Corneal Apex Research Articles

New method to analyze sagittal images of upper eyelid obtained by anterior segment optical coherence tomography

ABSTRACTPurpose: To report a new method to analyze sagittal images of the upper eyelid by anterior segment optical coherence tomography (AS-OCT).Methods: Ninety subjects equally divided into young (20–39 years), middle age (40–59 years), and elderly (60–79 years) group were studied. A sagittal image of the upper eyelid was obtained by AS-OCT (CASIA2, Tomey, Japan) and the following parameters were determined: upper eyelid thickness (UET), the distance between two parallel lines tangential to the apexes of the cornea and the upper eyelid; the upper eyelid angle (UEA) was the angle formed by a line running tangential to the apex of the cornea and a line passing from the apex of the cornea to the apex of the upper eyelid; and the cross-sectional area (CSA), the area from the edge of the eyelid to a point 6 mm above the corneal apex. All parameters were compared among groups and correlation analyses were studied between age and eyelid parameters.Results: The UET was 2.09 ± 0.58 mm, 2.63 ± 1.04 mm and 2.83 ± 0.83 mm in the young, middle age and elderly group, respectively. The difference between the young and the elderly group was significant (P = 0.014). The elderly group had a significantly larger UEA than that of young group (P = 0.022). The elderly group also had significantly larger CSA than the other two groups (all P < 0.01). The age was significantly correlated with all eyelid parameters.Conclusions: AS-OCT can be used as a non-invasive and quantitative method of evaluating sagittal images of the upper eyelid.

Evaluation of corneal layers and anterior sclera in patients with primary Sjögren's syndrome.

We aimed to compare the thickness of anterior sclera, corneal layers, and pre-ocular tear film between patients with primary Sjögren's syndrome and healthy individuals. Fifty-one patients with primary Sjögren's syndrome and 41 healthy control participants were recruited in this cross-sectional and comparative study. The thickness of the pre-ocular tear film, corneal epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium were measured on the corneal apex. Anterior scleral thickness was measured at distances of 1 mm and 3 mm from the limbus. The anterior segment module of spectral-domain optical coherence tomography was used to measure thicknesses of pre-ocular tear film, corneal layers, and anterior sclera. Tear film thickness, Schirmer's test, and tear break up time values were significantly lower in the Sjögren's disease group than in the healthy controls (p<0.05). The thickness measurements of corneal layers and sclera were similar between the groups. Tear film thickness was moderately correlated with the Schirmer's test results (r=0.34, p=0.001), but there was no correlation between the Schirmer's test results and tear break up time (r=0.18, p=0.09). Pre-ocular tear film, as measured by anterior segment optical coherence tomography, was thinner in patients with primary Sjögren's syndrome than in the healthy controls. The thicknesses of corneal layers and anterior sclera were similar between the groups.

Short-Term Effects of Overnight Orthokeratology on Corneal Sensitivity in Chinese Children and Adolescents.

Purpose To assess the effects of the 3-month period of orthokeratology (OK) treatment on corneal sensitivity in Chinese children and adolescents. Methods Thirty subjects wore overnight OK lenses in both eyes for 3 months and were assessed at baseline, 1 day, 1 week, 1 month, and 3 months after the treatment. Changes in corneal sensitivity were measured by the Cochet–Bonnet (COBO) esthesiometer at the corneal apex and approximately 2 mm from the temporal limbus. Changes in refraction and corneal topography were also measured. Results Central corneal sensitivity suffered a significant reduction within the first month of the OK treatment period but returned to the baseline level at three months (F = 3.009, P=0.039), while no statistically significant difference occurred in temporal sensitivity (F = 2.462, P=0.074). The baseline of central corneal sensitivity correlated with age (r = −0.369, P=0.045). A marked change in refraction (uncorrected visual acuity, P < 0.001; spherical equivalent, P < 0.001) and corneal topographical condition (mean keratometry reading, P < 0.001; eccentricity value, P < 0.001; Surface Regularity Index, P < 0.001) occurred, but none of these measurements were correlated with corneal sensitivity. Conclusions A 3-month period OK treatment causes a reduction in central corneal sensitivity in Chinese children and adolescents but with a final recovery to the baseline level, which might be because neuronal adaptation occurred earlier in children and adolescents than in adults.

