Characteristics of Corneal Astigmatism of Anterior and Posterior Surface in a Normal Control Group and Patients With Keratoconus

The ABCD Keratoconus Grading System-A Useful Tool to Estimate Keratoconus Progression in the Pediatric Population

PURPOSE

To evaluate the ABCD grading system in pediatric keratoconus.

METHODS

A retrospective cohort analysis of all children with keratoconus followed up at the Shamir medical center between 2010 and 2017. A recommendation by the treating physician to undergo corneal crosslinking (CXL) was used as an estimate for clinically significant disease progression. The ABCD grading was not available to the treating physician and was computed post hoc. The ABCD grading was compared between patients who required CXL with those who did not. A single eye of each patient was included.

RESULTS

Fifty eyes of 50 children were analyzed. The mean age at presentation was 15.56 ± 1.36 years. In 23 eyes, progression of keratoconus was recorded and CXL was performed (CXL-group). On presentation, the stable and CXL groups did not differ significantly in their clinical parameters. In the CXL-group, a statistically significant increase was seen in the ABCD staging (P < 0.001). In the stable group, the ABCD staging did not change significantly in parallel visits (P = 0.87). An increase of 1 point in the sum of the ABCD staging showed a 5-fold risk for undergoing CXL (odds ratio = 5.28; 95% CI, 1.82-15.34). There was no significant change in the Amsler-Krumeich classification in the CXL group.

CONCLUSIONS

Among a cohort of pediatric patients with keratoconus, worsening in the ABCD grading was associated with disease progression, whereas no significant change was demonstrated in the Amsler-Krumeich classification The ABCD grading system is a useful tool for initial assessment of disease progression in the pediatric population, in which early recognition is of paramount importance.

Site of clear corneal incision in cataract surgery and its effects on surgically induced astigmatism

Clear corneal incision (CCI) is a commonly used surgical approach in cataract surgery. In this prospective study, we evaluated the effect of CCI site on surgically induced astigmatism (SIA) and other postoperative astigmatic changes. CCIs were constructed based on the steep meridian of the total corneal refractive power in the 4.0-mm-zone (TCRP_4.0), and patients were divided into four groups: temporal, superotemporal, superonasal, and superior according to the site of the incision. TCRP_4.0 analysis demonstrated a statistically significant reduction of astigmatism with superior incisions (P < 0.001), and the combined mean polar values for SIA changed significantly in the temporal (Hotelling T² = 1.977), superotemporal (Hotelling T² = 0.544), superonsal (Hotelling T² = 1.066), and superior incision groups (Hotelling T² = 1.134) (all P < 0.001). The posterior axis alignment should be considered in cataract surgery with CCI, and the SIA is affected by axis rotation, and incision orientation.

Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes

Purpose:

To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.

Methods:

A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.

Results:

The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.

Conclusion:

Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.