Minimum Corneal Diameter and Anterior Steep Axis Curvature Share the Same Meridian: A Novel Finding.

PURPOSE: To define the external scleral sulcus (ESS) on a Scheimpflug image and use it for a morphometric analysis of corneal diameter (CD). DESIGN: Retrospective, cross-sectional study of pediatric Asian-Indian eyes. METHODS: One random eye of 353 subjects between 5 and 18 years underwent 25-scan Pentacam HR imaging. For all scans, densitometry values along the anterior corneal edge were recorded and differentiated. The peaks on the differentiated curve were chosen as the ESS points, and this distance between them was called CD. Vertical (vCD), maximum (maxCD), minimum (minCD) CD and their meridians were defined. Multiple regression models (MRMs) with CD and other Pentacam parameters were built to predict astigmatism and its axis, mean keratometry (Kmean), and Belin/Ambrósio enhanced ectasia display deviation (BAD-D). MRMs were validated using intraclass correlation coefficient (ICC). Estimated horizontal CD (hCD) was validated against digital caliper measurement using ICC. RESULTS: The ICC (95% CI) between caliper and hCD was 0.96 (0.93, 0.97). MRM predictions (P < .001) used CD parameters, anterior chamber depth, corneal volume and distance from the corneal thinnest location to apex. These predictions achieved an ICC of 0.34 (0.18, 0.46), 0.82 (0.78, 0.86), 0.87 (0.84, 0.89), and 0.81 (0.76, 0.84), respectively. The astigmatism axis prediction depended on the minCD and maxCD meridians. Its within-subject SD (4.97°) was less than 2 consecutive Pentacam scan angles (7.2°). CONCLUSIONS: The CD metric strongly correlated with the astigmatism axis, keratometry, and BAD-D. Its spatial description may be significant in corneal treatment planning and disease diagnoses.

Theranostic-guided corneal cross-linking: Preclinical evidence on a new treatment paradigm for keratoconus.

Theranostics is an emerging therapeutic paradigm of personalized medicine; the term refers to the simultaneous integration of therapy and diagnostics. In this work, theranostic-guided corneal cross-linking was performed on 10 human sclero-corneal tissues. The samples were soaked with 0.22% riboflavin formulation and underwent 9 minutes UV-A irradiance at 10 mW/cm2 using theranostic device, which provided both a measure of corneal riboflavin concentration and a theranostic score estimating treatment efficacy in real time. A three-element viscoelastic model was developed to fit the deformation response of the cornea to air-puff excitation of dynamic tonometry and to calculate the mean corneal stiffness parameter before and after treatment. Significant correlation was found between the theranostic score and the increase in mean corneal stiffness (R = 0.80; P < .001). Accuracy and precision of the theranostic score in predicting the induced corneal tissue stiffening were both 90%. The riboflavin concentration prior to starting the UV-A photo-therapy phase was the most important variable to allow corneal cross-linking to be effective. Theranostic UV-A light mediated imaging and therapy enables the operator to adopt a precise approach for achieving highly predictable biomechanical strengthening on individual corneas.

Assessing corneal cross-linking with reverberant 3D optical coherence elastography.

SIGNIFICANCE: Corneal cross-linking (CXL) is a well-known procedure for treating certain eye disorders such as keratoconus. However, characterization of the biomechanical changes in the cornea as a result of this procedure is still under active research. Specifically, there is a clinical need for high-resolution characterization of individual corneal layers. AIM: A high-resolution elastography method in conjunction with a custom optical coherence tomography system is used to track these biomechanical changes in individual corneal layers. Pre- and post-treatment analysis for both low-dose and high-dose CXL experiments are performed. APPROACH: A recently developed elastography technique that utilizes the theory of reverberant shear wave fields, with optical coherence tomography as the modality, is applied to pig corneas ex vivo to evaluate elasticity changes associated with corneal CXL. Sets of low-dose and high-dose CXL treatments are evaluated before and after treatments with three pairs of pig corneas per experiment. RESULTS: The reverberant three-dimensional (3D) optical coherence elastography (OCE) technique can identify increases in elasticity associated with both low-dose and high-dose CXL treatments. There is a notable graphical difference between low-dose and high-dose treatments. In addition, the technique is able to identify which layers of the cornea are potentially affected by the CXL procedure and provides insight into the nonlinearity of the elasticity changes. CONCLUSIONS: The reverberant 3D OCE technique can identify depth-resolved changes in elasticity of the cornea associated with CXL procedures. This method could be translated to assess and monitor CXL efficacy in various clinical settings.

