Phase retardation and corneal sublayer thickness repeatability using ultrahigh-resolution polarization-sensitive OCT

Patil, Rahul; Shetty, Rohit; Patel, Yash; Pisharody, Anchana; Narasimhan, Raghav; Pircher, Michael; Hitzenberger, Christoph K.; Nuijts, Rudy M.M.A.; Roy, Abhijit Sinha

doi:10.1097/j.jcrs.0000000000001033

Cited by 5 publications

(7 citation statements)

References 30 publications

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“…Measuring not only the backscattering of light, but also the birefringence properties of the cornea, which are also dependent on its collagen structure, could provide new indices for disease characterization. A recent study demonstrated the excellent repeatability of phase retardation measurements with polarization-sensitive OCT, and better repeatability of epithelial thickness measurements than spectral domain OCT 33 . It is possible that combining different imaging modalities that measure different properties of the cornea could increase the accuracy in disease detection and the diagnosis of progression in keratoconus 30 , 34 .…”

Section: Discussionmentioning

confidence: 99%

The intra- and inter-day repeatability of corneal densitometry measurements in subjects with keratoconus and in healthy controls

Gustafsson

Bizios

Ivarsen

et al. 2023

Sci Rep

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The healthy cornea is transparent, however, disease can affect its structure, rendering it more or less opaque. The ability to assess the clarity of the cornea objectively could thus be of considerable interest for keratoconus patients. It has previously been suggested that densitometry can be used to diagnose early keratoconus, and that the values of densitometry variables increase with increasing disease severity, indicating that densitometry could also be used to assess progressive keratoconus. Previous studies have only assessed the repeatability of corneal densitometry measurements on the same day, which does not reflect the clinical setting in which changes are evaluated over time. We have therefore evaluated the inter-day repeatability of densitometry measurements in both patients with keratoconus and healthy controls. Measurements in the middle layer of the 2–6 mm zone of the cornea showed the best repeatability. Although an objective measure of the corneal transparency could be interesting, the generally poor repeatability of densitometry measurements limits their use. The repeatability of corneal clarity measurements could be improved by using other approaches such as optical coherence tomography, but this remains to be investigated. Such improvements would allow the more widespread use of corneal densitometry in clinical practice.

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Section: Discussionmentioning

confidence: 99%

The intra- and inter-day repeatability of corneal densitometry measurements in subjects with keratoconus and in healthy controls

Gustafsson

Bizios

Ivarsen

et al. 2023

Sci Rep

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“…Corneal layer thickness profiles across five different zones between 2–10 mm were also generated. Further details on generation of layer thickness mapping can be found in our previous work [ 12 ]. The PR and thickness en-face maps were smoothened by applying a floating average filter equivalent to 1 mm × 1 mm area of the cornea.…”

Section: Methodsmentioning

confidence: 99%

“…PS-OCT provides additional contrast by recording of tissue specific polarization changes [ 10 ]. Thereby, enabling measurement of phase retardation (PR) caused by form birefringence in aligned and reinforcing collagen fibrils [ 9 – 12 ]. We have evaluated asymmetric keratoconus in an earlier study and the findings were clearly able to differentiate between sub-clinical and clinical disease based on PR mapping [ 9 ].…”

Section: Introductionmentioning

confidence: 99%

“…We have evaluated asymmetric keratoconus in an earlier study and the findings were clearly able to differentiate between sub-clinical and clinical disease based on PR mapping [ 9 ]. Repeatability of corneal PR maps across healthy volunteers was also demonstrated [ 12 ]. In a recent study, posterior scleral birefringence was evaluated as a biomarker for predicting the risk of myopia progression [ 13 ].…”

Section: Introductionmentioning

confidence: 99%

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Insights into atypical segmental layer thicknesses and phase retardation in thick corneas using ultrahigh-resolution polarization-sensitive optical coherence tomography

Patil,

Shetty,

Khamar

et al. 2024

Eye and Vis

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Background Accurately assessing corneal structural status is challenging when thickness deviates from the average. Polarization-sensitive optical coherence tomography (PS-OCT) measures tissue-specific polarization changes, providing additional contrast for accurate segmentations and aids in phase retardation (PR) measurements. Previous studies have shown PR's effectiveness in identifying sub-clinical keratoconus (KC) in asymmetric cases. Thus, this study aims to assess PR distribution in thick corneas with and without KC. Methods In this retrospective and cross-sectional study, 45 thick corneas from 30 Asian-Indian subjects, categorized into healthy (n = 26) and KC (n = 19) groups were analyzed. All eyes underwent standard clinical evaluations, tomographic assessments, and corneal biomechanics measurements. PR and individual layer thicknesses were measured using custom-designed ultrahigh-resolution PS-OCT. PR en-face maps were generated. Individual layer thicknesses and PR analysis was conducted across multiple zones, extending up to 8–10 mm in diameter. All eyes in the study had not undergone interventions, received topical medications, or had previous corneal disease history. Results Significant differences were found in spherical and cylindrical powers, keratometry, pachymetry, and biomechanical indices (all P < 0.01). Thickness profiles from PS-OCT showed significant differences in the 4–8 mm zones only. Bowman's layer thickness significantly differed only in the central 2 mm zone (P = 0.02). The median PR values showed marginal differences in the central 2 mm zone (P = 0.0565). Additionally, there were significant differences observed in the 2–4 mm and 4–6 mm zones (P = 0.0274 and P = 0.0456, respectively). KC eyes exhibited an atypical PR distribution and corneal thinning, while normal eyes maintained a uniform Bowman’s layer thickness and PR maps with larger areas of higher PR. Conclusion The study revealed distinctive PR distribution in thick corneas among healthy and KC groups. Using an ultrahigh-resolution PS-OCT the significance of Bowman's layer thickness in these groups was also emphasized. The study offered potential improvements in clinical diagnostics by enhancing our understanding of corneal structure and its altered function.

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“…In an earlier study, corneal phase retardation was reported to be sensitive to discriminate early KC [56]. Recent studies evaluated corneal phase retardation in healthy, thin, asymmetric KC, and clinical KC corneas, and showed higher phase retardation in clinical KC eyes [57,58].…”

Section: Anterior Segment Optical Coherence Tomographymentioning

confidence: 98%

Multi-modal imaging for the detection of early keratoconus: a narrative review

Al Bdour,

Sabbagh,

Jammal

2024

Eye and Vis

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Keratoconus is a common progressive corneal disorder that can be associated with significant ocular morbidity. Various corneal imaging techniques have been used for the diagnosis of established cases. However, in the early stages of the disease, which include subclinical keratoconus and forme fruste keratoconus, detection of such cases can be challenging. The importance of detecting such cases is very important because early intervention can halt disease progression, improve visual outcomes and prevent postrefractive surgery ectasia associated with performing corneal refractive procedures in such patients. This narrative review aimed to examine several established and evolving imaging techniques for the detection of early cases of keratoconus. The utilization of combinations of these techniques may further increase their diagnostic ability.

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Phase retardation and corneal sublayer thickness repeatability using ultrahigh-resolution polarization-sensitive OCT

Cited by 5 publications

References 30 publications

The intra- and inter-day repeatability of corneal densitometry measurements in subjects with keratoconus and in healthy controls

The intra- and inter-day repeatability of corneal densitometry measurements in subjects with keratoconus and in healthy controls

Insights into atypical segmental layer thicknesses and phase retardation in thick corneas using ultrahigh-resolution polarization-sensitive optical coherence tomography

Multi-modal imaging for the detection of early keratoconus: a narrative review

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