Changes in the 3D Corneal Structure and Morphogeometric Properties in Keratoconus after Corneal Collagen Crosslinking

Abstract

Keratoconus is an ectatic disorder that is presently considered one of the most prevalent reasons for keratoplasty. Corneal collagen crosslinking (CXL) is the only proven treatment option available that is capable of halting the progression of the disease by stabilizing the cone in 90% of cases, and by also reducing refractive error and maximal keratometry. This study assesses, by means of a 3D morphogeometric analysis procedure developed by our research team, the corneal structure changes that occur immediately after CXL treatment and during a 6 month follow-up period. A total of 19 eyes from 19 patients diagnosed with keratoconus who underwent CXL were included, and several variables derived from the morphogeometric analysis were calculated and evaluated for the pre-operative, 3 month postoperative, and 6 month postoperative states. Significant reductions were detected in central corneal thickness and corneal spherical-like root mean square (RMS) 3 months after surgery, with non-significant regression of the effect afterward. Significant reductions in the total corneal area/volume were found, with some levels of regression after 6 months in certain volumetric parameters. In conclusion, the eyes with higher values for morphogeometric parameters—posterior apex deviation (PAD), anterior minimum thickness point deviation (AMTPD), and posterior minimum thickness point deviation (PMTPD)—seemed more likely to undergo aberrometric improvement as a result of CXL surgery.

Evidence of a Down Syndrome Keratopathy: A Three-Dimensional (3-D) Morphogeometric and Volumetric Analysis

“…Centre of mass coordinates (x, y, z) of the cornea were significantly different in patients with DS from those of the non-DS controls, where the z value was higher and x, y values were lower in the DS group. This behaviour (increase of z coordinate along with a reduction of x and y coordinates) has already been observed for the most advanced stages of KC in non-DS subjects [ 19 , 20 ], and can be explained by the fact that the deformation suffered by both corneal surfaces generates a cone-like bulge that makes the centre of mass displace in the direction of the z coordinate. The higher this deformation, the most likely it is that apices and MCT coordinates tend to “realign” with the origin of coordinates, and therefore x and y diminish.…”

“…With this configuration, a point cloud was generated for the zone that started in the cornea’s geometric centre (r = 0 mm) and reached the mid-peripheral area (r = 4 mm). This area of study typically includes most of the biometrical information of the cornea, not only for healthy eyes, but also for diseased ones [ 16 , 17 , 19 , 20 , 21 ].…”

“…By means of this software, the 3D custom model representing the corneal biometry was generated, and the following morphogeometric parameters could be calculated: anterior/posterior apex deviation from the geometrical axis (D apexant /D apexpost ); anterior/posterior minimum thickness points deviation from the geometrical axis (D mctant /D mctpost ); anterior corneal surface (ACS) area (A ant ); posterior corneal surface (PCS) area (A post ); total corneal surface area (A tot ); area of the cornea within the sagittal plane passing through the Z axis and the anterior apex/posterior apex/posterior minimum thickness point (A apexant /A apexpost /A mctpost ); centre of mass coordinates X,Y and Z (C x , C y , C z ); total corneal volume (V total ); volume between the solid corneal model and a cylinder with radius “x” (from 0.1 to 1.5 mm) and axis defined by the perpendicular line to the plane that is tangent to the anterior/posterior corneal surface at the apex (VOL AAP /VOL PAP ); and volume between the solid corneal model and a cylinder with radius “x” (from 0.1 to 1.5 mm) and axis defined by the line joining points of minimum corneal thickness of both ACS and PCS (VOL MCT ). All these indices have already been exhaustively described and used in precedent research from our group [ 16 , 17 , 19 , 20 , 21 , 22 ].…”

Relationship between Corneal Morphogeometrical Properties and Biomechanical Parameters Derived from Dynamic Bidirectional Air Applanation Measurement Procedure in Keratoconus

“…The parameters finally used in this study as well as their concept and details have been previously described in several studies of our research group [ 1 , 2 , 3 , 4 ]. More precisely, this is the case of the volumetric parameters directly related with volumes around anterior and posterior apices and minimum thickness points used hereafter [ 3 ] ( Figure 2 ): A ant is the area of the anterior corneal surface [ 1 , 2 , 4 ]; A post is the area of the posterior corneal surface [ 1 , 2 , 4 ]; CV is the total corneal volume [ 1 , 2 , 4 ]; the sagittal plane apex area (mm 2 ) is the area of the cornea within the sagittal plane passing through the Z axis and the highest point (apex) of the anterior (A apexant ) or posterior (A apexpost ) corneal surface [ 2 ]; the sagittal plane area at minimum thickness point (mm 2 ) is the area of the cornea within the sagittal plane passing through the Z axis and the minimum thickness point of the anterior (A mctant ) and posterior (A mctpost ) corneal surfaces [ 2 ]; the anterior (AAD) and posterior apex deviation (PAD) (mm) are the average distance from the Z axis to the highest point (apex) of the anterior/posterior corneal surfaces [ 2 ]; anterior (AMTPD) and posterior minimum thickness point deviation (PMTPD) (mm) are the average distance in the XY plane from the Z axis to the minimum thickness points (maximum curvature) of the anterior/posterior corneal surfaces [ 1 , 2 , 3 , 4 , 5 ]; VOL MCT is the volume contained in the intersection between the solid model of the cornea and a cylinder of revolution with radius × (from 0.1 to 1.5 mm) and its axis is defined by the points of minimum corneal thickness of the anterior and posterior corneal surface [ 1 , 2 , 3 , 4 , 5 ]; VOL AAP is the volume contained in the intersection between the solid model of the cornea and a cylinder of revolution with radius × (from 0.1 to 1.5 mm) and its axis...…”

“…This analysis has led to the development of new indices that allow a sensitive and specific detection of keratoconus, even in subclinical stages [ 1 , 2 , 3 ]. Likewise, this type of analysis has been also used and has demonstrated its usefulness when evaluating and understanding the morphogeometrical changes occurring after some surgical procedures to treat keratoconus [ 5 ]. However, the relationship between morphogeometric data and corneal biomechanical properties in keratoconus has not been investigated in depth, one of the reasons being the difficulty in obtaining reliable in-vivo corneal biomechanical data [ 6 ].…”