CHAPTER 5

The Eyes

Examination of the eyes is always an important part of the physical examination. In addition to detecting the diseases which affect the eyes directly, a doctor can see things in examining the eyes which are signs of the overall health of the body. For example, the eyes can be used to follow the course of such common and potentially dangerous diseases as diabetes and high blood pressure.

First, review the diagram (Figure 5A) of the eye and learn some of the structures which will be discussed below.

1. The Outside of the Eyes:
   The first part of a careful eye examination is inspection of the structures which surround the eye, such as the eyebrows, eyelids, eyelashes and even the holes in the skull (called the orbits) which surround and protect the eye. For the most part, everyone knows what normal eyes look like, but in illness there can be subtle changes which indicate the presence of disease.
   
   There are a number of conditions affecting the appearance of the outer eye:
   
   1. "Black eye" occurs when the soft tissues around the eye, such as the upper and lower eyelid are damaged. Small vessels in these tissues are broken and bleed, causing a brown appearance around the eye.
   2. Sometimes the tiny lining (membrane) which surrounds the eye and protects it can become damaged, and it too can bleed. In this situation, the blood collects between this lining (called the conjunctiva) and the hard white eyeball (called the sclera) and it looks like a red puddle in the white of the eye. Doctors call this sub-conjunctival hemorrhage, because it is bleeding which occurs below the conjunctiva.
   3. When the liver fails to function correctly and get rid of all of the bile which is produced there daily, the whites of the eyes may become yellow/green in appearance, indicating that there is some disease affecting the liver or gall bladder. Some people call this "yellow jaundice". Bile, by the way, is used by the body to help digest fats in the diet.
   4. "Pink eye" occurs when bacteria or viruses invade and infect the hair follicles on the eyelid. Local inflammation occurs, causing pain, swelling, redness and increased temperature of these tissues.
   5. People who have hyperthyroidism (too much of the hormone that speeds up the body's metabolic rate) often have eyes which protrude. Their eyes actually bulge out, making them look as if they are trying to hold their eyes open as wide as possible.
   6. In addition to looking at the eyes, there are times when it is helpful to feel the eyes, and their sockets in order to detect problems. Anyone who has been in an accident, for instance, should have a careful examination of their eye sockets to see if there is any tenderness which could mean a fracture of their skull.
   7. People with complaints of dry or teary eyes should have the tearing system of their eyes examined. There are glands in the upper outer lid above each eye which secrete tears to lubricate the eye's outer lining (conjunctiva). The tears, in the form of a fine layer of fluid, bathe the eye as they flow downward and inward to collecting sacs which are located at the inner lower part of the eyelid of each eye. (Gently pull your lower eyelid down in front of a mirror and see if you can see the small hole where your tears drain.) From there tears drain into the nose, which is why your nose runs when you cry -- when extra tears are draining! To examine whether or not this conducting system is infected, the doctor can press on the sac (located in the lower eyelid nearest the nose) and see that only clear fluid comes out, not colored fluid or pus.

2. The Movements of the Eyes:
   There are several ways in which the eyes move, and each can be compared to the operation of a camera. First, the eyeballs themselves move in order to allow people to look at different things without having to move their heads. This is like moving a camera in order to point at the subject being photographed. Second, the pupils get larger and smaller in order to control the amount of light which enters the back part of the eye. This is similar to the movement of the aperture in the lens of the camera. Finally, the muscles which surround the lens of the eye move, thereby changing the shape of the lens. This allows the person to focus on objects which are at different distances from the eye. In a similar way, the lens of a camera can be manually moved to focus on objects at different distances from the camera.
   
   The movements of each eyeball are controlled by six muscles, which are precisely controlled by special nerves which exit the brain. The movement of the eyes should be tested during the physical examination. The eyes must move in perfect synchrony or the person will see double. This function of the eyes has more to do with the brain than the eye itself, since nerves coming from the brain control the muscles that coordinate these intricate movements.
   
   The eyes are not only designed to move together in complete coordination with each other, but are also designed to move in coordination with the body's movements so that objects can be kept in focus at all times, even when moving. If your eyes were not coordinated in this way, when you walked, everything would be blurred by your movements! When we move, our inner ear senses this movement and tells our brain exactly what type of movement is occurring. The brain then signals the muscles of the eye to move the eyes in such a way as to keep everything that we see in the same place in our visual field, so that it does not appear blurred. You have no doubt heard of handeye coordination -- well, this is ear-eye coordination, and it is much more accurate than hand-eye coordination!
   
   You can illustrate how this works by doing a simple experiment. Hold your hand twelve inches in front of your face and move it back and forth rapidly. Your eyes will not be able to keep up with the movements of your hand and it will appear blurred (That's as good as your hand-eye coordination gets!). Now hold your hand in the same place, and this time move your head side to side rapidly. This time you will notice that you are able to focus on the same place of your hand, and that nothing is blurred. Your inner ear is telling your brain the exact movements of your head, and your brain is then sending the eye signals about how to correct their positions so as to keep everything in sharp focus. Amazing!
   
   A doctor inspecting the eyes will always make sure that the pupils are of equal size and that they react briskly to different intensities of light. This test is easily done by shining a penlight into one eye and watching for the opposite pupil to get smaller. If a person has pupils which are of different sizes it could mean that some part of their nervous system is not functioning properly. If their pupils are very large and do not constrict in response to light, this could indicate brain damage or coma, and if their pupils are very small it could indicate that they have overdosed on certain drugs or medications.
   
