Tropical Keratopathy (Florida Spots) in Cats

Abstract

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.

Disseminated idiopathic lipid keratopathy in a normolipemic cat

“…This cat was evaluated in the same manner as other patients with corneal deposits, beginning with slit‐lamp examination and general laboratory tests, and then with further corneal OCT scan. This workup allows for the evaluation of other possible etiologies such as tropical keratopathy (“Florida spots”), and infectious crystalline keratopathy 16,17 . Although these two diagnoses were considered, the absence of an inciting event for tropical keratopathy, such as travel to a tropical area or fire ant exposure, along with a lack of distinctive lesions, allowed for exclusion of this etiology.…”

“…This workup allows for the evaluation of other possible etiologies such as tropical keratopathy ("Florida spots"), and infectious crystalline keratopathy. 16,17 Although these two diagnoses were considered, the absence of an inciting event for tropical keratopathy, such as travel to a tropical area or fire ant exposure, along with a lack of distinctive lesions, allowed for exclusion of this etiology. The lesions present in tropical keratopathy are also white or cream-colored, but they usually have blurry cotton-like contours, unlike the welldefined lesions present in this feline patient.…”

Birefringence analysis of collagen supraorganization in cat corneas with tropical keratopathy

“…A previous study 28 conducted in St. Kitts involving six domestic short‐haired cats demonstrated that tropical keratopathy is associated with alterations in the diameter and alignment of collagen fibers. The changes were detected by comparing the collagen supraorganization in the lesions to those in a control group, which included adjacent transparent corneal tissue and tissue samples collected from two clinically normal cats.…”

Effects of Preservatives on Corneal Collagen Parameters Measured by Small Angle X-ray Scattering Analysis

“…The technique has been used for the analysis of a wide range of substances, including biological materials where it has been particularly useful in studies of collagen in leather, (5)(6)(7)(8) tendon, (9,10) and the cornea, (11)(12)(13)(14)(15)(16)(17) most recently to characterize a lesion of veterinary importance. (18) The ultrastructure of collagen is often determined by electron microscopy, but to produce the thin tissue sections that are studied, tissues must rst undergo chemical preservation, also called xation. This prevents degradation of tissues by autolysis and putrefaction, stabilizes the ultrastructure, and introduces structural rigidity that facilitates sectioning.…”