Central and peripheral scleral lens-induced corneal oedema.

PURPOSE: To quantify the magnitude of central and peripheral scleral lens-induced corneal oedema for a range of fluid reservoir thicknesses, and to compare these experimental results with theoretical models of corneal oedema both with and without limbal metabolic support (i.e., the lateral transport of metabolites and the influence of the limbal vasculature). METHODS: Ten young healthy participants wore scleral lenses (KATT™, Capricornia Contact Lenses) fitted with low (mean 141 µm), medium (482 µm) and high (718 µm) central fluid reservoir thickness values across three separate study visits. The scleral lens thickness, fluid reservoir thickness and stromal corneal oedema were measured using optical coherence tomography. Oedema was quantified across the central (0-2.5 mm from the corneal apex) and peripheral (1.25-3 mm from the scleral spur) cornea. Experimental data were compared with published theoretical models of central to peripheral corneal oedema. RESULTS: Stromal oedema varied with fluid reservoir thickness (p < 0.001) for both central and peripheral regions. The mean (standard deviation) stromal oedema was greater for the medium (2.08 (1.21)%) and high (2.22 (1.31)%) fluid reservoir thickness conditions compared to the low condition (1.00 (1.01)%) (p ≤ 0.01). Stromal oedema gradually increased from the corneal centre to the periphery by ~0.3% on average (relative increase of 18%), but the change did not reach statistical significance. This trend of increasing, rather than decreasing, oedema towards the limbus is consistent with theoretical modelling of peripheral oedema without metabolic support from the limbus. CONCLUSIONS: The central and peripheral cornea displayed a similar magnitude of oedema, with increasing levels observed for medium and high fluid reservoir thicknesses. The gradual increase in oedema towards the limbus is consistent with a 'without limbal metabolic support' theoretical model.

Corneal oedema during open-eye fenestrated scleral lens wear.

INTRODUCTION: Studies examining the effect of fenestrating soft and corneal rigid contact lenses upon corneal oedema have yielded conflicting results. Although often utilised in clinical practice, no studies have quantified the effect of fenestrating a scleral contact lens upon corneal oedema. Therefore, the aim of this experiment was to examine the effect of incorporating a single peripheral fenestration on central corneal oedema during short-term open-eye scleral lens wear, while controlling for potential confounding variables. METHODS: Nine participants (mean age 30 years) with normal corneas wore a fenestrated (1 × 0.3 mm limbal fenestration) and non-fenestrated scleral lens (both lenses manufactured using a material Dk of 141 × 10-11  cm3 O2 (cm)/[(sec.)(cm2 )(mmHg)]) under open-eye conditions on separate days. Scleral lens thickness profiles were measured using a high-resolution optical coherence tomographer (OCT). Epithelial, stromal and total central corneal oedema were also measured using the OCT immediately after lens application and following 90 min of wear, prior to lens removal. RESULTS: After adjusting for differences in initial central fluid reservoir thickness and scleral lens thickness between the two lens conditions, the mean (standard error) total corrected central corneal oedema was 0.50 (0.36)% for the fenestrated lens and 0.62 (0.16)% for the non-fenestrated lens. This small difference was not statistically significant (t8  = 2.31, p = 0.81) and represents a 19% relative reduction in central corneal oedema. Similarly, epithelial (t8  = 2.31, p = 0.82) and stromal (t8  = 2.31, p = 0.92) corneal oedema were not significantly different following the fenestrated and non-fenestrated wearing conditions. CONCLUSION: Central corneal oedema in healthy corneas was comparable between fenestrated and non-fenestrated high Dk scleral lenses under short-term open-eye conditions when controlling for lens oxygen transmissibility and initial central fluid reservoir thickness.

Scleral Lens Thickness and Corneal Edema Under Closed Eye Conditions.

OBJECTIVES: To examine the relationship between central lens thickness and central corneal edema during short-term closed eye scleral lens wear. METHODS: Nine participants (mean age 30 years) with normal corneas wore scleral lenses (Dk 141) under closed eye conditions on separate days with nominal center thicknesses of 150, 300, 600, and 1,200 µm. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography immediately after lens application and after 90 min of wear, before lens removal. Data were corrected for variations in initial fluid reservoir thickness and compared with predictions from theoretical modeling of overnight scleral lens wear. RESULTS: Scleral lens-induced central corneal edema was primarily stromal in nature. The mean±standard error of corrected total corneal edema was 4.31%±0.32%, 4.55%±0.42%, 4.92%±0.50%, and 4.83%±0.22% for the 150-, 300-, 600-, and 1,200-µm lenses, respectively. No significant differences in the corrected total corneal edema were observed across all thickness groups (P=0.20). Theoretical modeling of overnight scleral lens wear seemed to overestimate the relative increase in central corneal edema as a function of decreasing lens Dk/t for values lower than 25. CONCLUSION: The magnitude of scleral lens-induced central corneal edema during short-term closed eye lens wear did not vary significantly with increasing central lens thickness. Theoretical modeling of overnight closed eye scleral lens wear seems to overestimate the effect of increasing lens thickness.