Machine learning based strategy surpasses the traditional method for selecting the first trial Lens parameters for corneal refractive therapy in Chinese adolescents with myopia.

PURPOSE: Return zone depth (RZD) and landing zone angle (LZA) are important parameters of corneal refractive therapy (CRT) lenses. A new machine learning algorithm is proposed for prescribing CRT lens parameters in Chinese adolescents with myopia. METHODS: This is a retrospective study. In total, 1037 Chinese adolescents with myopia (1037 right eyes) were enrolled. A calculation model based on corneal elevation maps was constructed to calculate RZD and LZA for the four quadrants. Furthermore, multiple linear regression and optimized machine learning models were established to predict RZD and LZA values for different combinations of age, sex, and ocular parameters. The four methods (sliding card, linear regression, calculation and optimized machine learning) were then compared to the parameters of the final ordered lens. RESULTS: The optimized machine learning pipeline achieved the best performance. Age, sex, horizontal visible iris diameter (HVID), spherical equivalent refraction degree (SER), eccentricity (e), keratometric (K) readings, corneal astigmatism (CA), axial length (AL), AL/corneal curvature ratio (AL/MK), and anterior chamber depth (ACD) were significant to the machine learning model. The R values for the nasal, temporal, superior and inferior LZA based on machine learning were 0.843, 0.693, 0.866 and 0.762, respectively, and those for the RZD were 0.970, 0.964, 0.975 and 0.964, respectively. CONCLUSIONS: The feasibility and efficiency of an optimized machine learning method to predict LZA and RZD parameters has been demonstrated. The advantage of the proposed method is that it is more accurate, easier to use and faster to implement than the traditional sliding card method.

Iontophoresis-Assisted Rose Bengal and Green Light Corneal Cross-Linking.

PURPOSE: To evaluate the effects of the application of iontophoresis-assisted rose bengal and green light cross-linking (I-RGX) therapy on enucleated rabbit eyes for corneal biomechanical parameters, dye diffusion rates, and green light levels reaching deep tissues and to compare these parameters with a standard rose bengal and green light cross-linking (RGX) therapy. METHOD: Forty-five enucleated rabbit eyes were used in this study. To evaluate biomechanical changes, corneas were divided into the following 4 groups: the control group, the 0.1% rose bengal application group, the RGX group (100 J/cm), and the I-RGX group (100 J/cm). After this, corneal strips were evaluated with a uniaxial extensometer. To assess corneal dye diffusion, postprocedure dye depth was recorded with anterior segment optic coherence tomography. The amount of irradiation passing through the cornea during irradiation with 250 mW/cm irradiation power was measured with a laser power meter at the first, third, and seventh minutes. RESULTS: In the I-RGX-treated group especially, the mean elastic modulus and corneal stiffness values were about 4.7 times higher when compared with the controls and about 2.2 times higher than those in the RGX group. The rose bengal diffusion depth was 26.63% ± 3.84% of the total corneal thickness in the rose bengal drop group, but this value increased to 42.22% ± 4.77% in the iontophoresis group (<0.001). After iontophoresis, an average of 98% of the 100 J/cm green light was kept in the cornea. CONCLUSIONS: I-RGX is a very useful method for increasing corneal biomechanical strength and is highly effective in increasing the amount of corneal dye diffusion into the cornea while also minimalizing the amount of laser passage reaching deeper tissues.

Comparison of eye-rubbing effect in keratoconic eyes and healthy eyes using Scheimpflug analysis and a dynamic bidirectional applanation device.

