Patil Rahul P, Shetty Rohit, Khamar Pooja, Patel Yash G, Narasimhan Raghav R, Bhatkal Anushree A, Hitzenberger Christopher K, Pircher Michael, Nuijts Rudy M M R, Sinha Roy Abhijit
Imaging, Biomechanics and Mathematical Modelling Solutions Lab, Narayana Nethralaya Foundation, Narayana Nethralaya, Bangalore, India.
University Eye Clinic Maastricht, Maastricht University Medical Center, Maastricht, The Netherlands.
Eye Vis (Lond). 2024 Jul 15;11(1):30. doi: 10.1186/s40662-024-00391-4.
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.
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.
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.
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.
当角膜厚度偏离平均值时，准确评估角膜结构状态具有挑战性。偏振敏感光学相干断层扫描（PS-OCT）可测量组织特异性偏振变化，为精确分割提供额外对比度，并有助于相位延迟（PR）测量。先前的研究表明，PR在识别不对称病例中的亚临床圆锥角膜（KC）方面具有有效性。因此，本研究旨在评估有和没有KC的厚角膜中的PR分布。
在这项回顾性横断面研究中，分析了30名亚洲印度受试者的45只厚角膜，分为健康组（n = 26）和KC组（n = 19）。所有眼睛均接受了标准临床评估、断层扫描评估和角膜生物力学测量。使用定制设计的超高分辨率PS-OCT测量PR和各层厚度。生成PR正面图。在多个区域进行各层厚度和PR分析，直径延伸至8 - 10毫米。研究中的所有眼睛均未接受过干预、局部用药或有既往角膜疾病史。
在球镜和柱镜度数、角膜曲率、角膜厚度测量和生物力学指标方面均发现显著差异（所有P < 0.01）。PS-OCT的厚度剖面图仅在4 - 8毫米区域显示出显著差异。Bowman层厚度仅在中央2毫米区域有显著差异（P = 0.02）。PR中位数在中央2毫米区域显示出微小差异（P = 0.0565）。此外，在2 - 4毫米和4 - 6毫米区域也观察到显著差异（分别为P = 0.0274和P = 0.0456）。KC眼睛表现出非典型的PR分布和角膜变薄，而正常眼睛保持均匀的Bowman层厚度和PR图，且较高PR区域面积更大。
该研究揭示了健康组和KC组厚角膜中独特的PR分布。使用超高分辨率PS-OCT还强调了这些组中Bowman层厚度的重要性。该研究通过增强我们对角膜结构及其改变功能的理解，为临床诊断提供了潜在的改进。
