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Frank S. Hwang, Arusha Gupta, Kraig S. Bower, Albert S. Jun; Variability In Pentacam Measurements In Paitients With Keratoconus. Invest. Ophthalmol. Vis. Sci. 2012;53(14):124.
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Keratoconus is the most common corneal dystrophy characterized by progressive, non-inflammatory corneal thinning that result in corneal protrusion, irregular astigmatism, and decreased vision. Pentacam (Oculus, Inc., Wetzlar, Germany) is Scheimpflug camera based system utilized for three dimensional imaging of the anterior segment of the eye in a non-contact method without requiring topical anesthesia. Reliability and reproducibility of Pentacam in normal eyes has been previously studied by several different groups and these studies showed good interobserver and intraobserver reliablity. However, there has not been many studies looking at reliablity of Pentacam acquired corneal parameters for patients with keratoconus.
This is a prospective case study. Patients with known or new diagnosis of keratoconus who came for their regular follow up at Wilmer was recruited. The disease is usually monitored by obtaining a Pentacam image at their clinic visits. After oral consent, Pentacam imaging was performed three times (one minute apart). Patients with known or new diagnosis of Keratoconus and normal volunteers between the age of 18-70 was included in the study. Patients with other co-existing corneal disorders which may change the topography was excluded from the study. We then compared the keratometric, pachymetric, and fixation values of the three tests to determine the variability of these parameters within each group. Patients were divided in 3 groups based on topographic astigmatism: ≤3 diopters, >3 diopters but ≤6 diopters, and >6 diopters.
The study enrolled 35 keratoconus patients (60 eyes) and 10 controls (20 eyes). Analysis of the keratoconus group showed that the mean variability of keratometric, pachymetric and fixation values were statistically significant for > 6 diopters of topographic astigmatism group compared to the two other keratoconus group and normal controls (p <0.05 using 2 tailed t-test). In addition, the mean variability of keratometric, pachymetric and fixation values of the control group compared to all three keratoconus group were statistically significant (p <0.05 using 2 tailed t-test).
There are several factors that may contribute to unreliability of Pentacam imaging in patients with keratoconus. The patient’s visual acuity may be decreased due to corneal scarring or significant astigmatism. Depending on the severity of their disease process, these patients may have difficulty fixating on the fixation target during image acquisition of the Pentacam imaging system to produce unreliable alignment and measurements.
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