PURPOSE: To compare the effect of eye rubbing on Scheimpflug imaging parameters and corneal biomechanics in eyes with keratoconus and healthy eyes. SETTING: Oftalmosalud Instituto de Ojos, Lima, Peru. DESIGN: Prospective cohort study. METHODS: The study included healthy and keratoconus patients who attended the institution between January 2017 and July 2017. Eye rubbing was performed for 1 minute followed by a 5-second break, followed by further rubbing for 1 minute. Baseline tests were performed before rubbing; post-rubbing tests were performed immediately after (0 minutes), and then again at 7 minutes and 14 minutes. Parameters related to anterior and posterior curvature and elevation, pachymetry, and corneal biomechanics obtained from tomography with a rotating Scheimpflug camera (Pentacam HR) and a dynamic bidirectional applanation device (Ocular Response Analyzer) were measured and compared between healthy and keratoconic eyes. RESULTS: The study included 30 healthy eyes and 31 keratoconic eyes. In the healthy group, the immediate mean changes in steeper anterior keratometry, posterior astigmatism, anterior chamber volume (ACV), flattest posterior keratometry, and Goldmann-correlated intraocular pressure (IOPg) after eye rubbing were 0.07 diopters (D) ± 0.15 (SD), -0.01 ± 0.08 D, 0.03 ± 7.06 mm3, -0.001 ± 0.04 mm, and -1.21 ± 1.99 mm Hg, respectively, whereas the mean changes in the keratoconus group were -0.03 ± 0.32 D, 0.14 ± 0.50 D, -5.09 ± 8.45 mm3, 0.03 ± 0.06 mm, and -1.61 ± 1.41 mm Hg, respectively. There were statistically significant differences between the preoperative and postoperative eye-rubbing values of posterior astigmatism, ACV, and IOPg in the keratoconus group (P = .03, P = .0003, and P = .001, respectively) but not in the healthy group (P = .65, P = .85, and P = .23, respectively). CONCLUSIONS: Unlike the healthy eyes group, the keratoconus group experienced significant changes in ACV, IOP, and corneal posterior astigmatism after eye rubbing.

Superior outcome of corneal collagen cross-linking using riboflavin with methylcellulose than riboflavin with dextran as the main supplement.

PURPOSE: To compare the effect of corneal collagen cross-linking (CXL) on progressive keratoconus using 0.1% riboflavin with either dextran or methylcellulose as the main supplement. METHODS: In a comparative case series, CXL was performed in 40 patients (40 eyes) using a riboflavin solution containing either dextran (dextran-riboflavin; n = 20) or methylcellulose (methylcellulose-riboflavin; n = 20). Changes in central corneal thickness (CCT), Scheimpflug tomography, maximal keratometry reading (Kmax ), visual acuity (VA) and endothelial cell density (ECD) were recorded. Stromal changes one month after surgery were analysed using optical coherence tomography (OCT) and in vivo confocal microscopy (IVCM). RESULTS: The CCT was significantly higher in the methylcellulose-riboflavin group during the CXL procedure. The IVCM demarcation line depth was 274 ± 80 (SD) µm in the dextran-riboflavin group and 442 ± 80 µm in the methylcellulose-riboflavin group (p < 0.001). Complete absence of keratocytes in the pre-endothelial stroma was found in none of the corneas treated with dextran-riboflavin and in 42% of the corneas treated with methylcellulose-riboflavin. Visibility of the OCT demarcation line was significantly lower in the methylcellulose-riboflavin group. Kmax and corrected distance visual acuity were improved in the methylcellulose-riboflavin group and stable in the dextran-riboflavin group after 2 years. Endothelial cell density (ECD) was stable in both groups. CONCLUSION: We found deeper structural changes in the methylcellulose-riboflavin group than in the dextran-riboflavin group. This may be explained by different riboflavin solution properties and raises safety concerns. The study also indicates improved effect using methylcellulose-riboflavin than dextran-riboflavin, possibly explained by deeper stromal CXL effect.

Polarization-sensitive optical coherence tomography imaging of the anterior mouse eye.

