Corneal tomographic changes during corneal rigid gas-permeable contact lens wear in keratoconic eyes

2020 ◽  
pp. bjophthalmol-2020-317057
Author(s):  
Shizuka Koh ◽  
Ryota Inoue ◽  
Naoyuki Maeda ◽  
Yoshinori Oie ◽  
Vishal Jhanji ◽  
...  
Keyword(s):  
Contact Lenses ◽  
Amplitude Ratio ◽  
Anterior Segment ◽  
Three Dimensional ◽  
Biomechanical Properties ◽  
Corneal Surface ◽  
Surface Flattening ◽  
Contact Lens Wear ◽  
Fourier Harmonic ◽  
The Difference

Background/AimsWe aimed to investigate the refractive changes in the posterior corneal surface in keratoconus (KC) associated with wearing spherical corneal rigid gas-permeable contact lenses (corneal GPs) with apical touch or three-point touch fitting and the effect of spherical corneal GPs on corneal biomechanics.MethodsPatients with KC wearing corneal GPs every day without facing complications were enrolled as a single group. Corneal tomographic data were obtained using a three-dimensional anterior segment optical coherence tomography from the same eye with and without corneal GPs. Dioptric data from the central 3-mm zone of the posterior corneal surface were decomposed into spherical, regular astigmatism, asymmetry and higher-order irregularity components using Fourier harmonic analysis. The corneal biomechanical indices were deformation amplitude ratio within 2 mm, integrated radius, stiffness parameter at first applanation and linear Corvis Biomechanical Index. Correlations between the difference in Fourier indices with and without corneal GPs and the corneal biomechanical parameters were analysed.ResultsThirty-two eyes of 32 patients with KC were enrolled. Spherical, regular astigmatism and asymmetry components were significantly smaller with corneal GP wear than without the wear (all p<0.001). All biomechanical indices were significantly correlated with the difference in the spherical components with and without corneal GPs.ConclusionCorneal biomechanical properties of KC were correlated with posterior corneal surface flattening induced by wearing corneal GPs on the spherical components. This effect is greater in biomechanically weaker corneas.

scholarly journals Impact of Rigid Gas Permeable Contact Lenses Removal on Anterior and Posterior Corneal Surfaces in Keratoconus Patients

2019 ◽  
Author(s):  
Motohiro Itoi ◽  
Koji Kitazawa ◽  
Hisayo Higashihara ◽  
Chie Sotozono
Keyword(s):  
Contact Lens ◽  
Contact Lenses ◽  
Corneal Thickness ◽  
Anterior Segment ◽  
Corneal Surface ◽  
Contact Lens Wear ◽  
Surface Areas ◽  
The Impact ◽  
Lens Wear ◽  
Anterior Posterior

AbstractPurposeTo evaluate the impact of removal of rigid gas-permeable (RGP) contact lenses on the anterior and posterior cornea surfaces of eyes with keratoconus.MethodsEight eyes of 8 patients with keratoconus (KC) (age 34.3 ± 15.3 years; range 19–60 years) were enrolled. Anterior segment optical coherence tomography (AS-OCT) was performed at 1, 5, 10, 20, and 60 minutes after the patients removed their RGP contact lenses. Measurements included anterior and posterior best-fit sphere (BFS); elevation values and corneal surface areas; corneal thickness at the thinnest point; and the anterior-posterior ratio of the corneal surface (As/Ps) between 1 minute and 60 minutes after RGP contact lens removal.ResultsAnterior and posterior elevation values and corneal surface areas showed significant increases, whereas anterior and posterior BFS and central corneal thickness decreased significantly (P < 0.01) between 1 minute and 60 minutes after RGP contact lens removal. No statistically significant differences were found in the As/Ps ratio during the first hour after suspending RGP contact lens wear.ConclusionsWe found that the patients with keratoconus experienced significant changes in both the anterior and posterior corneal shape for 60 minutes after removal of RGP contact lenses.

scholarly journals A Review of Limbal Stem Cell Deficiency

2019 ◽  
Vol 2 (1) ◽  
pp. e4-e11
Author(s):  
John E. Conto
Keyword(s):  
Stem Cell ◽  
Contact Lenses ◽  
Systemic Disease ◽  
Anterior Segment ◽  
Treatment Strategies ◽  
Limbal Stem Cell Deficiency ◽  
Contact Lens Wear ◽  
Limbal Stem Cell Transplantation ◽  
Limbal Stem Cell ◽  
Amniotic Membranes

Limbal stem cell deficiency (LSCD) can be secondary to multiple etiologies including contact lens wear, chemical or thermal trauma, and systemic disease, any of which can result in the reduction of the number of stem cells or their decreased functionality. Primary LSCD is seen with a variety of congenital anterior segment disorders. Often LSCD can be stabilized and timely diagnosis is the key. The use of topical corticosteroids and artificial tear lubricants, along with treatment of any underlying conditions, and discontinuation of contact lenses are important initial treatment strategies. Advance treatments include amniotic membranes, limbal stem cell transplantation and keratoprostheses.

