Superiority of Baseline Biomechanical Properties over Corneal Tomography in Predicting Keratoconus Progression

ABCD progression display for keratoconus progression: a sensitivity-specificity study

OBJECTIVE

To evaluate the sensitivity and specificity of the ABCD progression display for keratoconus progression.

METHODS

Data was collected from patients that underwent at least two Pentacam assessments 6 months apart. Sensitivity and specificity were calculated for the ABCD progression display. Progression was defined by criterion 1: change in two ABCD parameters above 80% confidence interval (CI) or criterion 2: change in one ABCD parameter above 95%CI. Receiver operating characteristic analysis compared the area under the curve (AUC) of all ABCD parameter combinations.

RESULTS

Thirty eyes were evaluated over a median time of 10.3 months. Progression by criterion 1 resulted in a sensitivity of 61.9% and specificity of 88.9%. Progression by criterion 2 resulted in higher sensitivity (80.9%) and specificity (100%). Pairwise comparisons of the ROC curves show that the AUC achieved by criterion 2 was significantly higher than criterion 1 (0.905 vs. 0.754, p = 0.0332). Evaluation of all ABCD combinations with a significant change of 80% or 95% CI did not show superiority over criterion 1 or 2 regarding progression detection. The D parameter had a very low AUC (0.5-0.556).

CONCLUSIONS

The ABCD progression display can assess keratoconus progression with high sensitivity and specificity, thus assisting the patients' decision-making process. The D parameter did not contribute to the sensitivity or specificity of this classification.

Refractive and Topographic Parameters of the Belin/Ambrósio Module in Patients with Refractive Defects in Cuenca, Ecuador

Objective:

This study aimed to describe the refractive and topographic parameters of the Belin/Ambrósio module in patients with refractive defects at the Latino clinic in Cuenca, Ecuador, between 2017 to 2021.

Methods:

A descriptive, cross-sectional study was carried out. A database included anonymous cases of patients with refractive defects treated at the ophthalmological consultation of a Latino clinic from January, 2017 to June, 2021 was searched. Data was collected using a form containing study variables. Microsoft Excel and SPSS were used for data collection and analysis using frequencies, percentages, and measures of central tendency.

Results:

The sample consisted of 120 patients; 61.7% were women, and 38.3% were men. Moreover, 70.8% of patients were young adults. The pachymetry mean of the center of the pupil, apex, and position of lowest pachymetry was 521 µm, 520 µm, and 513 µm, respectively. The means of the flattest keratometry, curviest keratometry, and maximum keratometry were 43.30 D, 46.32 D, and 48.01 D, respectively.

Conclusion:

Cases distribution according to anterior and posterior elevation showed pathological values ​​in more than 50% of the studied corneas. According to the average progression index, pathological elevation was found in 18.8% of the cases, and according to the average deviations, 25.4% presented corneal ectasia in different stages.

Corneal Biomechanics - an Emerging Ocular Property with a Significant Impact

Corneal biomechanical properties reflect the capacity of the cornea to respond to applied mechanical forces. They are an increasingly important domain in ocular pathology, correlated to the diagnosis and evolution of eye diseases such as refractive errors, glaucoma or corneal ectasias. Refractive errors constitute a significant etiology of decreased vision worldwide, with a particular impact in children. Myopic eyes significantly differ from emmetropic eyes in terms of morphology and biomechanics, with differences being reported in both adults and children. In the latter, corneal hysteresis (CH) and the corneal resistance factor (CRF) are significantly lower in myopic individuals, and both biomechanical parameters correlate with the central corneal thickness and axial length. Glaucoma is a progressive optic neuropathy that leads to thinning of the nerve fiber layer and specific visual field loss, in which intraocular pressure (IOP) is an important risk factor. There is an inverse correlation between IOP and CH - a low hysteresis is associated with a high IOP. Furthermore, CH is on average lower in primary open angle glaucoma (POAG) compared to ocular hypertension (OHT) for the same IOP. Significant correlations between CH and the thickness of the ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL), in both POAG and OHT, have been described. Keratoconus is the most frequent corneal ectasia, which leads to a progressive thinning and protruding of the cornea. Biomechanical parameters are severely affected in keratoconus - usually, both CH and CRF are lower compared to normal eyes. The biomechanical behavior of the cornea modulates the evolution of several ocular pathologies. As research is ongoing, more data will enable us to apply this knowledge in diagnosing disease more efficiently and targeting the right treatment for the right patient, including refractive surgery.