Page 118 - Feline diagnostic imaging

116 7 Normal Cross-sectional Anatomy of the Eye and Orbit

Ciliary Sclera
body Choroid

Posterior Retina
chamber

Cornea

Lens Optic nerve
Vitreous
Anterior
chamber

Extraocular
muscle
Iris

Anterior Posterior
lens capsule lens capsule

Figure 7.5 Schematic illustration of the normal anatomic features of the eye of a cat.

posterior lens capsule, and retina‐choroid‐sclera interface junction (limbus) is defined by the transition between the
(Figures 7.7 and 7.8). The anechoic structures (aqueous lowly reflective cornea and highly reflective sclera due to
humor, lenticular cortex, vitreous cavity) are represented the more irregular collagen distribution of the sclera
by the flat baseline [7,13,31]. (Figure 7.10) [12,35].

7.1.4.2 Anterior Chamber
7.1.4 Anterior Segment
The anterior chamber is delineated by the cornea, iris, and
The ocular anterior segment is composed by cornea, cor- anterior lens capsule [12]. The anterior chamber appears as
neo‐scleral limbus, anterior chamber, iris, irido‐corneal an anechoic black area on B‐mode [10]. Anterior chamber
angle (ICA), ciliary body, lens, and posterior chamber as depth (ACD) is easily measured using UBM from the inter-
depicted in Figure 7.9. Unique features of the feline ante- nal corneal surface to the lens surface (Figure 7.11) [35].
rior segment include a relatively wide ICA and deep ante- The ACD described in cats is 4.2 mm (range 3.6–4.66 mm)
rior chamber [23]. UBM quantitative measurements of and compared to the human, dog and pig, the cat has a
anterior segments dimension have been performed in enu- relatively deep anterior chamber [23]. The posterior cham-
cleated cat eyes [23]. ber communicates with the anterior chamber through the
pupil. Using high‐resolution transducers, the posterior
7.1.4.1 Cornea chamber can be seen as an anechoic, triangular space
Depending on the probe frequency, the cornea presents as a between the lens, ciliary body, and iris (Figure 7.9) [4,35].
single or double parallel echogenic line [10,29]. Using a
high‐resolution probe, the cornea appears as two discrete, 7.1.4.3 Lens
parallel echogenic lines representing the anterior epithelial The normal lens appears as a very well‐outlined, oval ane-
layer and the posterior endothelium‐Descemet membrane choic structure on B‐scan and exhibits very low internal
separated by an anechoic (low reflective) corneal stroma reflectivity on A‐scan [29]. The lens is represented by con-
(Figure 7.10). Axial corneal thickness described in cats vex and concave curvilinear echoes that correspond to the
measured by UBM is 0.74 mm [4,7,23,35]. The corneoscleral anterior and posterior lens capsule, respectively [31]. The