Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 57

The vitreous humor is a transparent hydrogel that comprises a portion of the clear ocular media and accounts for up to two‐thirds of globe volume. Anteriorly, the vitreous provides support for the lens as it rests in a shallow concavity (i.e., the patella fossa), while posteriorly, the vitreous abuts the neurosensory retina. As a result, the vitreous functions to transmit light, to maintain the shape of the eye, and to help maintain the normal position of the lens and retina.

Embryologically, the vitreous is composed of three components: (i) primary vitreous (containing the hyaloid artery system); (ii) secondary (definitive, or adult) vitreous; and (iii) tertiary vitreous (lens zonules) (Figure 1.51). The primary, or primitive, vitreous develops first, as the hyaloid artery system courses through it to provide a blood supply to the avascular developing lens. The secondary vitreous then forms around the primary vitreous, leaving the primary vitreous at the central core of the vitreal compartment. The secondary vitreous becomes the definitive, or adult, vitreous. Within the adult vitreous exist several anatomical structures, potential spaces, and connection points between the vitreous and adjacent tissues. The core of the primary vitreous around which the adult vitreous develops is occupied by Cloquet's canal (i.e., the hyaloid canal), and the remnant of the anterior insertion of the hyaloid artery appears as a dense, white, small dot (i.e., Mittendorf's dot) with a variable “corkscrew” tail extending from the posterior pole of the lens.

Figure 1.51 Schematic illustrating the various components of and spaces within the vitreous. The secondary, or adult, vitreous is composed of the cortical and central (intermediate zone) components. Asterisk denotes not a true “membrane.”