3-D assessment of gaze-induced eye shape deformations and downgaze-induced vitreous chamber volume increase in highly myopic eyes with staphyloma

Understanding Posterior Staphyloma in Pathologic Myopia: Current Overview, New Input, and Perspectives

Posterior staphyloma (PS) is considered the hallmark of pathologic myopia and is defined as an outpouching of a circumscribed portion of the eyeball with a radius of curvature smaller than that of the adjacent zone. Although more common in eyes with high myopia, it can affect those without it. The presence of PS is associated with a structurally and functionally worse course of high myopia that can lead to visual disability. Unfortunately, the pathogenesis of PS is unclear so far. Thus, due to the increasing prevalence of myopia which has been further exacerbated by the advent of COVID-19 lockdown, researchers are eager to elucidate the pathogenesis of pathologic myopia and that of its complications, especially PS, which will allow the development of preventive strategies. The aim of this work was to review the morphological characteristics of PS with emphasis on similarities with peripapillary staphyloma and to discuss the pathogenesis of PS considering recent suggestions about that of peripapillary staphyloma.

Fully Automated Segmentation of Human Eyeball Using Three-Dimensional U-Net in T2 Magnetic Resonance Imaging

Purpose

To develop and validate a fully automated deep-learning-based tool for segmentation of the human eyeball using a three-dimensional (3D) U-Net, compare its performance to semiautomatic segmentation ground truth and a two-dimensional (2D) U-Net, and analyze age and sex differences in eyeball volume, as well as gaze-dependent volume consistency in normal subjects.

Methods

We retrospectively collected 474 magnetic resonance imaging (MRI) scans, including different gazing scans, from 119 patients. A 10-fold cross-validation was applied to separate the dataset into training, test, and validation sets for both the 3D U-Net and 2D U-Net. Performance accuracy was measured using four quantitative metrics compared to the ground truth, and Bland-Altman plot analysis was conducted. Age and sex differences in eyeball volume and variability in eyeball volume differences across gazing directions were analyzed.

Results

The 3D U-Net outperformed the 2D U-Net with mean accuracy scores >0.95, showing acceptable agreement in the Bland-Altman plot analysis despite a tendency for slight overestimation (mean difference = -0.172 cm³). Significant sex differences and age effects on eyeball volume were observed for both methods (P < 0.05). No significant volume differences were found between the segmentation methods or within each method for the different gazing directions. Significant differences in performance accuracy were identified among the five gazing directions, with the upward direction showing a notably lower performance.

Conclusions

Our study demonstrated the effectiveness of 3D U-Net human eyeball volume segmentation using T2-weighted MRI. The robustness and reliability of 3D U-Net across diverse populations and gaze directions support enhanced ophthalmic diagnosis and treatment strategies.

Translational Relevance

Our findings demonstrate the feasibility of using the proposed 3D U-Net model for the automatic segmentation of the human eyeball, with potential applications in various ophthalmic research fields that require the analysis of 3D geometric eye globe shapes or eye movement detection.

Ultrasound Assessment of Gaze-induced Posterior Eyewall Deformation in Highly Myopic Eyes

Purpose

To establish a quantitative metric of posterior eyewall deformability in different directions of gaze in highly myopic eyes with and without posterior staphyloma.

Methods

A prospective study was performed on 53 highly myopic patients (106 eyes). Ultrasound scans were acquired in primary, up, downward, nasal, and temporal gazes. A validated intensity-based segmentation algorithm was used to quantify the posterior eyewall geometry on digitalized B-scan images. Posterior eyewall local curvature (K) and distance (L) to the transducer were calculated. The associations between directions of gaze, axial length (AL), and presence of staphyloma with the K and L parameters were assessed.

Results

A total of 53 participants (106 eyes) were studied. Multivariate regression analysis demonstrated that, after accounting for longer AL, and presence of staphyloma, eccentric gaze was often independently associated with various K and L parameters. Specifically, downward gaze was associated with increased posterior eyewall concavity as reflected in the maximum of K (KMax) (β = 0.050, P < 0.001) and absolute value of KMax (β = 0.041, P = 0.011). Both downward gaze and upgaze were independently associated with increase in the derivative of absolute KMax (which is consistent with more apparent, steeper staphyloma ridges), local KMax (which detects KMax at smaller intervals), and Kstd (which represents likelihood of staphyloma presence) and decrease in maximum of L (which represents movement of the staphyloma apex) with all P < 0.05. The β coefficients for downward gaze were consistently greater in magnitude compared with those in upgaze. After accounting for AL and presence of staphyloma, horizontal gazes were independently associated only with decrease in the standard deviation of L (which also represents likelihood of staphyloma presence) and maximum of L.