Scleral Lens Thickness and Corneal Edema Under Open Eye Conditions.

PURPOSE: To examine the relationship between lens thickness and central corneal edema during short-term open-eye scleral lens wear, and to compare these empirical edema measurements with theoretical modelling. METHODS: Nine participants (mean age 30 years) with normal corneas wore scleral lenses {Dk 141×10-11 cm3 O2 [cm]/([sec] [cm2] [mm Hg])} under open-eye conditions on separate days with nominal center thicknesses of 150, 300, 600, and 1,200 µm. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography immediately after lens application and after 90 min of wear, before lens removal. RESULTS: Central corneal edema was primarily stromal in nature and increased with increasing central lens thickness. The mean±standard error total corneal edema was 1.14±0.22%, 1.36±0.26%, 1.74±0.30%, and 2.13±0.24% for the 150, 300, 600, and 1,200 µm lenses, respectively. A significant difference in stromal and total corneal edema was observed between the 1,200 and 150 µm thickness lenses only (both P<0.05). Theoretical modelling overestimated the magnitude of central corneal edema and the influence of central lens thickness when the scleral lens Dk/t was less than 20. CONCLUSION: Scleral lens-induced central corneal edema during short-term open-eye lens wear increases with increasing central lens thickness. Theoretical models overestimated the effect of increasing scleral lens thickness upon central corneal edema for higher lens thickness values (lens Dk/t<20) when controlling for initial central fluid reservoir thickness.

Fluid Reservoir Thickness and Corneal Edema during Open-eye Scleral Lens Wear.

SIGNIFICANCE: There is debate concerning corneal oxygenation during scleral lens wear due to the potential additive hypoxic effect of a lens plus a fluid reservoir. This study investigated the agreement between theoretical models and empirical measurements of scleral lens-induced corneal edema with respect to central fluid reservoir thickness. PURPOSE: The purpose of this study was to examine the effect of altering the fluid reservoir thickness on central corneal edema during short-term open-eye scleral lens wear and to compare these empirical measurements with predictive theoretical models. METHODS: Ten participants (age, 30 ± 4 years) with normal corneas wore highly oxygen-permeable scleral lenses (141 Dk ×10 cm O2 (cm)/[(s) (cm) (mmHg)]) on separate days with either a low (mean, 144; 95% confidence interval [CI], 127 to 160 µm), medium (mean, 487; 95% CI, 443 to 532 µm), or high (mean, 726; 95% CI, 687 to 766 µm) initial fluid reservoir thickness. Epithelial, stromal, and total corneal edema were measured using high-resolution optical coherence tomography after 90 minutes of wear, before lens removal. Data were calculated or extracted from published theoretical models of scleral lens-induced corneal edema for comparison. RESULTS: Scleral lens-induced central corneal edema was stromal in nature and increased with increasing fluid reservoir thickness; mean total corneal edema was 0.69% (95% CI, 0.34 to 1.04%), 1.81% (95% CI, 1.22 to 2.40%), and 2.11% (95% CI, 1.58 to 2.65%) for the low, medium, and high thickness groups, respectively. No significant difference in corneal edema was observed between the medium and high fluid reservoir thickness groups (P = .37). "Resistance in series" oxygen modeling overestimated the corneal edema observed for fluid reservoir thickness values greater than 400 µm. CONCLUSIONS: Scleral lens-induced central corneal edema increases with increasing reservoir thickness, but plateaus at a thickness of around 600 µm, in agreement with recent theoretical modeling that incorporates factors related to corneal metabolism.

Patch-based CNN for corneal segmentation of AS-OCT images: Effect of the number of classes and image quality upon performance.

Anterior segment optical coherence tomography (AS-OCT) is a fundamental ophthalmic imaging technique. AS-OCT images can be examined by experts and segmented to provide quantitative metrics that inform clinical decision making. Manual segmentation of these images is time-consuming and subjective, encouraging software developers in the field to automate segmentation procedures. Traditional programing segmentation approaches are being replaced by deep learning methods, which have shown state-of-the-art performance in AS-OCT image analysis. In this study, a method based on patch-based convolutional neural networks (CNN) was used to segment the three main boundaries of the cornea: the epithelium, Bowman's layer, and the endothelium. To assess the effect of the number of classes on performance, the model was designed as a patch-based boundary classifier using 4 and 8 classes. The effect of image quality was also assessed using different data distributions during the training process. While the Dice coefficient and probability revealed greater precision for the 8 class models, the boundary error metric indicated comparable performance. Additionally, for 8 class models, the image quality test had only a small negative effect on performance, which may be an indication of the robustness of the model and could also suggest that the data augmentation methods did not show significant improvement. These findings contribute to the development of automatic segmentation techniques for AS-OCT images, since patch-based methods have been largely unexplored in favor of other deep learning techniques. The overall performance of the proposed method is comparable to other well-established segmentation methods.

Fluid reservoir thickness and corneal oedema during closed eye scleral lens wear.