scholarly journals A new approach for quantifying epithelial and stromal thickness changes after orthokeratology contact lens wear

2021 ◽  
Vol 8 (12) ◽  
Author(s):  
Ziying Ran ◽  
Joshua Moore ◽  
Fan Jiang ◽  
Hongmei Guo ◽  
Ashkan Eliasy ◽  
...  
Keyword(s):  
Corneal Epithelium ◽  
Contact Lenses ◽  
Automatic Segmentation ◽  
Central Area ◽  
Radius Of Curvature ◽  
Corneal Surface ◽  
Contact Lens Wear ◽  
Thickness Profile ◽  
Before And After ◽  
Lens Wear

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0–2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2–5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

scholarly journals Applications of Scheimpflug Imaging in Glaucoma Management: Current and Potential Applications

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Alexander T. Nguyen ◽  
Tiffany Liu ◽  
Ji Liu
Keyword(s):  
Intraocular Pressure ◽  
Image Reconstruction ◽  
Central Corneal Thickness ◽  
Corneal Thickness ◽  
Anterior Segment ◽  
Three Dimensional ◽  
Biomechanical Properties ◽  
Scheimpflug Imaging ◽  
Potential Applications ◽  
Corneal Biomechanical Properties

Scheimpflug photography is the basis for a variety of imaging devices that are highly versatile. The applications of Scheimpflug imaging are wide in scope, spanning from evaluation of corneal ectasia to quantifying density in nuclear sclerotic cataracts. The potential uses for Scheimpflug-based devices are expanding and a number of them are relevant in glaucoma. In particular, they can provide three-dimensional image reconstruction of the anterior segment which includes assessment of the iridocorneal angle. Photographic analyses allow also for a noncontact method of estimating central corneal thickness (CCT) and intraocular pressure (IOP), as well as the study of various corneal biomechanical properties, which may be useful for stratifying glaucoma risk.

scholarly journals Effect of Pterygium Removal Combined with Conjunctival Autograft on Corneal Parameters in Swept-Source Imaging

2022 ◽  
Vol 11 (2) ◽  
pp. 329
Author(s):  
Marta P. Wiącek ◽  
Monika Kuśmierz-Wojtasik ◽  
Bogna Kowalska ◽  
Anna Machalińska
Keyword(s):  
Anterior Segment ◽  
Three Dimensional ◽  
Corneal Topography ◽  
Corneal Surface ◽  
Source Imaging ◽  
Swept Source ◽  
Eye Examination ◽  
Pterygium Excision ◽  
Oct Imaging

Background: Both pterygium ingrowth and excision determine alterations in corneal topography. The aim of this study was to evaluate the influence of pterygium removal combined with conjunctival autografts in addition to the use of human fibrin tissue glue on changes in corneal parameters as measured by 3-D swept-source anterior segment optical coherence tomography (AS-OCT) imaging. Methods: Sixteen eyes (16 patients) with pterygium that qualified for surgical treatment were enrolled in this study. Eye examination, slit lamp, and 3-D AS-OCT (CASIA 2) assessment were performed before the surgery and 7 days, 1 month, and 6 months after pterygium excision. Topographic parameters of both anterior and posterior surfaces of the cornea were analysed at each follow-up visit. Results: The gradual decrease in total astigmatism power from preoperative median 2.75 (6.15) D to 1.2 (1.1) D at 6-month follow-up (p = 0.034) was noted from the day 7 visit. Values were strongly influenced by variations of anterior cornea astigmatism. In contrast, a gradual total HOA reduction at the 1-month (from median 0.79 (1.3) D to 0.44 (0.27) D; p = 0.038) and at 6-month visits (0.25 (0.09); p = 0.001) was observed. Similarly, values were strongly influenced by variations of the anterior. Additionally, total average keratometry values increased from preoperative 44.05 (2.25) D to 44.6 (1.9) (p = 0.043) 1 month after the surgery. Conclusions: Significant steepening of the anterior cornea and a reduction in both astigmatism and HOA were observed after pterygium excision. The anterior corneal surface was an essential component of the total postoperative corneal topography values. Three-dimensional swept-source AS-OCT imaging seems to be a valuable tool for monitoring both the progression of the disease and postoperative effects in pterygium eyes.

scholarly journals Corneal biomechanical parameters in keratoconus eyes with abnormal elevation on the back corneal surface only versus both back and front surfaces

