Detection of subclinical Keratoconus and ectasia with software preventing SCORE Analyzer.
The Score software is a computer program in artificial intelligence intended to provide assistance to the clinical decision in refractive surgery for early detection of new forms of Keratoconus infra-clinic and prevention of corneal ectasia. Designed by Dr Damien Gatinel and Alain Saad between 2009 and 2011, it has obtained the CE in December 2013. It follows from the findings of a clinical research work started in 2002, and uses the data provided by the topographer Orsbcan IIz (Bausch & Lomb, Technolas PV, Germany).
Presentation of the SCORE Analyzer software:
SCORE Analyzer software is a program of clinical decision support. A website devoted to it (in English): www.score-Analyzer.com
The software uses the data acquired by the specular topographer and elevation Orbscan IIz. SCORE software takes the classic view 'Quadmap' (4 maps) and complete it by new quantitative evidence gathered in a maps designed for a quick and easy interpretation.
SCORE Analyzer must be used for early detection of forms beginner subclinical of Keratoconus in myopic subjects, never operated in refractive surgery, less than 50 years of age: these characteristics derive from those eyes included in the control group used for the development of the software.
The value of the Score
The value of the score is the result of a discriminant function with 12 variables whose optimal threshold for sensitive and specific detection has adjusted to match the value 'zero '.
-a negative value (score < 0) corresponds to a cornea judged free form fruste of Keratoconus.
-a positive value (score > 0) corresponds to a cornea that is considered as infringement of a form fruste of Keratoconus.
The absolute value of this value (its "distance" with the threshold) is indicative of the character "normal" or "abnormal" analyzed cornea. The realization of corneal refractive surgery type LASIK is deprecated in case of positive value.
The radar is a map with the 6 topographic indices among the most discriminating used for the calculation of the score. The values of each index are brought on a demi-axe, and the 6 semi-axles linked together so that the coordinate points connected to each of the indices form a polygon. A colour scale ranging from green to red allows a quick visual analysis of the results. The yellow color is the limit value (average more or less two standard from a normal population deviations). Orange and red colors correspond to abnormal values.
The variables used in the construction of the radar are:
– L’thickness of the thinnest point (microns) that corresponds to the minimum thickness of the corneal wall (using an acoustic factor of 0.92 for the Orbscan)
– L’after maximum elevation (microns) which corresponds to the maximum distance in the Central 3mm between the corneal posterior data and calculated later reference sphere.
– L’irregularity in the Central 3mm of the anterior (dioptres) which is proportional to the standard deviation of the values taken by the local curvature of the anterior surface.
– Le vertical shift of the point the thinnest point (mm) and which is moving from the finest to the geometric center of the cornea.
– La average difference between the Central thickness (area Central diameter 2 mm) and the thinnest thickness.
-The value of the Unlike I-S (Dioptres), which corresponds to the difference between the values average IOL 5 equidistant points located 1.5 mm of the vertex at the level of the anterior corneal surface top (S) and lower (I). It reflects the degree of vertical asymmetry of the corneal surface earlier.
Thick curves (product): average thickness and thinning to the thinnest point rate (speed).
The curve of medium thickness ("averaged pachymetry") consists of the average values of the thickness of the cornea from the periphery to the Center (point the thinner), according to 9 concentric rings of width 0.5 mm, contiguous to the periphery (diameter 9 mm) to the center of the cornea (where the reporting average value is that of a central lozenge of 1 mm wide centred on the thinnest point).
The thinning rate curve corresponds to the speed of the corneal wall thinning towards the end: each value is expressed as a percentage, which reflects the reduction in thickness between two adjacent rings.
Origin of the SCORE Analyzer
Choosing a relevant clinical model
Keratoconus frustes forms are defined by some authors as of the very beginner infra-clinical forms, where the achievement of the anterior face of the cornea is not sufficiently pronounced it rising suspicion; the values taken by the indices used for testing below the detection thresholds for these.
How to study the topographical characteristics of the eyes with these forms frustes of Keratoconus? In theory, we could analyze retrospectively the ancient topographical maps, performed at the early stage of affection for eyes today suffering from Keratoconus turned out, in the hope to find the beginnings of this affection. Unfortunately, it is rare that patients have received a corneal topography, then they were visually asymptomatic, and showed no sign of appeal to review biomicroscopique (slit lamp).
