Special Senses

Body Systems

Intro to Health Occupations

By: Michaela Sebastiani


Ophthalmology deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems. Since ophthalmologists perform operations on eyes, they are both surgical and medical specialists.

The Eye

The eye is the optical system which gets light from the environment, adjusts it through the diaphragm, focuses it through the changeable lenses to make an image, modifies this image into a set of electrical signals, and sends these signals to the brain through the neural pathways that connect the eye to the optic nerve to the striate cortex and other areas of the brain.


The eye is protected well.

  • The eyelid and eyelashes protect the eye from dust and other irritants.
  • The bony socket around the eye, the orbit, protects the eye from injury.
  • The tear ducts, lacrimal glands, makes tears which flow over the eye and into canals that take irritants and debris away.

The Eye has Three Layers

Other Special Structures

  • The Pupil- The pupil is the opening in the center of the iris. The size of the pupil determines the amount of light that enters the eye. The pupil size is controlled by the dilator and sphincter muscles of the iris.
  • The Lens- a biconvex structure and is suspended behind the colored iris. Both are behind the protective cornea.
  • The Aqueous Humor- a transparent, gelatinous fluid similar to plasma, but containing low protein concentrations. It is located in between the lens and the cornea.
  • The Vitreous Humor- the clear gel that fills the space between the lens and the retina of the eyeball.

Connective Tissue

The iris, visible through the cornea, is composed of connective tissue and muscle with a hole in the middle. The color of the iris is actually due to the amount of pigment in the iris connective tissue layer. Brown eyes have a lot of pigment, blue eyes very little.


"Refraction is the anomoly which makes images possible by the eye. Most of that refraction in the eye takes place at the first surface, since the transition from the air into the cornea is the largest change in index of refraction which the light experiences. About 80% of the refraction occurs in the cornea and about 20% in the inner crystalline lens. While the inner lens is the smaller portion of the refraction, it is the total source of the ability to accommodate the focus of the eye for the viewing of close objects. For the normal eye, the inner lens can change the total focal length of the eye by 7-8%" Refraction and the Eye.


Accommodation is the process in which the vertebrate eye changes focusing power to keep a clear image or focus on an object as its distance varies.


Amblyopia is an eye disorder that distinguishes by an impaired vision in an eye that otherwise appears normal, or irregular to associated deformities of the eye. Amblyopia is also known as "lazy eye".

A Journey Through the Human Eye: How We See


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