Conclusions

Downward gaze results in a significant increase in posterior eyewall concavity in highly myopic eyes after accounting for AL and staphyloma presence. In comparison with downward gaze, upgaze resulted in a lower magnitude, but significant changes in staphyloma ridge steepness and the likelihood of staphyloma presence. Horizontal gazes seemed to be associated with less posterior eyewall geometric parameters. Studies are required to further assess the association between downward gaze during near work on posterior eyewall concavity and possible effects on myopia development and progression.

Automated Classification and Detection of Staphyloma with Ultrasound Images in Pathologic Myopia Eyes

The aim of this study was to develop an eyewall curvature- and axial length (AxL)-based algorithm to automate detection (clinician-free) of staphyloma ridge and apex locations using ultrasound (US). Forty-six individuals (with emmetropia, high myopia or pathologic myopia) were enrolled in this study (AxL range: 22.3-39.3 mm), yielding 130 images in total. An intensity-based segmentation algorithm automatically tracked the posterior eyewall, calculating the posterior eyewall local curvature (K) and distance (L) to the transducer and the location of the staphyloma apex. By use of the area under the receiver operator characteristic (AUROC) curve to evaluate the diagnostic ability of eight local statistics derived from K, L and AxL, the algorithm successfully quantified non-uniformity of eye shape with an AUROC > 0.70 for most K-based parameters. The performance of binary classification (staphyloma absence vs. presence) was assessed with the best classifier (the combination of AxL, standard deviation of K and standard deviation of L) yielding a diagnostic validation performance of 0.897, which was comparable to the diagnostic performance of junior clinicians. The staphyloma apex was localized with an average error of 1.35 ± 1.34 mm. Combined with the real-time data acquisition capabilities of US, this method can be employed as a screening tool for clinician-free in vivo staphyloma detection.

Ultrawide field, distortion-corrected ocular shape estimation with MHz optical coherence tomography (OCT)

Ocular deformation may be associated with biomechanical alterations in the structures of the eye, especially the cornea and sclera in conditions such as keratoconus, congenital glaucoma, and pathological myopia. Here, we propose a method to estimate ocular shape using an ultra-wide field MHz swept-source optical coherence tomography (SS-OCT) with a Fourier Domain Mode-Locked (FDML) laser and distortion correction of the images. The ocular biometrics for distortion correction was collected by an IOLMaster 700, and localized Gaussian curvature was proposed to quantify the ocular curvature covering a field-of-view up to 65°×62°. We achieved repeatable curvature shape measurements (intraclass coefficient = 0.88 ± 0.06) and demonstrated its applicability in a pilot study with individuals (N = 11) with various degrees of myopia.

Optic nerve tortuosity and displacements during horizontal eye movements in healthy and highly myopic subjects

AIMS

(1) To assess the morphology and 3-dimensional (3D) displacements of the eye globe and optic nerve (ON) in adduction/abduction using MRI. (2) To assess differences between healthy emmetropic and highly myopic (HM) subjects.

METHODS

MRI volumes of both eyes from 18 controls and 20 HM subjects in primary gaze, abduction and adduction (15°) were postprocessed. All ONs were manually segmented and fitted to a 3D curve to assess ON tortuosity. ON displacements were evaluated in four quasicoronal planes which were perpendicular to the ON in primary gaze and were 3 mm apart.

RESULTS

Axial length was higher in the HM group (28.62±2.60 vs 22.84±0.89 mm; p<0.0001). Adjusted ON tortuosities (ie, ON tortuosities estimated before myopia onset) were lower in HM eyes (0.9063±0.0591) versus controls (1.0152±0.02981) in primary gaze, adduction (0.9023±0.05538 vs 1.0137±0.0299) and abduction (0.9100±0.0594 vs 1.0182±0.0316); p<0.0001 for all cases. In all eyes, ON displacements in adduction were significantly different from those in abduction in the naso-temporal direction (p<0.0001 in all planes) but not in the supero-inferior direction. ON displacements in the posterior segments of the ON were smaller in the HM group in both gaze directions and were larger in the anterior-most ON segment in adduction only.

CONCLUSION

The adjusted tortuosity of the ON was significantly lower in HM eyes, suggesting that eyes destined towards HM exhibited higher ON traction forces during eye movements before the onset of myopia. Our ON metrics may be valuable to explore a potential link between eye movements and axial elongation.