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Pentacam Scheimpflug Tomography Findings in Topographically Normal Patients and Subclinical Keratoconus Cases
Pentacam Scheimpflug Tomography Findings in Topographically Normal Patients and Subclinical Keratoconus Cases EDITOR: ˜ OR WE READ WITH INTEREST THE ARTICLE BY RUISEN
Va´zquez and associates, which reported that detectable back corneal surface abnormalities do not necessarily arise before anterior changes.1 However, there is another opinion that we would like to express. We believe that posterior corneal surface elevation is a sensitive index for the early diagnosis of keratoconus. Keratoconus often occurs in the central or paracentral cornea. Elevation of posterior corneal regions near the pupil has great diagnostic value.2,3 We think that elevation of the posterior corneal surface is more valuable for describing the corneal surface abnormalities of subclinical keratoconus than the back corneal surface deviation index, and that elevations of different regions of the posterior cornea have distinct clinical values. Posterior corneal elevation is better than anterior corneal elevation for discriminating subclinical keratoconus from normal corneas. Therefore, we feel that it is necessary to evaluate the diagnostic value of posterior corneal elevation in the central or paracentral cornea for keratoconus, rather than analyze the elevation of the entire posterior corneal surface. In other words, if the authors compared the sensitivity of anterior and back corneal surface elevations rather than the front corneal surface deviation index (Df) and back corneal surface deviation index (Db), they might derive conclusions that differ from those presented in this article. In conclusion, this article showed the efficacy of posterior corneal parameters for identifying corneas with subclinical keratoconus. However, posterior corneal surface elevation is a sensitive parameter for the diagnosis of subclinical keratoconus and is superior to anterior corneal elevation. YAN JIA HAOBIN ZHU JIBO ZHOU
Shanghai, China THE AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. The authors indicate funding support from the National Nature Science Foundation of China, Foundation Number 81371050.
REFERENCES
1. Ruisen˜or Va´zquez PR, Galletti JD, Minguez N, et al. Pentacam Scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases. Am J Ophthalmol 2014;58(1):32–40.e2.
VOL. 159, NO. 1
2. de Sanctis U, Aragno V, Dalmasso P, Brusasco L, Grignolo F. Diagnosis of subclinical keratoconus using posterior elevation measured with 2 different methods. Cornea 2013;32(7): 911–915. 3. de Sanctis U, Loiacono C, Richiardi L, Turco D, Mutani B, Grignolo FM. Sensitivity and specificity of posterior corneal elevation measured by Pentacam in discriminating keratoconus/ subclinical keratoconus. Ophthalmology 2008;115(9):1534–1549.
REPLY WE APPRECIATE THE COMMENTS FROM JIA AND ASSOCIATES
regarding our statement on the diagnostic value of anterior and posterior corneal elevation relative to each other. We must emphasize that our study was not meant to explore this specific aspect of keratoconus detection, but our data did in fact suggest what the authors questioned. In order to better support this claim, we went back to our dataset, which unfortunately only included front and back elevation at the thinnest corneal location, as provided by the Pentacam’s Belin-Ambro´sio display. The thinnest point is usually within the ‘‘corneal region near the pupil,’’ as the authors suggest, although the latter is somewhat complicated to define. For discriminating between Groups 1 and 2 (see the original article for details1), the area under the receiver operating characteristic curve for front elevation was 0.90 6 0.03, whereas for back elevation it was 0.91 6 0.03. The optimal cutoff value (defined as that closest to the perfect classification point in the curve) was >5 mm for front elevation (78% sensitivity, 94% specificity) and >10 mm for back elevation (82% sensitivity, 91% specificity). When comparing Groups 1 and 3, the area under the curve for front and back elevation was the same, 0.97 6 0.02, and the optimal cutoff values were >6 mm for front elevation (95% sensitivity, 96% specificity) and >17 mm for back elevation (95% sensitivity, 100% specificity). But when dealing with subclinical keratoconic eyes (fellow eyes with unremarkable topography), the area under the curve for front and back elevation was 0.85 6 0.04 and 0.86 6 0.04, respectively; and the optimal cutoff values were >4 mm (73% sensitivity, 83% specificity) and >8 mm (76% sensitivity, 86% specificity), respectively. After the additional analysis, we believe that the argument in question still holds; that is, that back elevation data do not seem to be clinically superior to front elevation for keratoconus detection. This statement on posterior elevation was suggested earlier by de Sanctis and associates,2 who concluded that ‘‘its efficacy is lower for subclinical keratoconus, and thus data concerning posterior elevation should be combined with curvature data in stratifying patients with this condition.’’ Nonetheless, we must acknowledge that neither our study nor that of de Sanctis and associates was designed to determine whether detectable back corneal changes occur before front abnormalities,