Corneal endothelium features in Fuchs' Endothelial Corneal Dystrophy: A preliminary 3D anterior segment optical coherence tomography study.

PurposeTo evaluate the feasibility of 3D anterior segment optical coherence tomography (AS-OCT) for the detection of corneal endothelial features in patients with Fuchs’ Endothelial Corneal Dystrophy (FECD).MethodsTwenty patients with clinical diagnosis of FECD (group A), and 20 control subjects (group B) were enrolled. In all patients a complete ophthalmological examination was performed, including best corrected visual acuity (BCVA), slit lamp examination for subjective grading of FECD and corneal endothelial specular microscopy. A 512x128 AS-OCT cube centered on the corneal apex was performed, and then the inner surface of the cornea was visualized and analyzed individually.ResultsOverall, the study participants were adults (mean age was 57.35 ± 8.45 years [mean ± SD] 80% female) with a BCVA ranged from 1.3 to 0 LogMAR. The OCT analysis disclosed three different patterns of the corneal endothelium (1, 2, 3) according to the signal distribution and the level of reflectivity: a homogenous, hypo-reflective surface (pattern 1); the presence of hyper-reflective orange-yellowish points (pattern 2); and a mottled appearance with a variable number of hyper-reflective areas (pattern 3). The distributions of these morphological models in the two populations were as follows: patterns 1, 2 and 3 were observed respectively in 0%, 80%, and 20% of patients in group A, and in 80%, 20% and 0% of subjects in group B. Correlation analysis unveiled a positive relationship between OCT corneal endothelium reflectivity and the clinical severity score (assessed with biomicroscopy), as well as an inverse relationship between the OCT pattern and the integrity of corneal endothelium.Conclusion3D AS-OCT is a useful tool in investigation of endothelial features and therefore may represent a valuable support in the setting of FECD diagnosis and staging.

Grundlagen der Optik

As an ophthalmologist, it is very important to know whether limited vision is caused by refractive problems or whether there is another pathology behind it. That's why refraction plays a key role at the beginning of every eye examination. Therefore, it is important to know the basic principles of optics. When fitting spherical and cylindrical lenses, it is interesting to know which properties the respective lenses have. One should also be aware of the optical paths and refraction laws when fitting spectacle lenses and prisms. In addition, when prescribing spectacle lenses, one should consider changes in the distance between corneal apex and spectacle lens and know conversions for the strength of contact lenses. Only if you have a deeper understanding of refraction and correction of refractive errors you will be able to adjust optimal vision aids for more difficult refraction conditions.

Correlation of central and peripheral keratometric parameters after corneal collagen cross-linking in keratoconus patients

To evaluate the difference in the central and peripheral keratometric parameters in patients with keratoconus after corneal collagen cross-linking (CXL). Forty-eight eyes of 32 patients (18 males, 16-28years) affected by progressive keratoconus in different stages of evolution underwent CXL using the standard epithelium-off protocol. Corneal thickness and corneal curvature before CXL and after 6 and 12 months using the Sirius tomographer were analyzed. The values of the mean corneal thickness at the corneal apex (CAT), center of the pupil (PCT), thinnest point (CTTL) and along concentric circles of 2, 4, 6, 8, 8.5, 9, 9.5 and 10mm diameter were evaluated; the values of the mean curvature at the corneal apex and at the points in which the inferior, superior, nasal and temporal meridians crossed the above-mentioned concentric circles were also evaluated. The mean preoperative values for CAT, PCT and CTTL were 461.4 ± 30.3, 475.3 ± 30.5 and 441 ± 32.0, respectively. The values after 12months of CXL were 444.6 ± 36.2, 451.6 ± 36.7 and 418.2 ± 41.4. The peripheral corneal thickness at the eight points ranged from 479 to 733 preoperatively. At 12-month post-CXL, the values ranged from 444.6 to 734.1. The mean posterior curvature from apex to periphery ranged from - 4.5 to - 9.1days preoperatively and from - 4.5 to - 9.2days at 12months. These were not statistically significant (ANOVA and unpaired T test). Our data suggest that CXL over an 8-mm zone can stabilize the peripheral cornea. Longer-term follow-up studies on the peripheral cornea after CXL will provide useful information.

Effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty.

To investigate the effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty (FBDALK). This is a retrospective analysis of patients who were diagnosed with advanced keratoconus between 2011 and 2014 in our hospital. The base of the cone in all patients did not exceed the central cornea at a 6-mm range. The FBDALK was performed by a same surgeon. All patients had a complete corneal suture removal and the follow-up records were intact. Patients who had graft-bed misalignment or who were complicated with a cataract or glaucoma were excluded. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and Pentacam examination data were recorded at two years postoperatively. The recorded data included the superior-inferior (S-I) and nasal-temporal (N-T) corneal thickness differences in 2, 4, 6, and 8 mm diameter concentric circles with the corneal apex as the center (S-I2 mm, S-I4 mm, S-I6 mm, S-I8 mm, N-T2 mm, N-T4 mm, N-T6 mm, and N-T8 mm), the linear, X-axis, and Y-axis distance between the corneal pupillary center and the cornea apex, total corneal astigmatism at a zone of 3 mm diameter from the corneal apex (TA3 mm), the astigmatic vector values J0 and J45, and the corneal total higher-order aberration for 3 and 6 mm pupil diameters (HOA3 mm and HOA6 mm). Statistical analysis was performed by SPSS 15.0. A total of 47 eyes of 46 patients met the criteria and were included in this study. The mean follow-up time was (28±7) months. The mean UCVA was 0.45±0.23 (logMAR) (MAR: minimum angle of resolution) and the mean BSCVA was 0.19±0.15 (logMAR), which were all significantly positively correlated with postoperative TA3 mm and HOA3 mm. The mean S-I corneal thickness differences were (44.62±37.74) μm, and the mean N-T was (38.57±32.29) μm. S-I2 mm was significantly positively correlated with J0 (r=0.31), J45 (r=0.42), HOA3 mm (r=0.37), and HOA6 mm (r=0.48). S-I4 mm and S-I8 mm were significantly positively correlated with HOA3 mm (r=0.30, r=0.40) and HOA6 mm (r=0.46, r=0.35). The X-axis distance between corneal pupillary center and corneal apex was significantly positively correlated with J45 (r=0.29). In patients with advanced keratoconus after FBDALK, the unevenly distributed thickness at corneal pupillary area and the misalignment of corneal apex and pupillary center might cause significant regular and irregular astigmatism, which affected the postoperative visual quality.

Cornea Full-field Displacement and Strain Measurement in Vivo Using Three-dimensional Digital Image Correlation.

Corneal biomechanics are becoming increasingly important for clinical evaluation and diagnosis, such as in refractive surgery, glaucoma, and keratoconus. We developed and used a new technique to measure the full-field displacement and strain of the cornea under elevated intraocular pressure in vivo. In this study, we propose a three-dimensional digital image correlation method for the determination of corneal biomechanical properties. Corneal deformation change on the rabbit eyeball was investigated under different inflation conditions with intraocular pressure levels of 2.3, 3.3, 5.3, and 6.9 kPa in vivo. The proposed method was able to measure the displacement of the corneal surface and to construct real-time full-field three-dimensional deformation vector fields and strain mapping. The results show that the strain distribution is not uniform on the corneal surface at each intraocular pressure level. Compression strains, rather than extensile strains, are dominant at the corneal apex region. This technique has the potential to be used as an assistive tool for the determination of corneal biomechanical properties in ophthalmologic investigations.

Assessment of the influence of viscoelasticity of cornea in animal ex vivo model using air-puff optical coherence tomography and corneal hysteresis.

