Eye anatomy images

At the time the article was last revised Craig Hacking had the following disclosures: • Philips Australia, Paid speaker at Philips Spectral CT events (ongoing) • Taylor and Francis Publishing, Paid author of Imaging for Students 5th edition (ongoing) These were assessed during peer review and were determined to not be relevant to the changes that were made. Article: • • • • • • • • • • • • Images: • Gross anatomy Location The globe is suspended by the Size Each globe is an approximately spherical structure with relatively constant size in adults with normal eyesight, and does change with age nor does it varies with sex 2,10. A normal adult emmetropic eye measures (by CT, sclera to sclera) 10: • ~24.2 ± 2 mm (transverse, horizontal) • ~23.7 ± 2 mm (sagittal, vertical) • ~23.5 ± 2 mm (axial, anteroposterior) Importantly, both myopia and hypermetropia can change the axial diameter substantially: down to ~20 mm in hypermetropia and up to ~26 mm in myopia 10. Structure The surface of the globe is made up of three layers, the outermost fibrous layer, the intermediate vascular layer, and the innermost neural layer. This trilaminar structure brings about a further subdivision of the eye into two major segments; the anterior segment, which contains aqueous humor, and the posterior segment, which contains the gel-like vitreous humor. Both of these substances allow diffusion of nutrients to adjacent structures and act to maintain the shape of the globe. The fundus of the globe refers...

The iris—the circular, colored area of the eye that surrounds the pupil—controls the amount of light that enters the eye. The iris allows more light into the eye (enlarging or dilating the pupil) when the environment is dark and allows less light into the eye (shrinking or constricting the pupil) when the environment is bright. Thus, the pupil dilates and constricts like the aperture of a camera lens as the amount of light in the immediate surroundings changes. The size of the pupil is controlled by the action of the pupillary sphincter muscle and dilator muscle. The retina contains the cells that sense light (photoreceptors) and the blood vessels that nourish them. The most sensitive part of the retina is a small area called the macula, which has millions of tightly packed photoreceptors (the type called cones). The high density of cones in the macula makes the visual image detailed, just as a high-resolution digital camera has more megapixels. The front section ( anterior segment) extends from the inside of the cornea to the front surface of the lens. It is filled with a fluid called the aqueous humor, which nourishes the internal structures. The anterior segment is divided into two chambers. The front (anterior) chamber extends from the cornea to the iris. The back (posterior) chamber extends from the iris to the lens. Normally, the aqueous humor is produced in the posterior chamber, flows slowly through the pupil into the anterior chamber, and then drains out of the ey...

When we look at an object, light reflected from it enters the eye and is refracted, or bent. This creates a focused, upside-down image of the object that the brain will have to interpret and turn in the correct direction. Inside the eye are photoreceptors, which create nerve impulses when struck by light. There are two types: cones make color vision possible, and rods specialize in black-and-white images. Although our eyes can only see in two dimensions, we are able to determine distances and depth in our three-dimensional world. This is because the brain interprets the two slightly different images our left and right eyes see as one. This is called stereoscopic vision. Other visual cues, such as shadows, how objects are blocking each other, and our knowledge about the sizes of different objects also help us determine depth and distance. A series of muscles helps the eye move. The first set is the superior and inferior rectus muscles, which allow upward and downward motion. The medial and lateral rectus muscles allow the eye to move from side to side while staying level. The superior and inferior oblique muscles let it move up or down and to the side. Most of these muscles are controlled by the oculomotor nerve. Friction from these movements would quickly damage the eye without lubrication. Tears released by the lacrimal gland are spread around by blinking, and provide lubrication for the eye. Tears also help remove foreign objects and bacteria that could cause damage. Las...