Polarization-sensitive optical coherence tomography (PS-OCT) enables noninvasive, high-resolution imaging of tissue polarization properties. In the anterior segments of human eyes, PS-OCT allows the visualization of birefringent and depolarizing structures. We present the use of PS-OCT for imaging the murine anterior eye. Using a spectral domain PS-OCT setup operating in the 840-nm regime, we performed in vivo volumetric imaging in anesthetized C57BL/6 mice. The polarization properties of murine anterior eye structures largely replicated those known from human PS-OCT imagery, suggesting that the mouse eye may also serve as a model system under polarization contrast. However, dissimilarities were found in the depolarizing structure of the iris which, as we confirmed in postmortem histological sections, were caused by anatomical differences between both species. In addition to the imaging of tissues in the anterior chamber and the iridocorneal angle, we demonstrate longitudinal PS-OCT imaging of the murine anterior segment during mydriasis as well as birefringence imaging of corneal pathology in an aged mouse.

COMPARISON OF CORNEAL WETTING PROPERTIES OF DIFFERENT DISPERSIVE OPHTHALMIC VISCOSURGICAL DEVICES: An Optical Coherence Tomography Study.

PURPOSE: To compare corneal wetting performances of different dispersive ophthalmic viscosurgical devices. METHODS: Three different types of dispersive ophthalmic viscosurgical devices, hydroxypropyl methylcellulose %2 (HPMC), sodium hyaluronate %3-sodium chondroitin sulphate %4 (HACS), and sodium hyaluronate %3 (HA), were applied on corneal surfaces of 10 healthy volunteer subjects repeatedly at 3 different time points. Corneal wetting properties of the ophthalmic viscosurgical devices were compared qualitatively and quantitatively by anterior segment optical coherence tomography for 30 minutes. RESULTS: Sodium hyaluronate 3% and HACS applications had a higher mean precorneal ophthalmic viscosurgical device thickness than HPMC application at all time points (seventh minute HPMC: 105.2 ± 25.3 µm, HA: 561.4 ± 115.8 µm, HACS: 481.2 ± 55 µm, P < 0.001). All HPMC applications were terminated by the 12th minute because of insufficient corneal wetting. Mean survival estimate time was significantly shortest for HPMC (11.5 ± 0.5 minutes, P < 0.001) and longest for HA (29.7 ± 0.28 minutes). It was slightly shorter for HACS (26.9 ± 0.87 minutes, P = 0.007) than the HA application. CONCLUSION: Sodium hyaluronate 3% and HACS provide superior corneal covering compared with HPMC with an effect that can be maintained up to 30 minutes. They may be an effective option for corneal wetting during long vitreoretinal surgeries with longer duration of effect and fever number of applications.

Optical coherence tomography of the Kayser-Fleischer ring: an ancillary diagnostic tool for Wilson's disease in children.

This report presents anterior segment optical coherence tomography (AS-OCT) images of Kayser-Fleischer ring (KFR) in a child. The AS-OCT images highlight differential reflectivity of the KFR depending on amount of copper deposited in cornea, thus supporting the role of AS-OCT as a follow-up tool. Utility of AS-OCT for diagnosing and documenting the KFR in children otherwise uncooperative for detailed slit lamp examination is discussed.

A study of central corneal thickness in glaucoma and nonglaucoma patients in a West African population.

PURPOSE: To compare central corneal thickness (CCT) in high-tension glaucomatous eyes and nonglaucomatous eyes with normal intraocular pressure (IOP) and to determine if there is any correlation between CCT and severity of glaucoma, as indicated by vertical cup-to-disc ratio. METHODS: A case-control study that involved 506 subjects at the Korle-Bu Teaching Hospital, Accra, Ghana, from August 2006 to July 2007. The cases were patients with (high tension and IOP more than 21 mm Hg) primary open-angle glaucoma, and the controls were patients with normal IOP (less than 21 mm Hg) and no evidence of glaucoma. The main outcome measures were CCT, as measured by ultrasonic pachymetry (model DGH 55 pachmate), and vertical cup-to-disc ratio. RESULTS: Five hundred six subjects were recruited: 253 cases (506 eyes) and 253 controls (505 eyes). The mean CCT of the right eye for the glaucoma cases was 524.28 µm [95% confidence interval (CI), 4.44; SD, 36.85] and for the controls was 530.00 µm (95% CI, 4.56; SD, 35.75). The mean CCT of the left eye for the glaucoma cases was 524.70 µm (95% CI, 4.48; SD, 36.20) and for the controls was 531.06 µm (95% CI, 4.40; SD, 35.52). The relation between CCT and cupping determined by Pearson correlation coefficient yielded values of -0.09 and 0.01 for the right and left eyes, respectively. CONCLUSION: There was no significant difference between mean CCT of cases and controls in the right eye (P = 0.08), but there was a weakly significant difference in the CCT of the left eye (P = 0.05). Also, there was no correlation between cup-to-disc ratio and CCT.

