The Eye: Anatomy, Physiology, and Pathology
In a number of ways, the human eye works much like a camera:
1. Light is focused primarily by the cornea — the clear front surface of the eye, which acts
like a camera lens.
2. The iris of the eye functions like the diaphragm of a camera or microscope, controlling
the amount of light reaching the back of the eye by automatically adjusting the size of the
pupil.
3. The eye's crystalline lens is located directly behind the pupil and further focuses light.
Through a process called accommodation, this lens helps the eye automatically focus on
near and approaching objects.
4. Light focused by the cornea and lens (and limited by the iris and pupil) then reaches the
retina — the light-sensitive inner lining of the back of the eye. The retina converts optical
images into electronic signals. The optic nerve then transmits these signals to the visual
cortex — the part of the brain that controls our sense of sight.
Common Ocular Disorders
Myopia. Inability to focus on distant objects. Eyeball is too long. Most common reason for glasses.
Presbyopia. This is the loss of the ability to clearly see close objects or small print. It is a normal process
that happens slowly over a lifetime, but you may not notice any change until after age 40. Presbyopia is
often corrected with reading glasses.
Floaters. These are tiny spots or specks that float across the field of vision. Most people notice them in
well-lit rooms or outdoors on a bright day. Floaters often are normal, but can sometimes indicate a more
serious eye problem. Retinal detachment may be heralded by showers of floaters accompanied by light
flashes.
Dry eyes. This happens when tear glands cannot make enough tears or produce poor quality tears. Dry
eyes can be uncomfortable, causing itching, burning, or rarely some loss of vision. Using a humidifier may
help, or “artificial tears”, or plugs that are placed in tear ducts to decrease tear drainage.
Tearing. Having too many tears can come from being sensitive to light, wind, or temperature changes.
Protecting your eyes by shielding them or wearing sunglasses can sometimes solve the problem. Tearing
may also indicate a more serious problem, such as an eye infection or a blocked tear duct.
Cataracts. Cataracts are opacifications or cloudy areas within the lens of the eye. Since the lens in a
healthy eye is clear, light has no problem passing through the lens to the back of the eye to the retina
where images are processed. When a cataract is present, the light cannot get through the lens as easily
and, as a result, vision can be impaired. Cataracts often form slowly, causing no pain, redness, or tearing
in the eye. Some stay small and do not alter eyesight. If they become large or thick, cataracts can usually
be removed by surgery.
Glaucoma. This condition occurs when there is a progressive deterioration of the optic nerve. Glaucoma
is usually associated with an increased pressure of the eye. The eye is like a tire that generally has a
normal and safe pressure. When this pressure is increased, it can be associated with damage to the optic
nerve; this is called primary open angle glaucoma.
Retinal disorders. The retina is a thin lining on the back of the eye made up of cells that collect visual
images and pass them on to the brain. Retinal disorders interrupt this transfer of images. They include
age-related macular degeneration, diabetic retinopathy, and retinal detachment. Early diagnosis and
prompt treatment of these conditions is critical if vision is to be maintained.Continue reading
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Conjunctivitis. This is a condition in which the tissue that lines the eyelids and covers the cornea
becomes inflamed. It is sometimes called "pink eye". It can cause redness, itching, burning, tearing,
discharge, or a feeling of something in the eye. Conjunctivitis occurs in people of all ages and can be
caused by viral or bacterial infection, allergies, or exposure to chemicals and irritants.
Corneal diseases. The cornea is the clear, dome-shaped "window" at the front of the eye. It helps to
focus light that enters the eye. Disease, infection, injury, and exposure to toxic agents can damage the
cornea causing eye redness, watery eyes, pain, reduced vision, or a halo effect. Treatments include
making adjustments to the eyeglass prescription, using medicated eye drops, or having surgery.
Subconjunctival Hemorrhage. This is a ruptured blood vessel over white of the eye: “blood shot eye”.
It is a relatively common condition. It is painless and benign. It always resolves within a few days.
