Nanotechnology applications in ophthalmology

The human eye is a complex, highly specialized body organ. It is the sensory organ for vision that contains the light-sensitive retina and the refractive system that focuses light onto the retina. It is connected to the central nervous system through the optic nerve that carries the visual information to higher visual centers that allows us to see. Although a thorough discussion of the eye anatomy and physiology is beyond the scope of this review, appreciating some of the basic anatomy and physiology is important in understanding the applications of nanotechnology in the field of ophthalmology. The eye anatomy can be simplified by describing the eye as a sphere with a diameter of approximately 23 mm, with its wall consisting of three layers (Figure 3.1). The outer layer consists of the transparent cornea anteriorly and the white sclera posteriorly. The middle layer (called uvea) is highly vascular and consists of the iris and the ciliary body anteriorly and choroid posteriorly. The innermost layer, the retina, contains the light-sensitive photoreceptors (rods and cones), intermediate neurons (bipolar and amacrine cells), and the retinal ganglion cells (RGCs) whose axons form the optic nerve. The inside of the eye contains the lens and is filled by the gel-like vitreous (posteriorly) and the aqueous humor (anteriorly).