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohammad-Reza Sedaghat ◽  
Hamed Momeni-Moghaddam ◽  
Cynthia J. Roberts ◽  
Nasim Maddah ◽  
Renato Ambrósio ◽  
...  
Keyword(s):  
Amplitude Ratio ◽  
Anterior Segment ◽  
Front Surface ◽  
Back Surface ◽  
Lower Grade ◽  
Corneal Surface ◽  
Corvis St ◽  
Epithelium Thickness ◽  
Biomechanical Parameters ◽  
Group 1

AbstractCorneal biomechanical parameters were compared in 100 keratoconus eyes with abnormal elevation on the back corneal surface only (group 1), versus both the back and front surfaces (group 2). Scheimpflug tomography with Pentacam HR, corneal biomechanical assessments using Corvis ST and Ocular Response Analyzer (ORA) and corneal epithelium thickness maps using anterior segment optical coherence tomography were assessed. There were no significant differences in the IOP measured using Corvis ST and ORA, age or sex between the two groups. Statistically significant differences were found in all corneal shape parameters and all new parameters of Corvis ST: corneal stiffness parameter at first applanation (SP-A1), integrated inverse radius (IR) and deformation amplitude ratio (DAR)) between groups (p < 0.001). The classic parameters of ORA including corneal hysteresis (CH) and corneal resistance factor (CRF) were about 1.00 mmHg higher in group 1 (p < 0.001). In conclusion, keratoconus eyes with abnormal elevation limited to the back corneal surface have lower grade, stiffer corneal biomechanical parameters and less asymmetric shape. This is consistent with progressive biomechanical weakening from the first detectable back surface elevation to manifestation on the front surface as the severity overwhelms the ability of the epithelium to compensate.

Defocus ramp correction in spot-scan imaging

1992 ◽  
Vol 50 (1) ◽  
pp. 130-131
Author(s):  
Kenneth H. Downing
Keyword(s):  
Computer Control ◽  
Three Dimensional ◽  
Sufficient Accuracy ◽  
Objective Lens ◽  
Electron Crystallography ◽  
Contrast Transfer Function ◽  
Tilt Axis ◽  
Specimen Height ◽  
The Difference ◽  
Envelope Functions

Three-dimensional structures of a number of samples have been determined by electron crystallography. The procedures used in this work include recording images of fairly large areas of a specimen at high tilt angles. There is then a large defocus ramp across the image, and parts of the image are far out of focus. In the regions where the defocus is large, the contrast transfer function (CTF) varies rapidly across the image, especially at high resolution. Not only is the CTF then difficult to determine with sufficient accuracy to correct properly, but the image contrast is reduced by envelope functions which tend toward a low value at high defocus.We have combined computer control of the electron microscope with spot-scan imaging in order to eliminate most of the defocus ramp and its effects in the images of tilted specimens. In recording the spot-scan image, the beam is scanned along rows that are parallel to the tilt axis, so that along each row of spots the focus is constant. Between scan rows, the objective lens current is changed to correct for the difference in specimen height from one scan to the next.

Therapeutic effect of toric contact lenses in patients with an irregular corneal surface

2020 ◽  
pp. 54-56
Author(s):  
B.I. Esergepova ◽  
◽  
G.K. Mukhataeva ◽  
M. Makenbaeva ◽  
◽  
...  
Keyword(s):  
Therapeutic Effect ◽  
Contact Lenses ◽  
Corneal Surface

The iron content of iron superoxide dismutase: determination by anomalous scattering

1983 ◽  
Vol 218 (1210) ◽  
pp. 119-126 ◽  
Keyword(s):  
Superoxide Dismutase ◽  
Iron Content ◽  
Three Dimensional ◽  
Anomalous Scattering ◽  
Total Iron Content ◽  
Iron Site ◽  
Iron Superoxide Dismutase ◽  
Density Map ◽  
The Difference ◽  
Electron Density Map

The number of iron atoms in the dimeric iron-containing superoxide dismutase from Pseudomonas ovalis and their atomic positions have been determined directly from anomalous scattering measurements on crystals of the native enzyme. To resolve the long-standing question of the total amount of iron per molecule for this class of dismutase, the occupancy of each site was refined against the measured Bijvoet differences. The enzyme is a symmetrical dimer with one iron site in each subunit. The iron position is 9 ņ from the intersubunit interface. The total iron content of the dimer is 1.2±0.2 moles per mole of protein. This is divided between the subunits in the ratio 0.65:0.55; the difference between them is probably not significant. Since each subunit contains, on average, slightly more than half an iron atom we conclude that the normal state of this enzyme is two iron atoms per dimer but that some of the metal is lost during purification of the protein. Although the crystals are obviously a mixture of holo- and apo-enzymes, the 2.9 Å electron density map is uniformly clean, even at the iron site. We conclude that the three-dimensional structures of the iron-bound enzyme and the apoenzyme are identical.

Sign in / Sign up

Export Citation Format

Share Document