Repeatability of anterior segment measurements by optical coherence tomography combined with Placido disk corneal topography in eyes with keratoconus

Abstract

corneal tomography is an important tool to identify and follow up eyes with keratoconus. our study evaluate the repeatability of the automatic measurements provided in keratoconic eyes by a new anterior-segment optical coherence tomographer (AS-oct) combined with placido-disk topography (MS-39, CSO) and assess their agreement with the corresponding measurements taken with a rotating Scheimpflug camera combined with Placido-disk topography (Sirius, CSO). Mean simulated keratometry, posterior and total corneal power, total corneal astigmatism, corneal asphericity, thinnest corneal thickness, epithelial thickness, corneal diameter, and aqueous depth were evaluated. Repeatability was assessed using test-retest variability, the coefficient of variation, and the intraclass correlation coefficient; agreement was assessed by the 95% limits of agreement. Good repeatability was achieved for most parameters. Moderate repeatability was found for total corneal astigmatism measurements. the repeatability of mean simulated keratometry and total corneal power measurements worsened with more severe stages of keratoconus with a statistically significant relationship between the individual coefficient of variation and corneal power values. Agreement with the Scheimpflug camera was moderate for aqueous depth and thinnest corneal thickness and poor for most other measured parameters. the good repeatability of automatic measurements suggests the new AS-oct device to be a viable option in clinical practice of eyes with keratoconus. Keratoconus is a non-inflammatory ectasic disease characterized by progressive thinning and steepening and an apical cone-shaped protrusion of the cornea 1,2. The introduction of corneal topography first and corneal tomography later enabled researchers to develop several methods to identify keratoconic eyes 3-7. Accurate corneal imaging is now highly desirable to diagnose keratoconus, especially in its earlier stages, when visual acuity is still good. Modern anterior segment imaging techniques, such as Scheimpflug photography and optical coherence tomography (OCT), have significantly improved our ability to identify eyes with keratoconus, as they also provide pachymetric data and posterior corneal curvature measurements. Although anterior corneal surface parameters may be sufficient to discriminate between normal eyes and eyes with clinical keratoconus, using the data from both corneal surfaces as well as corneal thickness increases precision, sensitivity, specificity, and accuracy, thus significantly improving the ability to differentiate between normal eyes and subclinical keratoconus suspect eyes 7. One of the main limitations of Scheimpflug imaging is the low resolution and relatively poor quality of anterior segment scans. In this regard, anterior segment OCT (AS-OCT) is known to produce better images with higher definition. The higher resolution has made it possible, for example, to measure the corneal epithelial thickness 8-10. A parameter that has never been evaluated by Scheimpflug cameras. The purp...

Epithelial and stromal remodelling following femtosecond laser–assisted stromal lenticule addition keratoplasty (SLAK) for keratoconus

“…MS-39 uses Spectral-domain OCT (SD-OCT) and Placido Disk corneal topography to obtain measurements from the anterior segment of the eye. The repeatability of corneal sub-layer measurements performed with this device in healthy eyes and corneas affected by keratoconus was previously reported 19,20 .…”

“…Studies using high-resolution AS-OCT confirmed these findings and were used to create a classification for the severity of keratoconus 27,28 . Anterior segment OCT combined with Placido topography (MS-39) used in this study was previously validated in normal eyes, keratoconic corneas, and eyes following excimer laser treatment 19,20 . In this study, high-resolution AS-OCT cross-sections allowed the identification of intrastromal lenticule profiles and the assessment of changes in the corneal epithelial and stromal regional thickness over time.…”

Multi-modal Anterior Eye Imager Combining Ultra-High Resolution OCT and Microvascular Imaging for Structural and Functional Evaluation of the Human Eye

“…The integration of OCT with SLB conducted by both Stehouwer et al [41] and Mueller et al [42] can image both anterior and posterior segments more efficiently but only provides structural images. Other groups have applied the combinations of OCT [43,44] or a Scheimpflug camera [45] and corneal topography with a focus only on the anterior segment biometry measurements. Compared with current ophthalmic imaging modalities, our self-developed multi-modal anterior eye imager not only offers precise structural information with the UHR-OCT module, but also provides functional information of bulbar conjunctival vessels through the microvascular imaging module.…”

“…Multi-modal systems will not only improve the examination efficiency by reducing patients' moving from one examination system to the others, but also reduce the space and equipment investment. To date, researchers have developed a variety of multi-modal systems to combine the merits of each imaging modality for human eye imaging [36][37][38][39][40][41][42][43][44][45], among which, however, most are focused on posterior segment imaging [36][37][38][39][40]. Hybrid systems for anterior human eye imaging are relatively rare: few researches have demonstrated the integration of OCT system into SLB for both anterior and posterior segment imaging to improve the examination efficiency [41,42]; multi-modal systems combining OCT and corneal topography have been developed for anterior segment biometry measurements and applied to eyes with keratoconus [43,44]; a Scheimpflug camera combined with corneal topography has been used to measure pre/post-refractive surgery eyes [45].…”

Comparative clinical accuracy analysis of the newly developed ZZ IOL and four existing IOL formulas for post-corneal refractive surgery eyes

“…First, the mean or median value of multiple measurements could be used. Second, anterior-segment OCT could be used instead of traditional corneal tomography; the higher resolution, higher definition, and relatively higher quality of anterior segment scans may produce better results [ 35 ]. Third, Placido-disk, Scheimpflug, and anterior-segment OCT protocols could all be used to measure the corneal curvature, but each has its advantages [ 36 ].…”