PURPOSE: To examine the relationship between central post-lens fluid reservoir thickness and central corneal oedema during short-term closed eye scleral lens wear, and to compare these empirical oedema measurements with open eye lens wear data and current theoretical modelling for overnight scleral lens wear. METHODS: Ten participants (mean ± standard error 30 ± 1 years) with normal corneas wore scleral lenses (Dk 141 × 10-11 cm3 O2(cm)/[(sec.)(cm2)(mmHg)) under closed eye conditions on separate days with an initial central post-lens fluid reservoir thickness considered to be low (160 ± 7 µm), medium (494 ± 17 µm), or high (716 ± 16 µm). Epithelial, stromal, and total corneal oedema were measured using high-resolution optical coherence tomography immediately after lens application and following 90 min of wear, prior to lens removal. Data were compared to open eye scleral lens induced corneal oedema and a theoretical model of overnight closed eye scleral lens wear (Kim et al., 2018). RESULTS: Central corneal oedema was primarily stromal in nature and increased with increasing fluid reservoir thickness; the mean total corneal oedema was 3.86 ± 0.50%, 4.71 ± 0.28% and 5.04 ± 0.42% for the low, medium, and high thickness conditions, respectively. A significant difference in stromal and total corneal oedema was observed between the low and high fluid reservoir thickness conditions only (both p ≤ 0.01). Theoretical modelling overestimated the magnitude of central corneal oedema and the influence of fluid reservoir thickness upon corneal oedema during closed eye conditions. CONCLUSION: Scleral lens induced central corneal oedema during closed eye lens wear increases with increasing fluid reservoir thickness, but at a decreased rate compared to theoretical modelling.

Conjunctival prolapse during open eye scleral lens wear.

PURPOSE: To investigate the incidence and peak elevation of conjunctival prolapse during short-term open eye scleral lens wear and its association with lens fitting characteristics. METHODS: Ten young, healthy adults (mean age ± SD, 30 ± 4 years) wore a high Dk sealed scleral lens for 90 min with an initial central post-lens fluid reservoir thickness defined as low (144 ± 23 µm), medium (487 ± 63 µm), and high (726 ± 55 µm). Optical coherence tomography was used to quantify limbal clearance, lens settling, and changes in conjunctival thickness. RESULTS: The incidence of conjunctival prolapse was 37% across all fluid reservoir thickness conditions, with 80% of participants exhibiting conjunctival prolapse at least once. Prolapse was observed more frequently nasally (73%) than temporally (27%) (p < 0.01). The peak prolapse elevation did not vary with fluid reservoir thickness condition or anatomical location (both p > 0.05). For the low fluid reservoir thickness condition, eyes with conjunctival prolapse had greater initial limbal clearance (97 ± 38 µm compared to 43 ± 34 µm, p = 0.01) and more settling after 90 min of lens wear (-85 ± 30 µm compared to -34 ± 29 µm, p < 0.01). Greater limbal settling was associated with a higher peak elevation of the conjunctival prolapse (r = 0.48, p = 0.02), but not with landing zone tissue compression (r = 0.22, p = 0.33) or the initial or final limbal fluid reservoir thickness asymmetry (r ≤ 0.07, p > 0.05). CONCLUSION: Conjunctival prolapse was commonly observed during short-term sealed scleral lens wear in healthy eyes. The peak elevation of the conjunctival prolapse was associated with the extent of limbal settling, but not landing zone tissue compression or fluid reservoir thickness asymmetry.

Anterior segment optical coherence tomography scanning protocols and corneal thickness repeatability.

PURPOSE: To examine the influence of anterior segment optical coherence tomography imaging protocols on the intraobserver and intrasession repeatability of epithelial, stromal, and total corneal thickness measurements. METHODS: Repeated anterior segment optical coherence tomography (AS-OCT) images (Spectralis, Heidelberg) were obtained from 15 adults using single 8.3 mm wide horizontal line scans with an average of 2, 10, 20, 30, 50 and 100 B-scans. Volumetric scans consisting of nine 8.3 mm horizontal line scans encompassing a 1.3 mm vertical region were also captured (with 20 B-scans per line scan). Single point thickness measures (at the normal to the tangent of the anterior corneal surface) were compared with thickness measures averaged over the central 6 mm. The impact of B-scan averaging and intraobserver variability were examined for single line scans. For volumetric scans, the impact of the number of line scans upon intraobserver and intrasession variability were calculated. RESULTS: Intraobserver repeatability did not vary significantly as a function of the number of averaged B-scans per line scan, but was lowest for 20-30 averaged B scans. For volumetric scans, increasing the number of line scans did increase scan duration (p < 0.001), with minimal impact upon the average scan quality index (p = 0.06). Averaging more than 3 line scans did not significantly improve intraobserver or intrasession repeatability for either single point or average thickness measurements. CONCLUSION: AS-OCT volumetric scans with 3 lines each consisting of 20 B-scans with measurements averaged over a central 6 mm of the cornea provide highly repeatable measures of epithelial, stromal and total corneal thickness (95 % LoA ≤ ±3.2 µm for intraobserver repeatability and ≤ ±3.7 µm for intrasession repeatability). This scanning protocol can provide reliable information when monitoring subtle changes in corneal thickness.