Analysis of Treatment Discontinuation in Orthokeratology: Studying Efficacy, Safety, and Patient Adherence Over Six Months.

PURPOSE: This study aimed to evaluate the efficacy, safety, and participant compliance of orthokeratology treatment for the correction of myopic refractive errors over a six-month prospective study and to define the potential reasons for early treatment discontinuation. METHODS: A total of 32 participants with low-to-moderate myopia were fitted with the spherical model of corneal refractive therapy (CRT) orthokeratology lenses (Paragon Vision Sciences) and followed over six months, with specific attention to alterations in refractive error, corneal topography, and epithelial thickness. Concurrently, participant feedback and reasons for any treatment discontinuation were documented. RESULTS: Significant changes in refractive error and in corneal topography were observed, with approximately 50% of the refractive error being corrected on the first night of use and 100% by the first two weeks (P<0.001). Central epithelial thickness experienced substantial thinning, reducing to 15.65±4.49 µm (67.38%) (P<0.001) after 6 months of lens use. Six participants withdrew from this study for varied reasons, including unmet visual expectations and difficulty adhering to the lens-wearing regimen. Notably, the dropout group exhibited higher baseline low-order aberrations and less prolate corneas than those who persisted with the treatment (P<0.05). CONCLUSION: Orthokeratology with CRT is efficacious and safe for the correction of low-to-moderate myopia in adults, but a portion of patients discontinue the treatment in the first 6 months of contact lens wear. Special care should be taken when recommending orthokeratology in patients with higher levels of myopia and corneas with less prolate shape, providing more realistic expectations and even changing to dual axis or more sophisticated designs.

Establishing Standardization Guidelines For Finite-Element Optomechanical Simulations of Refractive Laser Surgeries: An Application to Photorefractive Keratectomy.

Purpose: Computational models can help clinicians plan surgeries by accounting for factors such as mechanical imbalances or testing different surgical techniques beforehand. Different levels of modeling complexity are found in the literature, and it is still not clear what aspects should be included to obtain accurate results in finite-element (FE) corneal models. This work presents a methodology to narrow down minimal requirements of modeling features to report clinical data for a refractive intervention such as PRK. Methods: A pipeline to create FE models of a refractive surgery is presented: It tests different geometries, boundary conditions, loading, and mesh size on the optomechanical simulation output. The mechanical model for the corneal tissue accounts for the collagen fiber distribution in human corneas. Both mechanical and optical outcome are analyzed for the different models. Finally, the methodology is applied to five patient-specific models to ensure accuracy. Results: To simulate the postsurgical corneal optomechanics, our results suggest that the most precise outcome is obtained with patient-specific models with a 100 µm mesh size, sliding boundary condition at the limbus, and intraocular pressure enforced as a distributed load. Conclusions: A methodology for laser surgery simulation has been developed that is able to reproduce the optical target of the laser intervention while also analyzing the mechanical outcome. Translational Relevance: The lack of standardization in modeling refractive interventions leads to different simulation strategies, making difficult to compare them against other publications. This work establishes the standardization guidelines to be followed when performing optomechanical simulations of refractive interventions.

Modeling and Prediction of the Immediate and Short-Term Effect of Myopic Orthokeratology.

PURPOSE: To characterize the clinical changes occurring in the initial phase of the orthokeratology (OK) treatment for myopia correction, developing a model of prediction of the refractive changes in such phase. METHODS: Prospective study enrolling 64 eyes of 32 patients (range, 20-40 years) undergoing myopic OK treatment with the reverse geometry contact lens CRT (Paragon Vision Science). Changes in uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), refraction, corneal topography, ocular aberrations, and corneal epithelial thickness were evaluated during the first hour of OK lens wear and after 1 week of OK treatment. Multiple linear regression analysis was used to obtain a model to predict the short-term refractive effect of OK. RESULTS: The UCVA improved at each visit, reaching normal visual acuity values after a week (P<0.001) of OK treatment, which was consistent with the significant spherical equivalent (SE) reduction and central flattening (P<0.001). Multiple linear regression analysis revealed that one night change in refraction (ΔR×1N) could be predicted according to the following expression (P<0.001, R2=0.686): ΔR×1N=1.042+0.028×Age+1.014×BCET (baseline central epithelium thickness)-0.752×BKm (baseline mean keratometry)-1.405×BSE (baseline SE)+1.032×ΔR×1 h (change in SE after 1 hr of OK lens use). Similarly, a statistically relevant linear relationship was obtained for predicting the refractive change after 1 week (ΔR×1W) of OK use (P<0.001, R2=0.928): ΔR×1W=3.470-1.046×BSE-1.552×BBCVA (baseline BCVA)-0.391×BKm+0.450×ΔR×1 h. CONCLUSIONS: The immediate and short-term refractive effects of myopic OK with the reverse geometry contact lens CRT can be predicted with enough accuracy from baseline and first trial visits data.

