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S.V. Quisling, K. Goins, J. Sutphin; Pentacam Analysis of Keratoconus Indices in Normal Patients . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1360.
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Topographic criteria for the diagnosis of Keratoconus are controversial. Pattern recognition by an experienced observer is sensitive in detecting abnormalities, but there remains a need for an automated detection program. The newest version of the Oculus Pentacam contains software with a keratoconus classification system based on indices that are compared to mean values and standard deviations of a normal population.
Retrospective analysis of keratoconus indices and keratoconus classification of pre–operative Pentacam topography obtained on 29 normal patients subsequently had uncomplicated lasik surgery from 4/04 to 10/05. The scans were prior to the installation of the keratoconus software and not included in the pre–operative evaluation. The topography was re–examined with respect to the keratoconus indices. For 36 Pentacam scans, the mean for the keratoconus indices used by Pentacam for keratoconus classification and specificity for the keratoconus classification system were calculated.
Twenty–two percent of the normal pre–operative scans had KK1 classification, 3% scans had KK1–2 classification. Specificity of the test was calculated to be 75% based on less than KK2 classification, but was 100% for KK3. Index of surface variance had a mean value of 27.89 with 3% having an abnormal index (>37) and 3% having a pathological index (>41). For the keratoconus Index, the mean value was 1.03 with 25% with abnormal index (>1.07). For the Radii minimum, the mean value was 7.15 with 3% having an abnormal index (<6.71).
The value of these systems or classifications has yet to be determined. From this data on "normal" patients, we can say that the Pentacam software for keratoconus classification specificity of 75% based on less than KK2 classification, but was 100% for KK3. The low specificity will lead to many false–positive results and further evaluation of the criteria will be necessary in order to use this system in the screening of keratoconus especially in presumed normal patients to avoid over diagnosing forme fruste keratoconus.
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