The authors used microscopy and synchrotron-based small-angle X-ray scattering analysis (SAXS) to describe lesions macroscopically typical of tropical keratopathy (“Florida spots”) from 6 cats on St Kitts. Microscopically, there were varying degrees of epithelial hyperplasia and thinning of the cornea (by 4% to 18%) due to loss of corneal stroma associated with dense accumulations of collagen in the superficial stroma. The collagen fibrils in lesions were wider and had more variable diameters (39.5 ± 5.0 nm, mean ± SD) than in normal corneas (25.9 ± 3.6 nm; P <.01). There were occasional vacuoles (<1 μm) in the corneal epithelial basement membrane but no evidence of inflammation, edema, stromal neovascularization, fibrosis, acid-fast organisms, or structures suggestive of a fungal organism. SAXS analysis showed collagen fibril diameters and variation in size were greater in stroma containing the lesions compared to normal corneas (48.8 ± 4.5 nm vs 35.5 ± 2.6; P <.05). The d-spacing of collagen in the stroma of lesions and normal corneas was the same, but the average orientation index of collagen in lesions was greater (0.428 ± 0.08 vs 0.285 ± 0.03; P <.05). A survey revealed Florida spots lesions were static over time and became less obvious in only 1 of 6 affected cats adopted on St Kitts and taken to areas in the US where lesions are not reported. An anterior stromal collagen disorder with various degrees of epithelial hyperplasia is the pathologic hallmark of lesions clinically identical to Florida spots in cats from St Kitts.
Bibliographical noteFunding Information:
Part of this research was undertaken on the SAXS/WAXS beamline at the Australian Synchrotron, part of the Australian Nuclear Science and Technology Organization (ANSTO). We thank Jordan Taylor of the Manawatu Microscopy Centre. We are also grateful to Dr Fernanda Castillo Alcala from the Institute of Veterinary, Animal and Biomedical Science at Massey University and to Dr Teri Weronko and Dr Andrea Peda from Ross University Veterinary Clinic; and David Hilchie, histology lab manager, Ross University School of Veterinary Medicine, for technical support and assistance with sourcing samples. The author(s) received the following financial support for the research, authorship, and/or publication of this article: The Australian Synchrotron paid for travel and accommodation for the SAXS measurements.
- Florida spots
- collagen disorder
- corneal opacity
- punctate keratopathy