Application of the air‐puff swept source optical coherence tomography (SS‐OCT) instrument to determine the influence of viscoelasticity on the relation between overall the air‐puff force and corneal apex displacement of porcine corneas ex vivo is demonstrated. Simultaneous recording of time‐evolution of the tissue displacement and air pulse stimulus allows obtaining valuable information related in part to the mechanical properties of the cornea. A novel approach based on quantitative analysis of the corneal hysteresis of OCT data is presented. The corneal response to the air pulse is assessed for different well‐controlled intraocular pressure (IOP) levels and for the progression of cross‐linking‐induced stiffness of the cornea. Micrometer resolution, fast acquisition and noncontact character of the air‐puff SS‐OCT measurements have potential to improve the in vivo assessment of mechanical properties of the human corneas.

Study of a high precision corneal curvature radius measurement system

In order to improve the measurement efficiency and measurement accuracy of corneal curvature, a high precision corneal curvature radius measurement system was designed. Based on the principle of film reflection imaging, the measurement light source (concentric circle with light-emitting diode lights) is projected onto the cornea of the human eye, and the human eye cornea with the measurement light source marker is imaged on the photodetector by an optical imaging objective lens and processed by the image processing. The height of the measurement light source on the photodetector to the center of the cornea is calculated. Finally, the method of least squares is used to find the corneal curvature radius. The system uses a double telecentric lens for the optical imaging objective lens to ensure that the optical system has a constant magnification in a certain depth of field. At the same time, low coherence interferometry technology is used to accurately measure the distance between the corneal apex and the measuring light source. The standard corneal simulated eye was tested with the designed prototype. The measurement accuracy was ±0.02 mm. The experimental results show that the high accuracy corneal curvature radius measurement system can effectively improve the accuracy of corneal curvature measurement.

Rotation asymmetry of the human sclera.

To characterize the mean topographical shape of the human sclera of a normal eye. Forty-five participants aged from 19 to 45years and with no previous ocular surgeries were included in this study. Four three-dimensional (3D) corneo-scleral maps from both eyes were acquired using a corneo-scleral topographer (Eye Surface Profiler). For each 3D map, the sclera (maximum diameter of 16mm) and cornea were automatically separated at the level of the limbus. The remaining 3D scleral ring was further fit to a quadratic function. The elevation difference between the original and fit data was calculated. For statistical analysis, sclera was divided into eight sectors: nasal, temporal, superior, inferior, supero-nasal, supero-temporal, inferior-nasal and inferior-temporal. In addition, sclera was separated as inner sclera (inner ring of 6-7-mm radius) and outer sclera (external ring of 7-8-mm radius). Horizontally, the nasal area of the sclera showed less elevation [mean (SD) -30 (52) μm (OD)] than the temporal area [mean (SD) 4 (47) μm (OD)], p<0.001. Vertically, the inferior area of the sclera [mean (SD) 32 (72) μm (OD)] was slightly less elevated than the superior area (mean (SD) 36 (84) μm, but this difference was not statistically significant (p=0.40). Besides, the asymmetry of the sclera was found to increase with radial distance from the corneal apex. No statistically significant difference was found between right and left eye. Human sclera is rotationally asymmetric, and its shape varies considerably between subjects.

Impact of a Displaced Corneal Apex in Small Incision Lenticule Extraction.

To evaluate the possible impact of a displaced corneal apex (point of maximum curvature) on visual results and tomographic parameters after small incision lenticule extraction (SMILE). In this retrospective evaluation, eyes with uncomplicated SMILE for myopia correction were classified in two groups based on their preoperative distance between the corneal apex and corneal vertex (corneal intercept with the patient's line of sight) of 1 mm or greater (large A-V distance) or less than 1 mm (small A-V distance). All surgeries were performed during the early learning curve of two surgeons. Visual outcome parameters included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refractive spherical equivalent (MRSE), and refractive astigmatism 3 months postoperatively. Scheimpflug-derived tomographic outcome parameters included mean keratometry value, root mean square higher order aberrations (RMS HOAs), and optical zone decentration. The study comprised 94 eyes of 48 patients: 44 eyes in the large A-V distance group and 50 eyes in the small A-V distance group. Preoperative and postoperative RMS HOAs were significantly higher in the large A-V distance group than in the small A-V distance group (P = .002 and .008, respectively). Postoperative CDVA was significantly better in the small A-V distance group (P = .014). There were no statistically significant differences in postoperative UDVA, MRSE, refractive astigmatism, mean keratometry value, and optical zone decentration. After SMILE, CDVA was significantly worse in eyes with a preoperatively displaced corneal apex compared to eyes with a more central corneal apex. However, good visual results were achieved in both groups. [J Refract Surg. 2018;34(7):460-465.].

