Study of Morpho-Geometric Variables to Improve the Diagnosis in Keratoconus with Mild Visual Limitation

The extraction and application of antisymmetric characteristics of the cornea during air-puff perturbations

BACKGROUND

A non-contact tonometer is used to measure intraocular pressure, and studies have primarily relied on apex displacements to assess corneal properties. However, previous studies have overlooked the asymmetric characteristics of lateral corneal perturbations, leading to a gap in understanding of the lateral mechanical properties and its application.

METHOD

To investigate these lateral perturbations, we designed an experiment to sequentially record the corneal profiles when two consecutive air-puffs were applied at the center of the same cornea within a short period. Moreover, we used modal decomposition to decompose anterior surface profiles into symmetric and antisymmetric modes to comprehensively analyze the asymmetric characteristics. To extract mechanical properties, we utilized high-pass frequency analysis (>250 Hz) to filter out noise and errors.

RESULTS

Symmetric modes between the two consecutive air-puffs exhibited major similarities during vibration; however, antisymmetric modes exhibited minor differences in lateral perturbations of asymmetric vibration. The antisymmetric modes might be related to air-puff misalignment and mechanical properties. Through applying frequency analysis, the mechanical properties could be proven at high frequencies and misalignment shown at low frequencies. Furthermore, we compared the corneal vibration profiles of 259 healthy participants and 50 patients with keratoconus. Their properties showed that the antisymmetric modes of the keratoconus group exhibited a completely opposite direction of deformation compared to that in the healthy group.

CONCLUSIONS

Our proposed algorithm not only extracts antisymmetric characteristics but also offers valuable insights into decompose misalignment and mechanical properties of healthy and keratoconus corneas, presenting a new perspective for corneal biomechanics.

Subclinical keratoconus detection with three-dimensional (3-D) morphogeometric and volumetric analysis

PURPOSE

To assess the efficacy of morphogeometric and volumetric characterization of the cornea based on three-dimensional (3-D) modelling in diagnosis of subclinical keratoconus (KC).

METHODS

Cross-sectional study. Ninety-three eyes with subclinical KC with a best spectacle-corrected distance visual acuity ≥20/20 (grade zero KC according to the RETICS classification) and 109 control eyes were included. Computer-based 3-D corneal morphogeometric model was generated using raw topographic data. Distance-, area- and volume-based parameters were used for statistical analysis. Distance parameters included deviation of anterior (D_apexant )/posterior (D_apexpost ) apices and minimum thickness points (D_mctant , D_mctpost ) from corneal vertex, and D_apexant -D_apexpost difference. Areal variables were derived from anterior (A_ant ) and posterior (A_post ) corneal surfaces, sagittal plane passing through corneal apices (A_apexant , A_apexpost ) and thinnest point (A_mctant , A_mctpost ). Total corneal volume (V_total ) and volumetric distribution (with 0.1mm steps) centred to thinnest corneal point (VOL_mct ) and anterior (VOL_aap )/posterior (VOL_pap ) apices comprised the volume-based parameters.

RESULTS

In the subclinical KC group, all D values, D_apexant -D_apexpost difference, A_ant , A_post and A_apexant values were higher (p < 0.001), while A_apexpost , A_mctpost , V_total , VOL_mct , VOL_aap and VOL_pap values were lower when compared to the control group (p < 0.001). Regression analysis-based formula correctly classified 96.8% of the eyes with subclinical KC and 94.5% of the normal ones (p < 0.0001).

CONCLUSIONS

Eyes with subclinical KC seem to represent asymmetrically displaced anterior and posterior corneal apex, corneal thinning and volume loss. 3-D morphogeometric and volumetric parameters and differentiation formula can be incorporated into topography software to detect subclinical KC with high sensitivity and specificity in clinical practice.

An innovative approach for determining the customized refractive index of ectatic corneas in cataractous patients

The aim of this study is to determine the customized refractive index of ectatic corneas and also propose a method for determining the corneal and IOL power in these eyes. Seven eyes with moderate and severe corneal ectatic disorders, which had been under cataract surgery, were included. At least three months after cataract surgery, axial length, cornea, IOL thickness and the distance between IOL from cornea, and aberrometry were measured. All the measured points of the posterior and anterior parts of the cornea converted to points cloud and surface by using the MATLAB and Solidworks software. The implanted IOLs were designed by Zemax software. The ray tracing analysis was performed on the customized eye models, and the corneal refractive index was determined by minimizing the difference between the measured aberrations from the device and resulted aberrations from the simulation. Then, by the use of preoperative corneal images, corneal power was calculated by considering the anterior and posterior parts of the cornea and refractive index of 1.376 and the customized corneal refractive index in different regions and finally it was entered into the IOL power calculation formulas. The corneal power in the 4 mm region and the Barrett formula resulted the prediction error of six eyes within ± 1 diopter. It seems that using the total corneal power along with the Barrett formula can prevent postoperative hyperopic shift, especially in eyes with advanced ectatic disorders.

Quantitative Assessment of Ophthalmic Viscosurgical Devices on Visibility, Spreadability, and Durability as Corneal Wetting Agents for the Wet Shell Technique

Purpose

To evaluate ophthalmic viscosurgical devices (OVDs) as corneal wetting agents for the wet shell technique, a common procedure in Japan to maintain the wettability of corneal surfaces.

Methods

We surveyed Japanese ophthalmologists to determine the current state of the wet shell technique. After developing three ex vivo testing methods, we evaluated the corneal wetting properties of OVDs including 3% hyaluronic acid (HA) solution and OVD products, Opegan, Opelead, Viscoat, Shellgan, Discovisc, and Opegan-Hi.

