Forme Fruste Keratoconus Imaging and Validation via Novel Multi-Spot Reflection Topography
We present the case of a 45-year-old male subject diagnosed with topographic and topometric asymmetrically manifested FFKC [, ] between his two eyes. The patient, a resident of Sweden, father of a 17-year-old adolescent who had developed keratoconus, attended treatment with the Athens Protocol procedure of his son in our institution []. Due to the known hereditary nature of the disease [], our keratoconus protocol involves examination of next-of-kin whenever possible.\nThree imaging modalities were studied in this work. Scheimpflug imaging was provided by the WaveLight Oculyzer II (Alcon Surgical, Fort Worth, Tex., USA), a Pentacam HR (high-resolution) camera providing corneal pachymetry and tomography imaging (covering a 9-mm diameter area). The system, running on Examination Software version 1.17r47, additionally provides keratometry, topographic keratoconus classification and computes irregularity keratoconus indices, namely the Index of Surface Variance (ISV) and the Index of Height Decentration (IHD) [, ]. Placido imaging was provided by the WaveLight Allegro Topolyzer (Alcon Surgical). The Topolyzer is a wide cone Placido system covering an approximately 8.5 mm-diameter area with 22 concentric rings for the detection of up to 22,000 elevation points. Both systems are incorporated in our keratoconus screening protocol and are employed in the topography-guided treatment in conjunction with accelerated cross-linking [].\nThe Cassini (running on software version 1.1.1) was employed to provide anterior surface imaging. The system produces anterior elevation, tangential and axial curvature, and refractive power three-dimensional maps covering approximately a 7.5-mm diameter area. The report provides keratometry data (steep and flat K, simulated astigmatism), and computes topographic and keratoconus indices, namely the Surface Asymmetry Index (SAI) and the Surface Regularity Index (SRI) []. In addition, an aberrations report is provided, according to the Zernike nomenclature. Four consecutive scans in each case were obtained by all systems.\nThe right eye (OD), the more symptomatic to the patient, had uncorrected distance visual acuity of 20/25 and manifest refraction of plano +0.50 × 45°. Corrected distance visual acuity with this prescription was 20/20. In addition to the complete ocular examination, the FFKC diagnosis was further confirmed by Scheimpflug topometry and Placido topography. Data supporting this diagnosis include thinnest local corneal thickness of 492 μm, and an asymmetric posterior surface elevation, indicating a minimum depression of −31 μm located superiorly and a maximum protrusion of +25 μm located inferiorly. However, this eye (as well as the less affected OS) was classified as nonkeratoconic according to the Scheimpflug imaging-provided topographic keratoconus classification. []\nThe left eye (OS), the less affected, had uncorrected distance visual acuity of 20/20 and manifest refraction of plano. The rather symmetric posterior elevation, as obtained by the Pentacam, indicated a minimum superior depression of −25 μm, minimum inferior depression of −17 μm, and a maximum local inferior protrusion (within the center 2-mm area) of +13 μm. The thinnest local corneal thickness was 496 μm.\nRepeatability results for flat and steep keratometry, astigmatism and meridian axis as measured by all three modalities, were assessed by the standard deviation of data from the four consecutive acquisitions. Descriptive statistics for the above parameters are reported in table . Results from the Cassini keratoconus indices (SAI and SRI) and Scheimplug-derived keratoconus indices (ISV and IHD) [] are reported in table . Results from anterior elevation data as measured by the Cassini and the Pentacam are reported in table .\nComparative examples of anterior elevation maps from both modalities employed in the study for the more affected OD and the less affected OS eye are provided in fig. , b, respectively. In addition, comparative examples of anterior surface curvature maps for the evidently asymmetric OD and the less affected OS are provided in fig. , respectively. Fig. presents the results of the Placido topography system imaging for the right (top) and left (bottom) eye.\nThis study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of our Institution. Informed consent was obtained from the subject at the time of the first clinical visit.