Measurement of anterior segment parameters in Saudi adults with myopia

PurposeTo measure anterior segment parameters of the eye in myopic Saudi population using Pentacam. MethodThis is retrospective cross-sectional study. Subjects were divided into three groups: low, moderate and high myopia groups. Anterior segment parameters including: central corneal thickness (CCT), thinnest corneal thickness (TCT), apex corneal thickness (Apex CT), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV) and corneal astigmatism (CA) were measured by Pentacam. ResultsA total of 504 eyes of 252 Saudi subjects with myopia were included in this study. The mean age ± standard deviation (SD) of subjects was 28.73 ± 6.18 years. The mean CCT, TCT, Apex CT, CV, ACD, ACV and CA for all myopic subjects were 557.21 ± 29.36, 554.09 ± 29.28, 556.10 ± 37.06, 61.30 ± 3.23 μm, 3.31 ± 0.27 mm, 211.15 ± 34.22 mm3 and 0.89 ± 0.52 D, respectively. No significant differences (P > 0.05) were found between right and left eyes in all anterior segment parameters of all myopic eyes. However, a significant difference (P < 0.05) was found in ACD between low (3.27 ± 0.26 mm) and moderate (3.35 ± 0.30 mm) myopic groups. Within low myopia group, significant differences (P < 0.05) were found in ACD, ACV and CA between different genders. Anterior chamber depth and ACV values were lower in females while CA was lower in males. In addition, significant positive correlation was found between ACV and ACD in all myopic groups. ConclusionThis study provided valuable measurements of the anterior segments parameters of the eye in myopic Saudi population. These parameters could be useful for ophthalmic practitioners in the clinic.

Distribution of Anterior Chamber Parameters in Normal Chinese Children and the Associated Factors.

To describe the distribution of anterior chamber depth (ACD), anterior chamber volume (ACV), and anterior chamber angle (ACA) and establish the associated factors in the pediatric population in Shanghai, China. In this cross-sectional study, children aged 6 to 18 years from 9 primary and middle schools in Shanghai were enrolled. The Pentacam Scheimpflug camera was used to measure anterior eye chamber parameters. The distribution of ACD, ACV, ACA, and their associations with age, sex, body mass index, cycloplegic refractive error, axial length, intraocular pressure, and other parameters were analyzed. A total of 1321 children were included, with a mean age of 9.65±2.95 years. The mean ACA, ACD, and ACV values were 37.95±7.96 degrees, 3.22±0.23 mm and 194.89±28.95 mm, respectively, and were higher in boys than in girls. ACV and ACD had similar growth trend curves with age, whereas ACA was stable. Overall, 5% of the tested children had ACA values ≤24.91 degrees. Greater ACV, deeper ACD, shorter pupil diameter, shorter axial length, and thinner apex corneal thickness were the independent factors associated with wider ACA (R=13.0%, P<0.001). As one of diagnostic indicators of angle closure, ACA was stable with age. The results of this study should improve the current understanding of the distribution of anterior chamber parameters and the main factors affecting their variation.

Retraction notice to “The Globe’s Eccentric Rotational Axis: Why Medial Rectus Surgery is More Potent Than Lateral Rectus Surgery” (Ophthalmology. 2018;125:1234-1238)

