Abstract
Purpose: The purpose of this study was to establish a novel bilateral differential topographic algorithm and assess its efficacy for screening of keratoconus and corneal ectasia before corneal refractive surgery. Methods: One hundred and sixty-one consecutive patients (115 men and 46 women, aged 22.8 ± 6.8 years) with keratoconus, including clinical keratoconus, subclinical keratoconus, forme fruste keratoconus (FFK), and corneal ectasia (KC group) and one hundred and seventy-four consecutive patients (97 men and 77 women, aged 25.1 ± 6.7 years) with ametropia (control group) visiting the Eye and ENT hospital of Fudan University from June 2018 to April 2021 were included. Bilateral differential keratometry, elevation, and pachymetry topographies were composed based on raw topographic data obtained by a Scheimpflug imaging anterior segment analyzer. Key bilateral differential characteristic parameters were calculated. SPSS 20 (SPSS Inc., IBM) was used for statistical analyses and the receiver operating characteristic (ROC) curves were used to determine the diagnostic efficacies. Results: Mann-Whitney tests detected that the front keratometry, front elevation, corneal pachymetry, and back elevation maximal, mean, and standard deviation values within a 1.5-mm radius of the bilateral differential topography were all significantly higher in the KC group than in the control group (all p-values <0.001). The front keratometry mean (ΔFKmean) and standard deviation (ΔFKsd) and the front elevation standard deviation (ΔFEsd) and maximal (ΔFEmax) values within a 1.5-mm radius of the bilateral differential topography yielded the four highest accuracies (area under the ROC curve = 0.985, 0.985, 0.984, and 0.983, respectively) for discriminating KC cases (including FFK cases) from normal cases. Cut-off values of 0.75 diopters (D) for the ΔFKmean, 0.67 D for the ΔFKsd, 2.9 μm for the ΔFEsd, and 14.6 μm for the ΔFEmax had the highest sensitivities (95.7, 95.0, 96.9, and 95.0%, respectively) and specificities (96.0, 97.7, 94.8, and 95.4%, respectively). Conclusion: Bilateral differential topographic parameters may be efficient for the early detection of keratoconus and corneal ectasia secondary to corneal refractive surgery. This bilateral differential topographic algorithm may complement conventional diagnostic models by improving the sensitivity and specificity of screening for early keratoconus and ectasia before corneal refractive surgeries.
Highlights
Keratoconus and ectatic diseases are characterized by an abnormal thinning and conic protrusion of the cornea that could result in significant visual impairment
By rotating 180° in less than 3 s, the camera was capable of capturing more than 60 tomographic images with 230,400 data points to form a front keratometry matrix (FKM), back keratometry matrix (BKM), front elevation matrix (FEM), back elevation matrix (BEM), corneal pachymetry matrix (CPM), iris matrix, and crystalline lens matrix, reconstructing a three-dimensional anterior segment model
Mann–Whitney tests revealed that the ΔFKmax, ΔFKmean, ΔFKsd, ΔFEmax, ΔFEmean, ΔFEsd, ΔCPmax, ΔCPmean, ΔCPsd, ΔBEmax, ΔBEmean, and ΔBEsd values of the KC group were significantly higher than those of the control group (Table 2)
Summary
Keratoconus and ectatic diseases are characterized by an abnormal thinning and conic protrusion of the cornea that could result in significant visual impairment. Common risk factors for keratoconus include family history, ocular allergy, constant eye rubbing, as well as connective tissue disorders. These diseases often go undetected initially, and they tend to progress from one eye to the other, with a prevalence of approximately 1/2000 in the general population (Gomes et al, 2015a; Gomes et al, 2015b; Naderan et al, 2017). Amsler introduced the Amsler–Krumeich diagnostic and classification system to assess the severity of keratoconus based on the mean corneal power, astigmatism, transparency, and corneal thickness (Amsler, 1946). Though this system improved the accuracy of diagnosing keratoconus, demonstrating a sensitivity of 89.3% and specificity of 71.9% (Gobbe and Guillon, 2005; Saad and Gatinel, 2016), its accuracy was still too low for screening keratoconus prior to corneal refractive surgery
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