Another clinical model can be used to track down the most beginner forms of Keratoconus: eyes are less affected patients achieved "very asymmetrical Keratoconus between the eyes., IE advanced (clinical and/or topographic form proved) over one eye, and very beginner on the other (i.e. objectively subclinical, with) negativity of detection based on topography specular Placido mode's clues). The least reached eye was included within the Group of interest of our clinical model, if from testing of the specular topography (ex: Klyce - Maeda criteria) were negative, meaning that the automatic classification by neural network (Corneal Navigator, surveyor OPDScan, Nidek, Japan) provided similar percentages strictly Dummies for the objective topographic diagnosis of Keratoconus turned out suspect Keratoconus and pellucid marginal degeneration,.. .so that the other eye was of course tested positive for the diagnosis of Keratoconus turned out.
This clinical model is valuable because it allows you to establish a group of eyes which it is certain (through the achievement of the other eye) they correspond to a fledgling form of Keratoconus () subclinical1). The existence of strictly unilateral forms of Keratoconus is denied by most of the authors)2,3) It may be considered more relevant to include these diagnostic eyes as ' normal»(par erreur, ou plutôt car à un stade très débutant – inférieur àle seuil retenus pour les critères Placido), eyes which would be directly diagnosed as 'Keratoconus suspect' with Placido indices. From the moment the corneas are labeled as "suspicious", they need to reconsider the indication of corneal refractive surgery. In this context, the problem is rather to check that this suspicion is based, and not driven by excess (false positivity for indices, whose specificity is not absolute).
Eyes that have been included in our model are similar to those that pose a diagnostic problem in the check prior to refractive surgery, like the one shown here:
The risk of ectasia eyes present some minor, but located anomalies within the limits of conventional topographic detection)4). The use of a clinical model based on the study of the eye the least reached in the case of a very asymmetrical breach between the eyes was used or taken over by many authors)5-8). Due to the scarcity of the apparently unilateral forms of Keratoconus)2,3), the formation of enough with eyes in some way of a form fruste of Keratoconus (negative for tests in force while their contralateral eyes are achieved) represents a certain difficulty: it took us almost 10 years to collect a large enough sample.
Using a discriminant function
Corneas "Normal Placido" but belonging to a patient genetically Keratoconus (reached proven of the contralateral eye) have been studied in topography of elevation by scanning by light slots (Orbscan IIz, Technolas PV, Germany), and compared to a control group of healthy corneas belonging to some myopic patients operated of LASIK have reported no complications during the 5 years of postoperative follow-up.
In these eyes with Keratoconus frustes forms, many indices calculated from the elevation anterior, posterior and the product were statistically different from those measured at eyes normal)1). The irregularity of curvature of the anterior face calculated in the Central 3 mm was also statistically increased (0.98 + / 0.34 vs 1.25+/-0.38 D). However, the comparison of distributions between two samples (corneas normal vs. form fruste of Keratoconus) reveals a significant overlap in the distributions of these values.
It is interesting to note that despite the normality of indices Placido, a statistical test that is performed between the Group of affected corneas of Keratoconus fruste and normal corneas reveals a statistically significant difference in anterior curvature. The normality of the indices Placido simply means that the values taken by the indices calculated for each of these corneas are below the thresholds initially chosen for these tests! In absolute terms, the irregularity of the anterior face of the affected fruste Keratoconus corneas remains statistically more important than those of the normal corneas averaged: However, the superposition of the values taken by the corneas of each sample does not bode of obtaining a good sensitivity and specificity with a test based solely on that criterion, and a threshold is set lower. One could certainly identify shapes frustes of Keratoconus with this simple test and a lowered threshold, but they accuse of many normal eyes wrongly...
Other parameters were statistically significant differences between the two groups: Central average thickness was reduced (524.3 +/-35 vs 554.6 +/-36 microns), the difference between this value and the end point (point windows) was increased (12.1 +/-5.6 vs 6.8+/-3.1 microns), the distance with the geometric center of the fine was increased (0.95 + / 0.37 vs 0.64 +/-0.32) , and the elevation value later with respect to the sphere of reference calculated after centering on the thinnest point was greater next to this point (26.3 + / 11 microns vs 19.7+/-8.6 microns).