Tablestypically recommend greater lateral rectus (LR) than medial rectus (MR) surgical doses for horizontal strabismus of any given magnitude, a difference unexplained by mechanical models that assume globe rotation about its center. We tested this assumption during horizontal ductions. Prospective observational study. Eighteen adult subjects with normal binocular vision. Surface coil magnetic resonance imaging at 390 or 430 μm resolution was obtained using 2-mm-thick contiguous axial planes while subjects fixated targets in central, right, and left gaze. Angular displacements of lines connecting the corneal apex through the minor lens axis to the retina were measured to approximate clinical ductions. Globe centers were calculated from their area centroids. Apparent lens and globe-optic nerve (ON) junction rotations around the globe center were then compared with clinical ductions. Apparent angular rotations of lenses and globe-ON junctions during horizontal ductions. Globe-ON junctions appeared to rotate significantly less around globe centers than did lenses for abduction (20.6°±4.7° vs. 27.4°±7.4°, ± standard deviation (SD), P < 0.001) and adduction (25.3°±6.7° vs. 31.9°±8.3°, P < 0.001). Both rotations differed significantly from clinical adduction (27.9°±8.3°, P < 0.007), but only in abduction was globe-ON junction rotation significantly less than clinical abduction (28.6°±9.4°, P < 0.001). The true geometric globe rotational center was 2.2±0.5 mm medial and 0.8±1.0 mm posterior to the geometric globe center and was displaced farther medially and posteriorly during adduction. This eccentricity imbues each millimeter of MR recession with approximately 30% more trigonometric rotational effect than equivalent LR recession. The medial and posterior eccentricities of the normal ocular rotational axis profoundly influence horizontal rectus action. The proximity of the globe's rotational axis to the MR shortens its lever arm relative to the LR, explaining why mechanical effects of smaller MR recessions are equivalent to larger LR recessions.

Ocular manifestation in Marfan syndrome: corneal biomechanical properties relate to increased systemic score points.

To evaluate corneal deformation to an air puff as a new noninvasive tool to document disease status in Marfan syndrome (MFS) METHODS: Prospective observational cohort study. We included patients diagnosed with MFS who had their routine cardiovascular follow-up and applied the revised Ghent nosology to define two subgroups according to a high (≥ 7) and a low (< 7 points) systemic score. Dynamic Scheimpflug-based biomechanical analyses (CorvisST® [CST; Oculus GmbH]) were performed. The main outcome measure was the displacement of the corneal apex as given by the parameters highest concavity (HC; in ms), peak distance (PD; in mm), and highest concavity deformation amplitude (DA; mm). Forty-three eyes of 43 individuals (19 female, 24 male; mean age 42.0 ± 12.0years, range 18-67years) diagnosed with MFS were included. Applying the Ghent criteria, 21 patients had an advanced systemic score of ≥ 7, and 22 had score points < 7. There were no differences in age or sex between both groups. In contrast, HC was faster (P = 0.004), and PD (P < 0.001) was longer in those individuals with systemic score ≥ 7; maximum DA did not result in a statistically significant difference between the groups (P = 0.250). In vivo noninvasive biomechanical analyses with CST offer a new, non-invasive method to identify pathologic corneal deformation responses in adults with MFS. In the future, corneal deformation to an air puff could thus assist early identification of patients with high Ghent score as an adjunct to existing diagnostic tests.

Scleral Shape and Its Correlations With Corneal Astigmatism.

To assess the correlation between the scleral shape and corneal astigmatism. Twenty-two participants (11 nonastigmatic and 11 astigmatic) aged from 19 to 36 years and with no previous ocular surgeries were included in this study. Three-dimensional (3D) corneoscleral maps from both eyes (44 eyes) were acquired using a corneoscleral topographer (Eye Surface Profiler). Each 3D map was split into 13 concentric annuli, each 0.5-mm wide, starting at 1.0-mm radius from the corneal apex to the scleral periphery at 7.5 mm from the apex. Each ring was fitted to a quadratic function of the radial distance to the apex, to calculate the elevation difference between the raw data and the fitting surface ring. For each ring, the resulting elevation difference between the original and fit data profile was fit to a sum of sine function. Decentration and astigmatic terms obtained from the sinusoidal fit were analyzed and compared between nonastigmatic and astigmatic groups. In astigmatic eyes, corneal and scleral asymmetry are highly correlated, but both appear independent of each other in nonastigmatic eyes. No significant difference between astigmatic and nonastigmatic eyes was found for the decentration term [P > 0.05/N (Bonferroni)], whereas for the astigmatic component, the differences were statistically significant [P < 0.05/N (Bonferroni)]. Corneal and scleral shapes are correlated in astigmatic eyes, which suggests that astigmatism is not restricted to the cornea but should rather be considered a property of the entire eye globe.

