Large Field of View Corneal Epithelium and Bowman's Layer Thickness Maps in Keratoconic and Healthy Eyes

Pircher, Niklas; Beer, Florian; Stephan, Holger; Gschließer, Andreas; Donner, René; Pircher, Michael; Hitzenberger, Christoph K.; Schmidinger, Gerald; Lammer, Jan

doi:10.1016/j.ajo.2019.05.025

Cited by 18 publications

(13 citation statements)

References 23 publications

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“…However, accurately diagnosing KC in the early stage is still a major clinical challenge. Decreases in corneal biomechanics and thinning of the corneal epithelium have been proposed to occur earlier than tissue loss and topographic alterations in KC patients; thus, measuring the corneal biomechanics and epithelial thickness has been reported to aid in the early diagnosis of KC [15][16][17][18][25][26][27][28]. Our findings regarding alterations in the corneal tomography, biomechanics and epithelial thickness in AC patients are consistent with the changes in patients with early KC.…”

Section: Discussionsupporting

confidence: 85%

“…In KC patients, corneal epithelial remodeling and thinning in the cone area have been reported to maintain a smooth corneal surface and mask the already ongoing stromal protrusion, resulting in the delayed detection of KC [28]. Measurement of the epithelial thickness has been proven to aid in the early diagnosis of KC [25][26][27]. To the best of our knowledge, this is the first study to reveal corneal epithelial thinning and an uneven corneal thickness distribution in AC patients, indicated by a thinner average corneal epithelial thickness with greater variation.…”

Section: Discussionmentioning

confidence: 99%

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Corneal biomechanical changes in allergic conjunctivitis

Wang

Deng

et al. 2021

Eye and Vis

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Background To explore corneal biomechanical changes, identify related factors and determine early indicators of keratoconus (KC) development risk in allergic conjunctivitis (AC) patients. Methods A total of 50 patients, including 20 eyes without AC and 30 eyes with AC were enrolled in this study. All patients underwent a complete ocular examination, including evaluations of clinical manifestations of AC, corneal tomography and densitometry by Pentacam, corneal biomechanics by Corvis ST, and corneal and epithelial thickness mapping by RTvue optical coherence tomography (OCT). Results The index of surface variance (ISV), index of vertical asymmetry (IVA), keratoconus index (KI), index of height decentration (IHD) and Belin/Ambrosio enhanced ectasia total deviation index (BAD-D) were significantly higher in the AC group than in the non-allergic conjunctivitis (NAC) group (P < 0.05). The tomography and biomechanical index (TBI) was also significantly higher in the AC group (P = 0.04). The average epithelial thickness in the 2–7 mm annulus was significantly thinner in the AC group than in the NAC group (P < 0.05). The average densitometry of the total cornea and the anterior layer were higher in the AC group than in the NAC group (P < 0.001). The ISV, IVA, KI, IHD and BAD-D were significantly correlated with the TBI and changes in corneal epithelial thickness in AC patients (P < 0.05). The changes in epithelial thickness were closely related to the eye rubbing frequency and allergic sign scores (P < 0.05). Conclusions AC patients should be advised to routinely undergo corneal tomographic and biomechanical measurements, and the TBI could be used as an indicator of KC development risk in AC patients. Trial registration Corneal Biomechanical Changes of Allergic Conjunctivitis, NCT04299399. Registered March 3, 2020 - Retrospectively registered.

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Section: Discussionsupporting

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Corneal biomechanical changes in allergic conjunctivitis

Wang

Deng

et al. 2021

Eye and Vis

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“…For Brillouin measurements performed on intact eye globes, both in vivo and ex vivo, this sensitivity must be taken into account as the frequency shift will be dependent on the angle of the collagen fibers, thereby, the natural curvature of the eye. Therefore, similar to the recently developed polarization-sensitive (PS)optical coherence tomography (OCT), which compensates for scanning angle-induced artifacts, 56,57 en face Brillouin maps of the cornea can be normalized based on the angle dependence of Brillouin shift found in this study. This ability to detect mechanical anisotropy also enabled us to isolate the contributions of hydration and solid mechanics on Brillouin frequency shift.…”

Section: Discussionmentioning

confidence: 99%

Detecting Mechanical Anisotropy of the Cornea Using Brillouin Microscopy

Webb

Zhang

Roy

et al. 2020

Trans. Vis. Sci. Tech.

