In humans the retina is the innermost layer of the eye, which consists of retinal pigment epithelium (RPE) and neural retina. The neural retina has several layers and various cell types, which are illustrated in Figure 1. RPE is a single layer of hexagonal cells that maintains the homeostasis of neural retina. It has essential biochemical, physiological, physical, and optical functions in maintaining the visual system, including phagocytosis of rod outer segments, transport of substances between photoreceptors and choriocapil-laries, and uptake and conversion of the retinoids, which are needed in visual cycle. Together with endothelial cell linings of retinal capillaries, RPE forms the blood-retinal barrier. The neural retina is a complicated and delicate multilayer. The thickness of neural retina varies from 0.4 mm near the optic nerve to about 0.1 mm anteriorly at the ora serrata. The photoreceptors are the light-sensing part of retina. The electric impulses are amplified and integrated by bipolar, horizontal, amacrine, and ganglion cells. The principal glial cell of the retina is the Muller cell. The bipolar cells ir Ganglion cell layer

Fig. 1 Light photomicrograph of a rat retinal section. The inner nuclear layer includes the nuclei of bipolar, amacrine, horizontal, and Müller cells. The nuclei of rods and cones are in the outer nuclear layer.

Inner nuclear layer

Outer nuclear layer

Outer segment of photoreceptors

Retinal pigment epithelium

Fig. 1 Light photomicrograph of a rat retinal section. The inner nuclear layer includes the nuclei of bipolar, amacrine, horizontal, and Müller cells. The nuclei of rods and cones are in the outer nuclear layer.

are the first and ganglion cells the second neuron of the visual pathway from photoreceptors to brain. Macula is the central part of retina located temporally of optic nerve head between the upper and lower temporal vessels. Fovea is the central, approximately 1.5 mm wide sloping part of macula. Visual acuity is decreased quickly in the paramacular areas. Of the photoreceptors, the cones take care of photoptic and color vision and are located mainly in the macula. Rods are the main photoreceptor type in the periphery; they are specialized to scotopic vision.

The human retina may be affected by many vascular diseases such as occlusions, vasculitis, and anomalies. Retinopathy of prematurity (ROP) is a retinal disease affecting premature children, where the growth of developing retinal vasculature is interrupted. Diabetic retinopathy is a common cause of blindness, while arteriosclerosis, hypertension, and other cardiovascular diseases may cause changes in the retinal vasculature. Neovascularization is also associated in macular degeneration.

In retinal detachment, fluid is collected in the potential space between the neural retina and RPE. In rhegmatogenous detachment, the fluid comes from the vitreous cavity through a retinal hole or tear. Extravasation may originate from choroid or retina and results in secondary retinal detachment. Retinal detachment caused by the traction of fibrous bands in vitreous is called traction retinal detachment. Traumas, intraocular inflammations, retinal or vitreal degeneration, or vitreal bleeding are etiological factors of retinal detachment. Proliferative vitreoretinopathy (PVR) is found in about 5% of retinal detachments. It is characterized by the formation of vitreal, epiretinal, or subretinal membranes after retinal reattachment surgery or ocular trauma. In some cases the membranes cause traction and distortion of retina. Severe postoperative PVR is the most common cause of failed retinal detachment surgery.

Retinoblastoma is a malignant retinal tumor with an incidence of about 1: 20,000. The genetic abnormality of this disease located to 13q14. Both genes in this locus must be abnormal before this malignancy develops. In the nonhereditary form, mutation occurs only in the retinal cells. In the hereditary form the patient has inherited the first mutation from his or her parents, and 90% of these patients develop a clinical retinoblastoma.

In this chapter we present some recent development in the retinal disease models of animals. Models of retinal degeneration, proliferative diseases, and neovascularization are presented. These models are important tools in current research, since various growth factors, gene therapies, and transplantation strategies have demonstrated possibilities for treating severe retinal diseases.

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