Double-Pass Retina Point Imaging for the Evaluation of Optical Light Scatter, Retinal Image Quality, and Staging of Keratoconus

PURPOSE: To measure retinal image quality using point spread function (PSF) analysis by double-pass retina point imaging in patients with keratoconus and to correlate visual quality with disease severity. METHODS: Patients diagnosed as having keratoconus by clinical examination, topography, and tomography and normal eyes were included in this study. A commercially available double-pass retina point imaging instrument (OQAS 108 II AcuTarget HD; Visiometrics S.L., Terrassa, Spain) was used to collect Objective Scatter Index (OSI) values in 21 keratoconic and 22 normal eyes. Eyes were also subjected to corneal topography and tomography, and staged using the Keratoconus Severity Score (KSS) and Amsler-Krumeich (AK) scales. RESULTS: The OSI was increased in keratoconic eyes (5.85 +/- 0.98) versus control eyes (0.83 +/- 0.12; mean +/- SEM), in AK stages 1 to 4, and KSS stages 3 and 4. Receiver-operator characteristic analysis obtained an area under the curve (AUC) of 0.859 when evaluating the OSI as a unimodal diagnostic indicator for any KSS stage and 0.993 for KSS stages 3 and higher. An AUC of 0.949 was obtained in comparing eyes with lower severity topographic aberrations (KSS 1 and 2) versus mild to moderate keratoconus (KSS 3 and 4). Increasing corneal steepening patterns on tomography and topography were associated with PSF broadening and increased OSI. CONCLUSIONS: Double-pass retina point imaging is useful in correlating retinal image quality with keratoconus severity. The OSI may represent a clinically significant parameter for staging keratoconus with a unique ability to directly evaluate quality of vision in this population.