As noted previously, the averages calculated for each of these parameters, although significantly different statistically, were too close to the distribution of the measured values to enable them, considered in isolation, be really clinically significant, and can build a sufficiently sensitive and specific screening test. Yet, the gradient of thinning of the cornea from the periphery of the cornea to the Center, the index of irregularity topographic to 3 mm, the shift of the vertical of the end point, the difference between the Central Product and the finest product as well as the difference between the lower keratometry average and the higher average keratometry measured 5 mm from the vertex are among the clues showed a potential discriminatory power. However, using isolated from each index does not differentiate with sufficient sensitivity and specificity the normal corneas of the corneas of the group studied due to the overlap important values made by the sampled corneas.
On the other hand, thecombined use of these criteriabased on the calculation of a composite index with a technique ofdiscriminant analysisled to a more sensitive and specific diagnostic test. The control group used to build the test consisted of eyes of myopic patients aged under 50, made of myopic LASIK without complication (especially the ectasia), and followed for 5 years at least. Remember that the study group was composed of classified as normal eyes with a topography of Placido and neural network based on the use of indices Klyce and Maeda: these eyes are however likely to evolve spontaneously (and especially in a case of corneal surgery) form of ectasia. The choice of an optimal threshold led to a sensitivity of 93% and a specificity of 92% for the screening of Keratoconus fruste.
These results were responsible for the design of thealgorithm of the SCORE Analyzer (SCORE: 'Screening Corneal Objective Risk of Ectasia') based on the use of a combination of specular topographic indices of Placido and elevation with some power discriminant (existence of a statistically significant difference in the averages calculated between the groups tested for each of these indices). Among the clues with a statistically significant difference between the two groups, to have been selected Twelve of the most discriminating. Each of these indices was used and contributed to the calculation of a score, with a discriminant function that combined linearly.
The score allows you to sort comments according to the degree of similarity with likely corneas of spontaneous ectasia (evolution towards a more pronounced form of Keratoconus). The threshold chosen, which corresponds to the border to separate the samples studied, with maximum specificity and sensitivity has been adjusted to take the value 'zero '.
A positive score (> 0) predicted a suspicious cornea, while a negative score (< 0) predicted a normal cornea. The value of the score is positive, more the topographical characteristics of the cornea under review are close to those of Keratoconus, and vice versa. The realization of corneal refractive surgery must be reconsidered in case of positive, even weakly negative value depending on the clinical context (strong myopic correction, atopic, etc.)
Examples of SCORE software
Here is an example of map obtained from an Orbscan acquisition in a patient with a very asymmetrical form of Keratoconus (the left eye had a proven form).
The next case is a case of ectasia iatrogenic post LASIK, where the SCORE software could be used retrospectively and measure a positive Score in preoperative.
The preoperative maps, which aroused no particular suspicion, were retrospectively used to establish a map with the SCORE Analyzer software.
The Score of the right eye is positive, indicating that the combination of topographical indices allowed to come to a conclusion that the subjective inspection could easily guess: the presence of a susceptibility for the corneal ectasia.
The score of the left eye (no complicated evolution) was slightly negative:
Interest of SCORE software
The interest of an automated system of topographic subclinical Keratoconus detection novice is multiple. It allows all first to combine a set of discriminating clues from the specular topography, elevation and thickness in a single digit (the score), for a more comprehensive assessment of each studied cornea. It's the first automated detection method that combines clues of topographies Placido, elevation and pachymetrique, and this association has proven its superiority to the separate use one or the other of the two technologies)9–,11).
Corneal topography is a reference tool for the detection of Keratoconus subclinical forms. Specular Placido topography allows to track some of these forms (forms labeled as suspicious Placido) subclinical, but its sensitivity and specificity are not sufficient to abstain from the collection of data of the elevation and the total product (tomography).
All these results converge and strongly suggest that the surgeon concerned to increase the sensitivity of detection of subclinical Keratoconus beginner must pay attention to the review of the posterior side of the cornea and its thickness, which is evaluated more comprehensively by an examination of the distribution pachymetrique (tomography map or product). SCORE Analyzer is designed to achieve this goal.
VIDEO: introduction to the SCORE software analyze (Bordeaux, 24 may 2014)
see the article linked on a study to validate the SCORE Analyzer: https://www.gatinel.com/2013/10/saad-gatinel-d-retrospective-testing-of-the-score-for-the-detection-of-ectasia-susceptibility-casee-report-of-ectasia-7-years-after-lasik-int-j-kerat-ect-cor-dis20132273-78/
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