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Structure & Function of the Human Eye

The human eye is similar to the structure of a camera. All parts of the eye must function together properly to produce clear vision. The function of the eye is to convert light into an electrical signal which is then transmitted to the brain through the optic nerve. It is in the brain that this electrical signal is converted into vision. To illustrate this, we will follow the path light takes as it travels through the eye and discuss the various ocular structures encountered. Light from the outside world passes through various layers of the eye. Come with us on an “illuminating” journey along this path of light:


The first surface encountered by a ray of light is the tear film. The eye’s surface must be kept moist at all times. To achieve this, glands in and near the eyelids produce both tears and a special oil which mix together and coat the eye. This tear film coats the cornea which normally is the crystal clear window to the eye. Behind the cornea, we enter a space called the anterior chamber which is filled with fluid called the aqueous. The aqueous is normally clear like water and is responsible for maintaining the pressure of the eye.


Inside the anterior chamber is the iris. This is the part of the eye which is responsible for one’s eye color. It acts like the diaphragm of a camera, dilating and constricting the pupil to allow more or less light into the eye.


The next structure we encounter is the crystalline lens. The lens is responsible for focusing light onto the retina. It changes shape slightly to allow us to change focus between objects that are near and those that are far.


Next in our voyage through the eye is the vitreous. This is a jelly-like substance that fills the body of the eye. It is normally transparent.


Finally, light reaches the retina, a thin tissue lining the innermost wall of the eye. The retina acts much like the film in a camera. The retina senses light rays hitting it and converts them to electrical signals carried by the optic nerve to the brain. The peripheral parts of the retina are responsible for side to side while the central area, called the macula, is used for reading vision and color vision. The very center of the macula is called the fovea. It has a very high concentration of special cells called cones which make it the only part of the retina capable of perfect or 20/20 (6/6) vision.

Optic Nerve

The optic nerve is the structure which takes the information from the retina as electrical signals and delivers it to the brain where this information is interpreted as a visual image.

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