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8

Diseases of the Eye
Eva M. Abarca

Hospital Ars Veterinaria, Barcelona, Spain

Ocular ultrasound (US), computed tomography (CT), and keratopathy [12,20,25]. Corneal sequestrum describes a
magnetic resonance imaging (MRI) are excellent cross‐ feline corneal disorder characterized by an area of cor -
sectional diagnostic methods that enable determination of neal degeneration with amber to black discoloration par-
the location and extent of diseases affecting the ocular and ticularly prevalent in Persian and Himalayan breeds
orbital tissues in cats [1–9]. Ocular ultrasound has become [26–28]. The majority of the sequestra are located in the
the most important diagnostic tool for the evaluation of superficial stroma but extension to the midstroma or
ocular pathology, especially with opaque ocular media, and Descemet membrane is not uncommon [27]. Typically,
is indicated also for the evaluation of ocular tumors and for opacification involving the anterior portion of the cornea
biometry [10–17]. obscures direct clinical determination of the full extent and
Detailed knowledge of the normal ultrasonographic depth to which the lesion involves the cornea [20,27,29–31].
anatomy of the eye and retrobulbar space is essential to fur- High‐resolution ultrasound and UBM are valuable adjuncts
ther identify and characterize ocular and orbital pathology in the evaluation of corneal sequestrum in the cat and
(see Chapter 7, normal eye and orbit). As soon as a lesion is facilitate the planning of surgical management of corneal
detected, topographic echography (location, extension, disease [10,20,32]. The UBM appearance has been
shape), quantitative (reflectivity, internal structure, sound described as a highly reflective structure invading the cor-
attenuation) and kinetic echography (after‐movement, vas- neal stroma surrounded by an area of low echogenicity
cularity) are advised to provide a means of differentiating consistent with corneal necrosis (Figure 8.3) [10,20].
intraocular lesions (Figures 8.1 and 8.2) [15,18]. Crystalline keratopathies associated with stromal depos-
As reviewed in Chapter 7, the ocular anterior segment is its of lipid or calcium are rare in cats although they have
composed of the cornea, corneo‐scleral limbus, anterior been described following chronic corneal ulceration and
chamber (AC), iris, irido‐corneal angle (ICA), ciliary body, inflammation [27,33–35]. Both lipid and calcium clinically
lens, and posterior chamber. Conventional ultrasound appear as superficial stromal opacities that resemble
(10 MHz) is not well suited for anterior segment evaluation ground glass [27]. Using UBM, these lesions are character-
[4,11,14,19]. As a result, high‐resolution ultrasound and ized by the presence of a hyperechoic well‐defined lesion
ultrasound biomicroscopy (UBM) have been developed to located in the anterior stroma (Figure 8.4).
allow specialized examination of the anterior segment
[20–24].
8.2 Inflammatory and Neoplastic
Diseases Affecting the Anterior Segment
8.1 Cornea
Anterior uveitis, iris, or ciliary body tumors and uveal
Congenital and acquired ocular diseases in cats that cysts are common ocular abnormalities in cats [35].
affect the cornea include keratitis, crystalline keratopa- Differentiating between these entities is critical for visual
thies, neoplasia, trauma, corneal sequestrum, and bullous and survival outcome in the feline patient.

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.