Effect of Conus Eccentricity on Visual Outcomes After Intracorneal Ring Segments Implantation in Keratoconus.

To investigate the potential impact of cone eccentricity on visual outcomes after Keraring (Mediphacos, Belo Horizonte, Brazil) implantation for keratoconus. Nineteen eyes from 19 patients with keratoconus who underwent femtosecond laser-assisted Keraring implantation for keratoconus were included in this retrospective study. Uncorrected visual acuity (UDVA), corrected visual acuity (CDVA), keratometric readings, central corneal thickness, maximum keratometric distance from corneal apex (DKmax), corneal thinnest point from corneal apex (DTh), and coma were evaluated preoperatively and 6 months after the Keraring implantation. DKmax and DTh were used as metrics reflecting the eccentricity of the cone. UDVA, CDVA, keratometric readings, and coma improved at 6 months postoperatively. However, there was no correlation between DKmax or DTh and visual outcomes at 6 months postoperatively. The data did not show any impact of the cone eccentricity on visual outcomes after Keraring implantation for keratoconus at 6 months postoperatively. [J Refract Surg. 2018;34(3):196-200.].

Changes in Corneal Curvature After Epiblepharon Surgery in Children.

We aimed to determine the change in corneal topography for 2-different corneal zones and 4-quadrants after epiblepharon correction in children. We retrospectively reviewed 39 patients (74 eyes) who underwent epiblepharon surgery. Keratometry measurements of corneal curvature were performed for 2 optical zones defined as circular areas with a radius of 3 and 5 mm from the corneal apex. Each optical zone was divided into quadrants (nasal, superior, temporal, and inferior). Keratometry readings for each quadrant of zone were compared between the preoperative and postoperative examinations (at 1, 3, and 6 months). The correlation between corneal astigmatism and curvature change was analyzed for each quadrant of the 3-mm optical zone. At 1 month postoperatively, the inferior and superior quadrants of the 3-mm optical zone became significantly flatter compared with the preoperative state, and this phenomenon became more pronounced at 3 months postoperatively (P < 0.05). However, no significant postoperative change in corneal curvature was noted for any quadrant of the 5-mm optical zone. There was a statistically significant correlation between the change in astigmatism and corneal curvature for the superior and inferior quadrants of the 3-mm optical zone (R = 0.394, P < 0.05; R = 0.460, P < 0.05; respectively). Astigmatism reduction was affected by corneal flatness in the inferior rather than the superior quadrant. Epiblepharon surgery results in reduction of corneal steepness at the vertical axis of the 3-mm optical zone, which correlates to astigmatism reduction.

Computed Tomography Measurements as a Standard of Exophthalmos? Two-Dimensional Versus Three-Dimensional Techniques

ABSTRACTPurpose: To compare measurements of exophthalmos using two-dimensional (2D) and three-dimensional (3D) computed tomography (CT) methods.Methods: The CT data of 50 patients with thyroid eye disease were collected. The exophthalmos measurements were performed using both 2D and 3D methods. The protrusion of the globe center, the deviation angle of the ocular axis, and the distance between the globe center and the corneal apex were also recorded. The agreements between Hertel exophthalmometry and different CT measurements were analyzed, and the geometrical relationship between the protrusion of the corneal apex and globe center were analyzed.Results: The measurement agreement from consecutive CT scans was significantly better using the 3D method than the 2D method (p < 0.05). The difference in exophthalmos measurements between the 2D and 3D methods was 0.9 ± 1.2 mm (p < 0.05), and the 3D exophthalmos measurement was more consistent with Hertel exophthalmometry. The exophthalmos of the corneal apex and the globe center agreed with the geometrical formula well. The location error between the corneal apexes marked on the 2D and 3D images was correlated with the vertical deviation angle of the ocular axis (r = 0.516).Conclusion: The reliability of CT measurements performed using a 3D method was better than those obtained using a conventional 2D method. The 3D measurements were also more consistent with the exophthalmometry results. The exophthalmos of the globe center might be considered an important reference for patients with severe strabismus.