Corneal Biomechanics After Intrastromal Ring Surgery: Optomechanical In Silico Assessment.

Purpose: To provide a biomechanical framework to better understand the postsurgical optomechanical behavior of the cornea after ring implantation. Methods: Calibrated in silico models were used to determine the corneal shape and stresses after ring implantation. After mechanical simulations, geometric ray-tracing was used to determine the change in spherical equivalent. The effect of the surgical procedure, circadian variation of intraocular pressure, or the biomechanical weakening introduced by keratoconus (KC) were evaluated for each intrastromal ring. Results: Models predicted the postsurgical optomechanical response of the cornea at a population level. The localized mechanical effect of the additional intrastromal volume introduced by the implants (size and diameter) drives the postsurgical corneal response. However, central corneal stresses did not increase more than 50%, and thus implants did not strengthen the cornea globally. Because of the biomechanical weakening introduced by laser pocketing, continuous implants in a pocket resulted in higher refractive corrections and in the relaxation of the anterior stroma, which could slow down KC progression. Implants can move within the stroma, acting as a dynamic pivot point that modifies corneal kinematics and flattens the corneal center. Changes in stromal mechanical properties did not impact on refraction for normal or pathological corneas. Conclusions: Implants do not stiffen the cornea but create a local bulkening effect that regularizes the corneal shape by modifying corneal kinematics without canceling corneal motion. Translational Relevance: In silico models can help to understand corneal biomechanics, to plan patient-specific interventions, or to create biomechanically driven nomograms.

Geometrical characterization of the corneo-scleral transition in normal patients with Fourier domain optical coherence tomography.

PURPOSE: To characterize the geometry at the corneo-scleral transition for a normal population and its correlation with other anatomic parameters of the eyeball. METHODS: Transversal epidemiologic study on a sample of 100 individuals (right eye) in different ethnic groups (Africans and Caucasians). All of them were examined with Fourier domain optical coherence tomography, auto-refractometer, topographer, and biometer to obtain the corneo-scleral angle (CSA) and additional clinical parameters. The dataset was analyzed to determine correlations between different anatomical parameters and nasal (CSAn) and temporal CSA (CSAt) values. RESULTS: The CSAt presents a significant but low correlation with the anterior chamber depth-ACD (r = 0.25; p = 0.024), the white-to-white (W-W) distance (r = 0.27; p = 0.022), and the anterior chamber volume (r = 0.25; p = 0.016). CSAn did not correlate significantly with any clinical variable, with all values being lower than 179° (concave). Ethic groups presented significant differences for pachymetry (Pac) and corneal volume (p = 0.033 and p = 0.014), being greater for Caucasians, and temporal corneo-iridial angle (p = 0.006), being greater for Africans. CSA presented and inverse correlation with age. CONCLUSIONS: The CSAn presents a more concave profile for the normal population, whereas the CSAt presents a planar-convex profile with a great influence of age. In particular, the older the patient, the more convex the CSAt is. This age-related evolution of the CSAt and the concavity on the nasal direction must be considered when prescribing scleral contact lenses or when performing limbal incisions during refractive interventions.

Differences in corneo-scleral topographic profile between healthy and keratoconus corneas.

PURPOSE: To evaluate the differences in corneo-scleral topographic profile between healthy and keratoconus eyes, and their potential diagnostic ability for keratoconus detection. METHODS: Prospective comparative study including 21 keratoconic eyes (11 patients) and 88 healthy eyes (88 patients). In all cases, a complete eye exam was performed including an evaluation of the corneo-scleral profile. The diagnostic ability of corneo-scleral topographic parameters to detect keratoconus was evaluated using the receiver operating characteristic (ROC) curve. RESULTS: A significant lower inferior tangent angle at limbus (ITA) was found in the keratoconic group compared to the control group (p = 0.024). Regarding sagittal heights, significant differences between groups were found in temporal sagittal height (TSH) for 11 mm (p = 0.040), 12 mm (p = 0.041) and 13 mm corneal chords (p = 0.040), difference between temporal and nasal sagittal heights (T-NSH) for 12 mm (p = 0.025) and 13 mm (p = 0.034), and maximum sagittal height (MaxSH) for 12 mm (p = 0.043), with higher values in keratoconus. In bilateral cases, these differences were not found when comparing with the least severe keratoconus eye. Statistical significance for the ROC curve was only found for ITA (p = 0.025), 12-mm (p = 0.048) and 13-mm TSH (p = 0.042), and 13-mm T-NSH (p = 0.037), with cutoff values associated to limited values of sensitivity and specificity. CONCLUSIONS: The corneo-scleral profile in keratoconus presents higher levels of asymmetry compared to healthy eyes, especially in eyes with moderate and advanced stages of the disease. The diagnostic accuracy of corneo-scleral topographic data alone for keratoconus detection is limited and must be used in conjunction with other clinical parameters.

