasally upward) were strongly associated (R 2 = 0.88; P < 0.0001) with repeat CPA measurements (mean, 20.9 ± 14.6° nasally downward; range, 59° nasally downward to 14° nasally upward). The mean change in CPA was 4.1 ± 3.2° (range, 0–13°). Corneal polarization axis stability was statistically associated with the mean (initial and repeat) CPA (R 2 = 0.1; P = 0.009), but not associated with age (R 2 = 0.0003; P = 0.9) or gender (R 2 = 0.03; P = 0.2). Corneal polarization axis measurements have good 1-year stability. These data suggest that CPA should not contribute significantly to longitudinal measurements of retinal nerve fiber layer thickness obtained with scanning laser polarimetry

Microtubules contribute to the birefringence of the retinal nerve fiber layer

The retinal nerve fiber layer (RNFL) exhibits birefringence that is due to the oriented cylindrical structure of the ganglion cell axons. Possible birefringent structures include axonal membranes, microtubules (MTs), and neurofilaments. MTs are generally assumed to be a major contributor, but this has not been demonstrated. In this study, the MT depolymerizing agent colchicine was used to evaluate the contribution of MTs to RNFL birefringence. Retinal nerve fiber bundles of isolated rat retina were observed through an imaging polarimeter set near extinction. Images were taken over an extended period. During baseline, the tissue was perfused with a physiological solution. During a treatment period, the solution was switched either to a control solution identical with the baseline solution or to a similar solution containing colchicine. The contrast of nerve fiber bundles was used to follow change of RNFL birefringence over time. When imaged by the polarimeter, birefringent retinal nerve fiber bundles appeared as either bright or dark stripes. Bundles displayed as bright stripes were used to follow changes in retardance. The contrast of nerve fiber bundles was stable in control experiments. However, in treatment experiments, bundles were bright during the baseline period, but the contrast of bundles decreased rapidly when the colchicine solution was applied; bundles were barely visible after 30 minutes of treatment. After 70 minutes, the bundle contrast was close to zero at all wavelengths studied (440-780 nm). MTs make a significant contribution to RNFL birefringence. The decrease of RNFL birefringence in glaucoma may indicate a loss of MTs