Influence of hyperbaric oxygen therapy on central corneal thickness.

BACKGROUND/AIMS: Hyperbaric oxygen (HBO) therapy is used in the treatment of several disorders. Little is known about the effects of HBO treatment on corneal thickness. The aim of this study was to investigate the effect of HBO treatment on central corneal thickness. METHODS: Thirty-two subjects (18 males and 14 females, mean age 57.3 ± 16.7 years) undergoing HBO treatment were consecutively enrolled. The subjects were assigned into diabetic (n = 16) and nondiabetic groups (n = 16). Best-corrected visual acuity was recorded before HBO treatment, and anterior and posterior segment examinations were performed on a slit lamp biomicrosope. Central corneal thickness was measured with an ultrasonic pachymeter before and immediately after HBO treatment, which lasted 120 min at 2.4 atmospheres absolute with three 30-min oxygen and two 5-min air breathing periods. RESULTS: HBO treatment did not change the central corneal thickness in diabetic subjects (547.6 ± 34.5 vs. 548.6 ± 34.6 µm; p = 0.606). In nondiabetic subjects, however, the central corneal thickness was significantly reduced after HBO treatment (576.5 ± 34.8 vs. 569.0 ± 34.8 µm; p < 0.001). CONCLUSION: A single exposure to HBO treatment reduced the central corneal thickness in nondiabetic subjects but not in diabetic subjects. However, the change in central corneal thickness was minor.

[Morphological features of corneal exposure to experimental near infrared emission laser].

Effect of laser radiation with wave length 1,4 microm on exposed cornea of isolated bull eye (in vitro) is studied. Experimental laser coagulator with wave length 1,4 microm based on the semiconductor laser with a fiber radiation output was used in the study. Cornea was exposed at the standardized distance to radiation with different energy settings. Coagulates were morphologically studied, photoregistration and morphometric analysis of obtained images were performed. The depth of radiation absorbtion, type and degree of corneal damage were estimated in the focus and marginal area. The analysis of results shows potential of this laser coagulator to be used for selective effects at different corneal layers. This laser may be applied both for coagulation and therapueutic purposes.

Modeling and percept of transcorneal electrical stimulation in humans.

Retinal activation via transcorneal electrical stimulation (TcES) in normal humans was investigated by comparing subject perception, model predictions, and brain activation patterns. The preferential location of retinal stimulation was predicted from 3-D admittance modeling. Visual cortex activation was measured using positron emission tomography (PET) and (18)F-fluorodeoxyglucose (FDG). Two different corneal electrodes were investigated: DTL-Plus and ERG-Jet. Modeling results predicted preferential stimulation of the peripheral, inferior, nasal retina during right eye TcES using DTL-Plus, but more extensive activation of peripheral, nasal hemiretina using ERG-Jet. The results from human FDG PET study using both corneal electrodes showed areas of visual cortex activation that consistently corresponded with the reported phosphene percept and modeling predictions. ERG-Jet was able to generate brighter phosphene percept than DTL-Plus and elicited retinotopically mapped primary visual cortex activation. This study demonstrates that admittance modeling and PET imaging consistently predict the perceived location of electrically elicited phosphenes produced during TcES.

Central corneal thickness and its relationship to intraocular pressure in mucopolysaccararidoses-1 following bone marrow transplantation.

