Basic Eye Anatomy

Basic Eye Anatomy
Light enters the eye through the cornea, the clear layer covering the front of the eye. The cornea works with the lens of the eye to focus images on the retina. The upper and lower eyelids protect the eye from injury, with the eyelashes forming a protective barrier.

External and Internal Eye Anatomy
The cornea allows light to enter the eye. As light passes through the eye, the iris changes shape by expanding and letting more light through. Or, it constricts and lets less light through to change the size of the pupil. The lens then changes shape to allow the accurate focusing of light on the retina. Photoreceptors in the eye transmit nerve signals through the optic nerve to the brain. The brain processes these nerve impulses into sight.



Lateral Eye Anatomy

The cornea is the clear watch glass covering in the front of the eye. The cornea works with the lens of the eye to focus images on the retina. The retina captures the image and sends it to the brain to be developed. The retina is normally red due to its rich blood supply.

Anatomy of the Eye Lens
The lens is responsible for making sure light rays come to a sharp focus on the retina. The lens of the eye is normally clear. If the lens becomes cloudy or is opacified, it is called a cataract.

Retinoscope

Retinoscope

An eye doctor looks into your eye with a retinoscope.
A retinoscope is used to shine light into a patient's eye for an eye doctor to observe the reflection off the retina. The light is moved back and forth across the pupil. A retinoscope is especially useful in prescribing corrective lenses for patients who are unable to give oral feedback to the eye doctor. It is also useful for determining how well the eyes work together, or accommodate, to see clearly.

Direct Ophthalmoscope

Direct Ophthalmoscope

A direct ophthalmoscope is a hand-held instrument.

A direct ophthalmoscope is a hand-held instrument used for examining the interior structures of the eye, especially the retina. It consists of a mirror that reflects light into the eye and a central hole through which the eye is examined.

Lensometer

Lensometer

A lensometer determines the prescription of a pair of eyeglasses.

A lensometer is an instrument used to measure the power of an existing lens. An optician uses a lensometer to determine the prescription of a patient's eyeglasses.

How the Eye Works

How the Eye Works
Vision is a complex sense composed of many elements. The human eye, elegant in its detail and design, represents a gateway to the process we call vision. The eyeball, or globe, is spherical in shape and about 1 inch across. It houses many structures that work together to facilitate sight.




The human eye is comprised of layers and internal structures, each of which performs distinct functions. The outside layer of the eye is comprised largely of a tough, white, protective tissue called the sclera. The sclera helps maintain the shape of the eyeball. At the front of the eye is an equally tough but clear structure called the cornea, which is responsible for letting light into the eye and bending light.
Going from outside to inside, the next layer of the eye is the choroid, which carries the blood supply necessary to nourish the eye's internal structures. Finally, there is the layer called the retina, lining the inside of the eye, which is sensitive to light and receives stimulation to its specialized cells.
The eye has a number of protective features. The eyelids, eyelashes and eyebrows are all designed to protect the eye from dirt and dust that might enter it and cause damage. The globe sits inside the orbital cavity, a bony pocket lined with fatty tissue as a cushion. Together these provide additional protection against injury. Six muscles attach at various points to the sclera and enable the globe to move in many directions inside the orbit.
In order for vision to take place, a succession of processes must occur involving the structures within the eye and the brain:
The first part of this chain is that light rays must travel through the eye to ultimately focus on the retina. There are a number of structures involved in the bending or refracting of light so that it focuses properly. Light first passes through the clear cornea at the front of the eye, and then through a watery substance called the aqueous humor which fills the small chambers located behind the cornea. As light continues on its pathway it passes through the pupil, a round opening in the center of the iris. The iris is the part of the eye that gives the eye its color. It also is made up of specialized muscles that are able to change the size of the pupil from very small (about 2 mm) to large (about 8 mm), regulating the light that is entering.