Results

Overall, 214 ophthalmologists (70%) had performed the wet shell technique, and 91% of ophthalmologists who performed vitreous surgery had performed this technique. Using a questionnaire, we evaluated the performance of OVD as corneal wetting agents as follows: (i) visibility, smoothness of OVD surface; (ii) spreadability, coverage of the cornea; and (iii) retention durability, residual ratio of OVD on the corneal surface. The smoothness and spreadability of Opegan, Opelead, and 3% HA were superior to other OVDs. Adding an appropriate amount of balanced salt solution to the other OVDs improved smoothness and spreadability similar to that of Opelead or 3% HA. Shellgan and Viscoat, combination OVDs consisting of 3% HA and 4% chondroitin sulfate, showed high retention durability, resulting in remaining longer on the cornea compared with other OVDs.

Conclusions

Physical properties of OVDs tested in this study may provide useful information for ophthalmologists to select a suitable OVD when performing the wet shell technique.

A Machine-Learning Model Based on Morphogeometric Parameters for RETICS Disease Classification and GUI Development

This work pursues two objectives: defining a new concept of risk probability associated with suffering early-stage keratoconus, classifying disease severity according to the RETICS (Thematic Network for Co-Operative Research in Health) scale. It recruited 169 individuals, 62 healthy and 107 keratoconus diseased, grouped according to the RETICS classification: 44 grade I; 18 grade II; 15 grade III; 15 grade IV; 15 grade V. Different demographic, optical, pachymetric and eometrical parameters were measured. The collected data were used for training two machine-learning models: a multivariate logistic regression model for early keratoconus detection and an ordinal logistic regression model for RETICS grade assessments. The early keratoconus detection model showed very good sensitivity, specificity and area under ROC curve, with around 95% for training and 85% for validation. The variables that made the most significant contributions were gender, coma-like, central thickness, high-order aberrations and temporal thickness. The RETICS grade assessment also showed high-performance figures, albeit lower, with a global accuracy of 0.698 and a 95% confidence interval of 0.623–0.766. The most significant variables were CDVA, central thickness and temporal thickness. The developed web application allows the fast, objective and quantitative assessment of keratoconus in early diagnosis and RETICS grading terms.

Paediatric Orthopaedic Surgery with 3D Printing: Improvements and Cost Reduction

This paper presents a a novel alghorithm of diagnosis and treatment of rigid flatfoot due to tarsal coalition. It introduces a workflow based on 3D printed models, that ensures more efficiency, not only by reducing costs and time, but also by improving procedures in the preoperative clinical phase. Since this paper concerns the development of a new methodology that integrates both engineering and medical fields, it highlights symmetry. An economic comparison is made between the traditional method and the innovative one; the results demonstrate a reduction in costs with the latter. The current, traditional method faces critical issues in diagnosing the pathologies of a limb (such as the foot) and taking decisions for further treatment of the same limb. The proposed alternative methodology thus uses new technologies that are part of the traditional workflow, only replacing the most obsolete ones. In fact, it is increasingly becoming necessary to introduce new technologies in orthopedics, as in other areas of medicine, to offer improved healthcare services for patients. Similar clinical treatments can be performed using the aforementioned technologies, offering greater effectiveness, more simplicity of approach, shorter times, and lower costs. An important technology that fits into this proposed methodology is 3D printing.

Assessment of the Association between In Vivo Corneal Morphogeometrical Changes and Keratoconus Eyes with Severe Visual Limitation

Assessing changes suffered by the cornea as keratoconus progresses has proven to be vital for this disease diagnosis and treatment. This study determines the corneal biometric profile in eyes considered as affected by keratoconus (KC) showing severe visual limitation, by means of in vivo 3D modelling techniques. This observational case series study evaluated new objective indices in 50 healthy and 30 KC corneas, following a validated protocol created by our research group, which has been previously used for diagnosis and characterization of KC in asymptomatic (preclinical) and mild visually impaired eyes. Results show a statistically significant reduction of corneal volume and an increase of total corneal area in the severe KC group, being anterior and posterior corneal surfaces minimum thickness points the best correlated parameters, although with no discrimination between groups. Receiving operator curves were used to determine sensitivity and specificity of selected indices, being anterior and posterior apex deviations the ones which reached the highest area under the curve, both with very high sensitivity (96.7% and 90%, respectively) and specificity (94.0% and 99.9%, respectively). The results suggest that once severe visual loss appears, anterior corneal topography should be considered for a more accurate diagnosis of clinical KC, being anterior apex deviation the key metric discriminant. This study can be a useful tool for KC classification, helping doctors in diagnosing severe cases of the disease, and can help to characterize corneal changes that appear when severe KC is developed and how they relate with vision deterioration.

Innovative Methodology of On-Line Point Cloud Data Compression for Free-Form Surface Scanning Measurement

In order to obtain a highly accurate profile of a measured three-dimensional (3D) free-form surface, a scanning measuring device has to produce extremely dense point cloud data with a great sampling rate. Bottlenecks are created owing to inefficiencies in manipulating, storing and transferring these data, and parametric modelling from them is quite time-consuming work. In order to effectively compress the dense point cloud data obtained from a 3D free-form surface during the real-time scanning measuring process, this paper presents an innovative methodology of an on-line point cloud data compression algorithm for 3D free-form surface scanning measurement. It has the ability to identify and eliminate data redundancy caused by geometric feature similarity between adjacent scanning layers. At first, the new algorithm adopts the bi-Akima method to compress the initial point cloud data; next, the data redundancy existing in the compressed point cloud is further identified and eliminated; then, we can get the final compressed point cloud data. Finally, the experiment is conducted, and the results demonstrate that the proposed algorithm is capable of obtaining high-quality data compression results with higher data compression ratios than other existing on-line point cloud data compression/reduction methods.