CORRESPONDENCE
209
Va´zquez and associates, which reported that detectable back corneal surface abnormalities do not necessarily arise before anterior changes.1 However, there is another opinion that we would like to express. We believe that posterior corneal surface elevation is a sensitive index for the early diagnosis of keratoconus. Keratoconus often occurs in the central or paracentral cornea. Elevation of posterior corneal regions near the pupil has great diagnostic value.2,3 We think that elevation of the posterior corneal surface is more valuable for describing the corneal surface abnormalities of subclinical keratoconus than the back corneal surface deviation index, and that elevations of different regions of the posterior cornea have distinct clinical values. Posterior corneal elevation is better than anterior corneal elevation for discriminating subclinical keratoconus from normal corneas. Therefore, we feel that it is necessary to evaluate the diagnostic value of posterior corneal elevation in the central or paracentral cornea for keratoconus, rather than analyze the elevation of the entire posterior corneal surface. In other words, if the authors compared the sensitivity of anterior and back corneal surface elevations rather than the front corneal surface deviation index (Df) and back corneal surface deviation index (Db), they might derive conclusions that differ from those presented in this article. In conclusion, this article showed the efficacy of posterior corneal parameters for identifying corneas with subclinical keratoconus. However, posterior corneal surface elevation is a sensitive parameter for the diagnosis of subclinical keratoconus and is superior to anterior corneal elevation. YAN JIA HAOBIN ZHU JIBO ZHOU
Shanghai, China THE AUTHORS HAVE COMPLETED AND SUBMITTED THE ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. The authors indicate funding support from the National Nature Science Foundation of China, Foundation Number 81371050.
REFERENCES
1. Ruisen˜or Va´zquez PR, Galletti JD, Minguez N, et al. Pentacam Scheimpflug tomography findings in topographically normal patients and subclinical keratoconus cases. Am J Ophthalmol 2014;58(1):32–40.e2.
VOL. 159, NO. 1
2. de Sanctis U, Aragno V, Dalmasso P, Brusasco L, Grignolo F. Diagnosis of subclinical keratoconus using posterior elevation measured with 2 different methods. Cornea 2013;32(7): 911–915. 3. de Sanctis U, Loiacono C, Richiardi L, Turco D, Mutani B, Grignolo FM. Sensitivity and specificity of posterior corneal elevation measured by Pentacam in discriminating keratoconus/ subclinical keratoconus. Ophthalmology 2008;115(9):1534–1549.
REPLY WE APPRECIATE THE COMMENTS FROM JIA AND ASSOCIATES
regarding our statement on the diagnostic value of anterior and posterior corneal elevation relative to each other. We must emphasize that our study was not meant to explore this specific aspect of keratoconus detection, but our data did in fact suggest what the authors questioned. In order to better support this claim, we went back to our dataset, which unfortunately only included front and back elevation at the thinnest corneal location, as provided by the Pentacam’s Belin-Ambro´sio display. The thinnest point is usually within the ‘‘corneal region near the pupil,’’ as the authors suggest, although the latter is somewhat complicated to define. For discriminating between Groups 1 and 2 (see the original article for details1), the area under the receiver operating characteristic curve for front elevation was 0.90 6 0.03, whereas for back elevation it was 0.91 6 0.03. The optimal cutoff value (defined as that closest to the perfect classification point in the curve) was >5 mm for front elevation (78% sensitivity, 94% specificity) and >10 mm for back elevation (82% sensitivity, 91% specificity). When comparing Groups 1 and 3, the area under the curve for front and back elevation was the same, 0.97 6 0.02, and the optimal cutoff values were >6 mm for front elevation (95% sensitivity, 96% specificity) and >17 mm for back elevation (95% sensitivity, 100% specificity). But when dealing with subclinical keratoconic eyes (fellow eyes with unremarkable topography), the area under the curve for front and back elevation was 0.85 6 0.04 and 0.86 6 0.04, respectively; and the optimal cutoff values were >4 mm (73% sensitivity, 83% specificity) and >8 mm (76% sensitivity, 86% specificity), respectively. After the additional analysis, we believe that the argument in question still holds; that is, that back elevation data do not seem to be clinically superior to front elevation for keratoconus detection. This statement on posterior elevation was suggested earlier by de Sanctis and associates,2 who concluded that ‘‘its efficacy is lower for subclinical keratoconus, and thus data concerning posterior elevation should be combined with curvature data in stratifying patients with this condition.’’ Nonetheless, we must acknowledge that neither our study nor that of de Sanctis and associates was designed to determine whether detectable back corneal changes occur before front abnormalities,
CORRESPONDENCE
209