The Retina and Prosthetic Devices

The retina is the innermost layer of the eye. It is basically composed of two layers, the outer retinal pigment epithelium (RPE) and the inner neural (sensory) retina

Figure 2.1

Sagittal section of an adult human eye (from Ogden, 1989; modified by Kolb, 2001).

Figure 2.1

Sagittal section of an adult human eye (from Ogden, 1989; modified by Kolb, 2001).

(figure 2.1). The sensory retina is a delicate sheet of transparent tissue varying in thickness from 0.4 to 0.15 mm. The anatomical site for detailed fine vision, called the fovea, is in the center of the macula. The outermost layer of the sensory retina consists of photoreceptors (figure 2.2); in the macular region, the photoreceptors are mostly cones (color-sensitive). Other more inner layers of the sensory retina are the inner nuclear layer with bipolar, amacrine, and horizontal cells; and the ganglion cell layer. The axons of the ganglion cells form the optic nerve after traversing the nerve fiber layer.

Photoreceptor loss from diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are the leading cause of legal blindness. Despite near-total loss of photoreceptors in these diseases, there is relative preservation of the other retinal neurons. By stimulating the remaining functional retinal layers, it may be possible to restore visual perception. In other diseases, this approach may not be practical. For example, in glaucoma (high intraocular pressure with optic nerve damage), the ganglion cells are primarily damaged. In diseases such as retinopathy of prematurity, diabetic retinopathy, and vascular diseases of the retina, all the layers are affected. In these diseases, it is highly unlikely that electrical stimulation of the retina can restore visual function, and other approaches such as retinal transplantation or electrical stimulation of the visual cortex should be investigated.

Was this article helpful?

0 0

Post a comment