Characterization of Corneoscleral Geometry Using Fourier Transform Profilometry in the Healthy Eye.

OBJECTIVE: To characterize peculiarities of the corneoscleral geometry in healthy eyes. METHODS: This is a prospective case series including 88 healthy eyes of 88 patients with an age ranging from 21 to 73 years. A complete ocular examination was performed with emphasis on the analysis of the corneoscleral topographic profile with the Fourier transform profilometer Eye Surface Profiler (Eaglet-Eye BV, Houten, the Netherlands). The distribution of different topographic parameters was evaluated, as well as the correlations between corneal and scleroconjunctival parameters. RESULTS: Mean values of 8.64±0.37 (range, 7.81-9.50 mm), 6.06±0.52 (4.88-7.63 mm) and 11.93±1.32 mm (8.17-15.89 mm) were obtained for inner, limbal, and outer best-fit sphere, respectively. Mean values of 8.54±0.38 (7.86-9.66 mm) and 13.35±1.29 mm (11.05-17.31 mm) were obtained for mean corneal and scleral radius, respectively. Regarding tangent angles at limbus, mean values of 35.31±6.55°, 38.76±5.90°, 32.75±7.04°, and 25.91±8.99° were obtained for nasal, temporal, superior, and inferior angles, respectively. Mean difference between temporal and nasal sagittal heights increased from -1.48±120.70 µm for a chord of 11 mm to 73.53±236.55 µm for a chord of 14 mm. A weak but statistically significant correlation was found between corneal and scleral radii (r=0.325, P=0.004). The maximum sagittal height for a diameter of 12 mm was significantly correlated with flattest keratometry, astigmatism, corneal diameter, and corneal eccentricity (R: 0.77, P<0.001). CONCLUSIONS: The scleroconjunctival surface in the healthy eye presents some level of nasotemporal asymmetry that is higher with increasing diameters of analysis.

Template-based methodology for the simulation of intracorneal segment ring implantation in human corneas.

Keratoconus is an idiopathic, non-inflammatory and degenerative corneal disease characterised by a loss of the organisation in the corneal collagen fibrils. As a result, keratoconic corneas present a localised thinning and conical protrusion with irregular astigmatism and high myopia that worsen visual acuity. Intracorneal ring segments (ICRSs) are used in clinic to regularise the corneal surface and to prevent the disease from progressing. Unfortunately, the post-surgical effect of the ICRS is not explicitly accounted beforehand. Traditional treatments rely on population-based nomograms and the experience of the surgeon. In this vein, in silico models could be a clinical aid tool for clinicians to plan the intervention, or to test the post-surgical impact of different clinical scenarios. A semi-automatic computational methodology is presented in order to simulate the ICRS surgical operation and to predict the post-surgical optical outcomes. For the sake of simplicity, circular cross section rings, average corneas and an isotropic hyperelastic material are used. To determine whether the model behaves physiologically and to carry out a sensitivity analysis, a [Formula: see text] full-factorial analysis is carried out. In particular, how the stromal depth insertion, horizontal distance of ring insertion (hDRI) and diameter of the ring's cross section ([Formula: see text]) are impacting in the spherical and cylindrical power of the cornea is analysed. Afterwards, the kinematics, mechanics and optics of keratoconic corneas after the ICRS insertion are analysed. Based on the parametric study, we can conclude that our model follows clinical trends previously reported. In particular and although there is an improvement in defocus, all corneas presented a change in their optical aberrations. The stromal depth insertion is the parameter that affects the corneal optics the most, whereas hDRI and [Formula: see text] are less important. Not only that, but it is almost impossible to achieve an optimal trade-off between spherical and cylindrical correction. Regarding the mechanical behaviour, inserting the rings at 65% depth or above will cause the cornea to slightly bend. This abnormal stress distribution greatly distorts the corneal optics and, more importantly, could be the cause of clinical problems such as corneal extrusion. Not only that, but our model also supports that rings are acting as restraint elements which relax the stresses of the corneal stroma in the cone of the disease. However, depending on the exact spatial location of the keratoconus, the insertion of rings could promote its evolution instead of preventing it. ICRS inserted deeper will prevent keratoconus in the posterior stroma from growing (relaxation of posterior surface), but will promote its growing if they are located in the anterior surface (increment of stress). In conclusion, the methodology proposed is suitable for simulating long-term mechanical and optical effects of ICRS insertion.