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The purpose of this study was to detect the mechanical anisotropy of the cornea using Brillouin microscopy along different perturbation directions. Methods: Brillouin frequency shift of both whole globes (n = 10) and cornea punches (n = 10) were measured at different angles to the incident laser, thereby probing corneal longitudinal modulus of elasticity along different directions. Frequency shift of virgin (n = 26) versus cross-linked corneas (n = 15) over a large range of hydration conditions were compared in order to differentiate the contributions to Brillouin shift due to hydration from those due to stromal tissue. Results: We detected mechanical anisotropy of corneas, with an average frequency shift increase of 53 MHz and 96 MHz when the instrument probed from 0°to 15°and 30°along the direction of the stromal fibers. Brillouin microscopy did not lose sensitivity to mechanical anisotropy up to 96% water content. We experimentally measured and theoretically modeled how mechanical changes independent of hydration affect frequency shift as a result of corneal cross-linking by isolating an approximately 100 MHz increase in frequency shift following a cross-linking procedure purely due to changes of stromal tissue mechanics. Conclusions: Brillouin microscopy is sensitive to mechanical anisotropy of the stroma even in highly hydrated corneas. The agreement between model and experimental data suggested a quantitative relationship between Brillouin frequency shift, hydration state of the cornea, and stromal tissue stiffness. Translational Relevance: The protocol and model validated throughout this study offer a path for comprehensive measurements of corneal mechanics within the clinic; allowing for improved evaluation of the long-term mechanical efficacy of cross-linking procedures.

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“…Initially designed to characterize epithelial thickness in a 6-mm zone, a recent upgrade allows expansion up to 9 mm, equivalent to an area that is approximately two and a quarter times larger than the former. 2 Using a custom-designed polarization-sensitive OCT, Pircher and colleagues 3 were able to map the thickness of the Bowman’s layer in addition to the epithelium from limbus-to-limbus and noted a highly irregular “moth-like” damage pattern in the Bowman’s layer in keratoconic eyes. Another group employed a commercially available swept-source OCT and by postprocessing, delineation of the air–epithelium edge and epithelium–Bowman’s layer interface was made possible.…”

Section: Advances In Diagnosismentioning

confidence: 99%

Advances in the diagnosis and treatment of keratoconus

2021

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Keratoconus had traditionally been considered a rare disease at a time when the imaging technology was inept in detecting subtle manifestations, resulting in more severe disease at presentation. The increased demand for refractive surgery in recent years also made it essential to more effectively detect keratoconus before attempting any ablative procedure. Consequently, the armamentarium of tools that can be used to diagnose and treat keratoconus has significantly expanded. The advances in imaging technology have allowed clinicians and researchers alike to visualize the cornea layer by layer looking for any early changes that might be indicative of keratoconus. In addition to the conventional geometrical evaluation, efforts are also underway to enable spatially resolved corneal biomechanical evaluation. Artificial intelligence has been exploited in a multitude of ways to enhance diagnostic efficiency and to guide treatment. As for treatment, corneal cross-linking treatment remains the mainstay preventive approach, yet the current main focus of research is on increasing oxygen availability and developing new strategies to improve riboflavin permeability during the procedure. Some new combined protocols are being proposed to simultaneously halt keratoconus progression and correct refractive error. Bowman layer transplantation and additive keratoplasty are newly emerging alternatives to conventional keratoplasty techniques that are used in keratoconus surgery. Advances in tissue engineering and regenerative therapy might bring new perspectives for treatment at the cellular level and hence obviate the need for invasive surgeries. In this review, we describe the advances in the diagnosis and treatment of keratoconus primarily focusing on newly emerging approaches and strategies.

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Large Field of View Corneal Epithelium and Bowman's Layer Thickness Maps in Keratoconic and Healthy Eyes

Cited by 18 publications

References 23 publications

Corneal biomechanical changes in allergic conjunctivitis

Corneal biomechanical changes in allergic conjunctivitis

Detecting Mechanical Anisotropy of the Cornea Using Brillouin Microscopy

Advances in the diagnosis and treatment of keratoconus

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