Prediction of total corneal power in keratoconus using anterior surface data.

CLINICAL RELEVANCE: Keratoconus results in an increase in anterior and posterior curvatures and a reduction in corneal thickness. Anterior corneal ectasia is partially compensated by remodelling the corneal epithelium. Therefore, there is an alteration in the relationship between corneal surfaces and variation in corneal power. The variation in corneal power is one of the sources that induces errors in IOL power calculation. BACKGROUND: This study aimed to assess a method for predicting total corneal power in keratoconus using several anterior surface parameters at 3 mm and 4 mm. METHODS: Tomographic data obtained using Pentacam (Oculus, Germany) were analysed from 280 eyes of 140 patients with keratoconus using anterior and posterior keratometry, anterior Q-value at 8 mm, central corneal thickness, Kmax location and value, and true net power at 4 mm (TNP). Calculated total corneal power (TCPc) at 3 mm was obtained using the Gauss formula. Predicted total corneal power at 3 mm (TCPp3) and 4 mm (TCPp4) was obtained from univariate (TCPp3u and TCPp4u) and multivariate linear regression formulae (TCPp3m and TCPp4m). SimK, anterior Q-value, vertical location, and Kmax value were used in the multivariate formulae. Mean absolute error (MAE) and median absolute error (MedAE) were also calculated. Absolute frequencies within dioptric ranges of all formulas divided for keratoconus grading were evaluated. RESULTS: TCPc and TNP exhibited a good correlation (R2 = 0.58, p < 0.05) with a higher dispersion above 50 D of corneal power. Highly significant correlations were observed between TCPp3u and TCPc (R2 = 0.978, p < 0.05) and TCPp3m and TCPc (R2 = 0.989, p < 0.05). Lower but significant correlations were observed between TCPp4u and TNP (R2 = 0.692, p < 0.05) and between TCPp4m and TNP (R2 = 0.887, p < 0.05). The best results for TCP prediction at 3 and 4 mm were obtained with TCPp3m and TCPp4m as follows: MAE of TCPp3m was 0.24 ± 0.20 (SD) D with MedAE of 0.20 D, while MAE of TCPp4m was 0.96 ± 0.77 D with MedAE of 0.80 D. The 3 mm multivariate regression formula results in higher absolute frequencies of prediction errors in the total eyes within 0.5 D (93%) than the univariate formula (81%). At 4mm, the multivariate regression formula has a lower percentage within 0.5 D (32%) than the univariate formula (41%), but the percentage of the multivariate formula is higher within 1 D (63%) than the univariate formula (56%). CONCLUSION: All formulas show a decrease in accuracy with increasing grades of keratoconus. Multivariate linear regression formulae using only anterior surface data can predict TCP with good approximation in eyes with keratoconus in cases where posterior surface parameters are unavailable. The vertical location of Kmax and the anterior asphericity could play a relevant role in the prediction of total corneal power in keratoconus.

Comparison between IOL MASTER 500 and MYAH with vector analysis in low and mild anterior corneal astigmatism.

PURPOSE: Evaluate the agreement between IOL Master 500 (Carl Zeiss Meditec AG, Germany) and MYAH (Topcon EU, Visia Imaging, Japan) in measuring axial length, keratometry, and anterior corneal astigmatism. SETTING: Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Ophthalmology Clinic, University of Messina, Messina, Italy. METHODS: In this prospective study, 40 eyes (right eye 25, left eye 15) of 40 patients were included. Axial length (AL), keratometry (K1, K2), and anterior corneal astigmatism (ACA) were measured. AL, mean K (Kavg) and magnitude of ACA were compared using Bland - Altman plot analysis, parametric and nonparametric statistical analysis. The difference vector and angle of error of the ACA measured by the two devices were evaluated by vector analysis using polar diagrams. RESULTS: Mean and standard deviation with IOL Master and with MYAH device was for AL 24.25 ± 1.22 mm and 24.25 ± 1.22 mm (p = .99), for Kavg 42.75 ± 1.53 D and 42.85 ± 1.52 D (p = .78), for Magnitude of ACA 1.00 ± 0.58 D and 0.89 ± 0.56 D (p = .38) respectively. High correlations were found for AL (R² = 0.999), Kavg (R² = 0.996), and ACA Magnitude (R² = 0.889). Bland-Altman analysis of the two devices found high agreement and absence of proportional bias (MYAH-IOL MASTER) were found between the two assessments for AL (bias = -0.0005 mm, p = .93), Kavg (bias = 0.0955 D, p = .76) and ACA (bias = 0.11 D, p = .41). Limit of agreement (upper/lower LoA, 95%CI) were respectively +0.057/-0.058 mm for AL, + 0.29/-0.09 D for Kavg and +0.49/-0.27 D for ACA. No statistical difference was found between the x-component and y-component of the ACA vector (p > .01), the difference vector (IOL MASTER-MYAH) was +0.14 D axis 159 with an absolute mean angle of error of 7.2 ± 7.5 degree. CONCLUSIONS: The instruments appear to be interchangeable for measurements of AL, keratometry, and magnitude of ACA with high agreement between the two devices. Also, in the presence of low astigmatism, the two instruments give the same results in terms of ACA.

The Role of Hi-Tech Devices in Assessment of Corneal Healing in Patients with Neurotrophic Keratopathy.

To prove the role of high-tech investigation in monitoring corneal morphological changes in patients with neurotrophic keratopathy (NK) using Keratograph 5M (K5M) and anterior segment OCT (AS-OCT), corneal healing was monitored with Keratograph 5M (Oculus, Wetzlar, Germany) and AS-OCT (DRI, Triton, Topcon, Tokyo, Japan) in 13 patients (8F and 5M), aged from 24 to 93 years (67.8 ± 19) with severe NK, who were treated with Cenegermin 0.002% (20 µg/mL) (Oxervate®, Dompè, Farmaceutici Spa, Milan, Italy). The surface defects were evaluated on Keratograph 5M with ImageJ software and the corneal thickness variations were measured using DRI-Triton OCT software. Instrumental procedures were performed at baseline, and after 4 and 8 weeks of the treatment, respectively. The main outcome measures were reduction of the ulcers' area and corneal thickness recovery. The mean area of the corneal ulcers was reduced between baseline and 4 weeks examination in all patients, and at 8 weeks all ulcers were completely healed. An increase of the corneal thickness was evidenced between the baseline visit and after the 4- and 8-week follow-up, respectively. Additionally, only in collaborating subjects the In Vivo Confocal Microscopy (IVCM) was performed with HRT Rostock Cornea Module (Heidelberg Eng GmbH) to study the corneal nerves fibres. High-tech diagnostics with K5M, AS-OCT and IVCM proved useful in the assessment of corneal morphology and the healing process in patients with NK and could be extended to assess other corneal pathologies.