Scheimpflug Densitometry in Keratoconus: A New Method of Visualizing the Cone

Abstract

Purpose: To report an observation made while performing Scheimpflug densitometry analysis on the corneal region affected in keratoconus (KC) that seems to delineate the base of the cone. Methods: Scheimpflug densitometries of 20 healthy subjects and 90 patients with KC were examined. Corneal densitometry was analyzed using both “1-layer” and “2-layer” approaches. The first considers the corneal transparency layer by layer at different depths, whereas the second averages densitometry between 2 corneal layers selected by the examiner. Fixed layers, 120 μm depth, and endothelium were selected. Repeated same-day scans and longitudinal series of scans were also evaluated to see whether the findings evolved over time. Results: Eighty-eight of 90 KC cases displayed a bright area on the densitometry map that corresponded to the cone location. The area's characteristics, such as its brightness, contrast, and the presence of a delimiting arc correlated with KC severity and was more noticeable in advanced cases. No similar marks were found in any of the normal subjects. The shape, location, and extent of the mark were consistent over consecutive measures taken on the same day. Changes over time were also seen in eyes with known clinical progression but was also seen in eyes considered clinically stable. Conclusions: The densitometry mark seems to correspond with the zone most affected by KC and could be a supplementary tool for documenting KC stage, alongside conventional parameters. Further studies are required to ascertain whether it could prove useful in KC detection, to determine progression, and to relate it to corneal biomechanical behavior.

Densitometry marks delineating the affected area in keratoconus: clinical suitability of a new descriptive system based on its repeatability and reproducibility

“…The 'one-layer' and 'two-layers' scan method to obtain the images was reported in a previous study. 11 'Two-layers' scans of 50 patients constitute the map set subject to analysis. For the purposes of consistency, Layer 1 was always chosen as the first value ≥120 µm (i.e., excluding epithelium, Bowman's layer and anterior stroma) and the endothelium was chosen as Layer 2.…”

“…[7][8][9][10] We recently reported an observation that appears to delineate the cone in KC based on densitometry marks seen on Scheimpflug tomography. 11 The major advantage of the bright densitometry marks over classical tomographic maps is that it relies only on the light's transmission properties. While the classical maps are founded on calculations and assumptions, densitometry maps are based on raw data, and therefore no assumptions about corneal refractive index, geometrical optics, etc.…”

“…We recently reported an observation that appears to delineate the cone in KC based on densitometry marks seen on Scheimpflug tomography 11 . The major advantage of the bright densitometry marks over classical tomographic maps is that it relies only on the light's transmission properties.…”

Detection of Subclinical Keratoconus With a Validated Alternative Method to Corneal Densitometry

“… 12 Recently, and in agreement with the findings of Lopes et al, 13 our group reported that densitometry might be used to accurately demarcate the location of clinical keratoconus. 14 One of the major drawbacks of densitometry, however, is that, to date, it is exclusively available on one single commercial device. To overcome this limitation, our research group introduced densitometry distribution analysis (DDA), 15 which is a platform-independent methodology based on the statistical modeling of the pixel intensity distribution of Scheimpflug images that correlates very well with traditional densitometry (overall cornea, r = 0.89; P < 0.001).…”

Forecasting Progressive Trends in Keratoconus by Means of a Time Delay Neural Network

“…Keratoconus (KC) is a progressive, ectatic corneal disorder presenting with central or paracentral stromal thinning associated, among others, with corneal protrusion, structural changes, and transparency loss [ 1 , 2 , 3 ]. The condition has a multifactorial etiology, attributable to a genetic predisposition, eye rubbing, or biomechanical factors [ 4 ], and a cascade of biomechanical decompensation triggered by a focal change in corneal elasticity is thought to be responsible for KC progression [ 5 ].…”