Shyam Sunder Tummanapalli1, Vinod Maseedupally2, Preeji Mandathara2, Varsha M Rathi2, Virender S Sangwan2. 1. From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia. Electronic address: shyamsunder@lvpei.org. 2. From the Cornea and Contact Lens Department (Tummanapalli, Mandathara, Rathi, Sangwan), LV Prasad Eye Institute, Hyderabad, India; the School of Optometry and Vision Science (Maseedupally), University of New South Wales, Sydney, Australia.
Abstract
PURPOSE: To determine and compare corneal elevation and thickness indices, thereby formulating a reliable index to distinguish eyes with pellucid marginal degeneration (PMD) from keratoconus eyes and normal (control) eyes. SETTING: LV Prasad Eye Institute, Hyderabad, India. DESIGN: Initial model-building retrospective study. METHODS: Anterior and posterior corneal elevations and thickness indices were obtained from the Orbscan IIz topographer. These values were analyzed and compared between PMD patients, keratoconus patients, and control subjects. RESULTS: Of the indices, the mean values of anterior elevation (AE), ratio of the AE to the anterior best-fit sphere, ratio of the average power values of nasal quadrant to the average power values of inferior quadrant, and difference between maximum keratometry (K) and minimum K were significantly different between the 3 groups (P<.05). The highest area under the receiver-operating-characteristic (AROC) curve in discriminating PMD from keratoconus was for asphericity (0.974; cutoff ≥-0.07; sensitivity 93.3%; specificity 90.6%) followed by the ratio of average power values of the nasal and temporal quadrants to the average power values of the inferior and superior quadrants (Avg NT((D))/IS((D))) (0.959; cutoff ≥1.005; sensitivity 96.7%; specificity 90.6%). The PMD index (AROC curve, 0.935), with a cutoff of 3.45 or higher had 90% sensitivity and 93.7% specificity to distinguish PMD from keratoconus and had 100% sensitivity and 100% specificity to distinguish PMD from control eyes, with a cutoff of 2.46 or higher (AROC curve, 1.000). CONCLUSIONS: The PMD index appeared to be highly sensitive and specific for diagnosing PMD. Asphericity and Avg NT((D))/IS((D)) were clinically relevant in discriminating PMD from other groups.
PURPOSE: To determine and compare corneal elevation and thickness indices, thereby formulating a reliable index to distinguish eyes with pellucid marginal degeneration (PMD) from keratoconus eyes and normal (control) eyes. SETTING: LV Prasad Eye Institute, Hyderabad, India. DESIGN: Initial model-building retrospective study. METHODS: Anterior and posterior corneal elevations and thickness indices were obtained from the Orbscan IIz topographer. These values were analyzed and compared between PMDpatients, keratoconus patients, and control subjects. RESULTS: Of the indices, the mean values of anterior elevation (AE), ratio of the AE to the anterior best-fit sphere, ratio of the average power values of nasal quadrant to the average power values of inferior quadrant, and difference between maximum keratometry (K) and minimum K were significantly different between the 3 groups (P<.05). The highest area under the receiver-operating-characteristic (AROC) curve in discriminating PMD from keratoconus was for asphericity (0.974; cutoff ≥-0.07; sensitivity 93.3%; specificity 90.6%) followed by the ratio of average power values of the nasal and temporal quadrants to the average power values of the inferior and superior quadrants (Avg NT((D))/IS((D))) (0.959; cutoff ≥1.005; sensitivity 96.7%; specificity 90.6%). The PMD index (AROC curve, 0.935), with a cutoff of 3.45 or higher had 90% sensitivity and 93.7% specificity to distinguish PMD from keratoconus and had 100% sensitivity and 100% specificity to distinguish PMD from control eyes, with a cutoff of 2.46 or higher (AROC curve, 1.000). CONCLUSIONS: The PMD index appeared to be highly sensitive and specific for diagnosing PMD. Asphericity and Avg NT((D))/IS((D)) were clinically relevant in discriminating PMD from other groups.
Authors: Dimitrios Karamichos; Paulina Escandon; Brenda Vasini; Sarah E Nicholas; Lyly Van; Deanna H Dang; Rebecca L Cunningham; Kamran M Riaz Journal: Prog Retin Eye Res Date: 2021-11-02 Impact factor: 19.704