PURPOSE: To examine the ocular findings in mucopolysaccaridoses-1 (MPS-1) and the relationship between intraocular pressure (IOP) and central corneal thickness following bone marrow transplantation. SETTING: clinical practice. SUBJECTS: 23 subjects with MPS-1 following bone marrow transplantation were examined. OBSERVATION PROCEDURES: age, sex, visual acuity, presence of strabismus, refractive error, fundus examination, intraocular pressure, and central corneal thickness were assessed for each individual. MAIN OUTCOME MEASURE: correlation of central corneal thickness with intraocular pressure. Only the right eye was used in correlations. RESULTS: Forty-six eyes of 23 subjects were examined. All subjects had been treated with successful bone marrow transplantation with mean follow-up of 8.5 years. Ages ranged from 17 months to 19 years (SD 5.03). Of the subjects, 60.8% were female; 85.5% were hyperopic; 8.6% had best-corrected visual acuity of >/=6/12; 34.5% had best-corrected visual acuity of <6/12 and >6/36 with 56.9% <6/36; 30% had strabismus. IOP ranged from 13 to 41 mm Hg with four children on antiglaucoma therapy. Central corneal thickness ranged from 484 microm to 705 microm and was moderately correlated with measured IOP in the right eye (r = 0.56). Corneal opacification moderately correlated with central corneal thickness (r = 0.57). Seventy percent had a normal disk evaluation; 30% had abnormal disk cupping. CONCLUSION: This is the first large case series of MPS-1 subjects demonstrating a correlation between measured IOP and central corneal thickness. All subjects had corneal opacification moderately correlating with corneal pachymetry.

Potato gun ocular injury.

PURPOSE: This study aimed to identify a dangerous new weapon capable of causing damage to the ocular and periocular regions. METHODS: The authors report two patients who had penetrating ocular injury in the past year because of homemade recreational potato guns. RESULTS: In one 14-year-old boy, projectiles from the firing of a potato gun resulted in orbital and cranial injuries that were life threatening with widespread fractures, marked disruption of facial structures, a cerebrospinal fluid fistula requiring bifrontal surgical repair, and loss of one eye. In a separate accident with a different potato gun, a 14-year-old boy who was wearing glasses at the time of injury had a sight-threatening perforating corneal laceration. CONCLUSION: Practitioners must be aware of the existence of these new, homemade unregulated devices. Information about the use and construction of these guns is widespread on the Internet, but no injuries resulting from these guns currently are documented in the medical literature.

Assessment of diagnostic criteria in management of infantile glaucoma. An analysis of tonometry, optic disc cup, corneal diameter and axial length.

BACKGROUND: Infantile glaucoma is characterized by increased intraocular pressure, enlarged corneal diameters, optic disc cupping and typical anamnesis. The aim of our study was to evaluate the validity of diagnostic criteria in differentiating between manifest infantile glaucoma and glaucoma-suspected eyes (e.g. megalocornea). METHODS: We retrospectively analyzed consecutive charts of 87 children undergoing ophthalmic examination under general anesthesia because of manifest or suspected glaucoma. At first examination in our clinic age-related differences of diagnostic parameters between 52 children with infantile glaucoma requiring glaucoma-surgery (group A) and 35 glaucoma-suspect children requiring no surgery (group B) were assessed using non-parametric Mann-Whitney U Test. Influence of tonometry, optic disc cupping, and changes of axial length and corneal diameter during the follow-up on our decision for surgery were also investigated. RESULTS: Tonometry, axial length of the eye, optic disc cupping, incidence of corneal opacities and age of onset of symptoms were significantly different in the two groups (p < or = 0.002) from first through third year of life, whereas corneal diameters were not significantly different in the second and third year of life. Advanced disc excavation (C/D > 0.6) and increased IOP (> 16 mmHg) were significantly associated with the decision to undertake subsequent surgery (p < 0.0001). Changes of corneal diameter and axial length during follow-up showed no significant difference between those glaucoma patients who needed re-operation and those who did not, after the first year of life. CONCLUSION: Corneal diameters and axial length were helpful in the diagnosis of infantile glaucoma, but of limited use in the follow-up. The decision to undertake surgery was based upon tonometry and optic disc evaluation.