   The muscles which change the shape of the lens allow a person to focus on near and far objects at different times. These muscles are rarely involved in diseases, but can sometimes be involved when people have blurred vision and need corrective lenses.

3. The Function of the Eyes:
   Since the function of the eyes is to see objects both far and near, and since we all rely heavily on our sense of sight, any physical examination should always include a test of one's ability to see. The best way to do this test (called a test of visual acuity) is to have someone attempt to read a wall chart at a distance of 20 feet. Each eye is tested separately. In some settings where a wall chart is not available or where there are not 20 feet of space available, a person can be asked to read some small news print of differing sizes to get a crude estimate of the sharpness of their eyesight.
   
   In addition to testing visual acuity it is important to test how well a person can see with their peripheral vision, that is, how well they see the things to either side of them which are not directly in their line of sight. If you are watching television and someone walks into the room to your left or right side you are aware of their presence and motion, even though you are not looking directly at them. This function of your eyes, called peripheral vision, is extremely important. It is important to test this vision because some people can have marked loss in their peripheral vision in advanced diseases of the eye, or other systemic diseases, without even knowing it. Peripheral vision is usually tested by a doctor having you look directly at her or his nose while placing a number of fingers at various positions in your peripheral vision and asking you to cow-it the number of fingers that you see. This is a crude method of testing. Precise testing can be completed by an ophthamologist (eye specialist in medicine) on anyone who demonstrates a deficiency, or has a disease which merits careful and precise peripheral field monitoring.

4. The Inside of the Eye:
   It is important to inspect the inside of the eye for two reasons. First, the retina (lining in the back of the eyeball) is the only place in the body where one can see small arteries, veins and nerves directly. Second, the things which can be seen by a simple eye examination are often important clues to other diseases which affect the whole body, such as high blood pressure and diabetes.
   
   The eye is inspected with the aid of a special light called an ophthalmoscope. [Figure 5B] It is a light with several lenses which allow the doctor to see through the pupil and into the back of the eye where the retina is located. First, the room is darkened to allow the patient's pupils to enlarge so that more can be seen. (If this amount of darkness is not sufficient to allow the pupil to be seen clearly, then special eye drops are placed in the eye to dilate the pupil.) The doctor then asks the patient to focus on a distant object such as a picture on the wall while she or he examines the eye through the ophthalmoscope.
   
   The doctor first sees a reddish reflex coming through the pupil. This shows that the lens is transparent and that light is shining all the way through the fluid-filled eyeball to the back of the eye and onto the retina.
   
   Next, the doctor focuses on the cornea (outer covering of the eye), the iris (muscle which controls the size of the pupil), lens, and finally on the retina (lining in the back of the eyeball). If the eye has been scratched, the cornea can be covered with a special dye which will enable the damage to be seen very clearly. When focusing on the lens it is sometimes observed that the lens may have some imperfections which appear like bubbles in glass. This is usually an early sign of cataract development. Other times, the back of the retina may not be seen with the ophthalmoscope and this too may be an indication of cataract development in the lens. Cataracts occur when the lens of the eye loses part of its transparency, causing partial loss of sight.
   
   Inspecting the retina: The following structures of the retina are usually observed: the vessels, the optic disc and cup, the surface of the retina itself and the macula.
   
   The vessels: As the doctor focuses on the retina, vessels come into view which are the small arteries and veins that supply blood to the retina. The veins usually appear darker and larger than the arteries and can sometimes be seen pulsating. While this is normal in the eye, it is the arteries which pulsate in the rest of the body. The veins are usually larger than the arteries by a ratio of 3:2. If the arteries are much smaller than this it could signal that they are becoming prematurely hardened (a process called arteriolosclerosis which is usually due to high blood pressure).
   
   The optic disc and cup are located at the center of the retina at the back of the eye. This is the location where the optic nerve (the main nerve for vision) comes into the back of the eyeball. It is here that nerves can be seen directly. The disc appears as a circle of reddish-brown color, while the cup is a smaller circle inside the disc which is more yellowish and pink in color.
   
   The cup is the head of the optic nerve. Normally, the cup and disc are round and have distinct, clear margins or edges. The cup should have a diameter less than, or equal to, one third the diameter of the disc. Sometimes the cup may be enlarged beyond this normal amount. This can signal that glaucoma is present.
   
   Glaucoma is a disease of the eye in which pressure builds up in the eyeball, which can eventually cause blindness. This disease often occurs without symptoms, so people don't know that anything is wrong. It is easily diagnosed and treated and since it is a preventable cause of blindness, it is a good reason to have a regular eye exam. An ophthamologist or optometrist can quickly test the pressure in the eye by blowing a puff of air onto the eye. A machine calculates the pressure in the eye based on the resistance that the puff of air encounters. High pressure indicates glaucoma.
   
   The surface of the retina is reddish brown in color and has blood vessels coursing all through it, much like a cobweb spread over a flat surface. Vessels leaking blood or other fluid onto the retina indicate that something is wrong.
   
   The macula is an area at the midline of the retina. To see this area, the doctor asks the patient to look directly into the light coming from the ophthalmoscope. The macula of the retina is usually more dusky appearing and has no vessels crossing it.
   
   Vessels: the condition of the vessels of the retina can serve as indicators of certain diseases. If these vessels are unusually small, for example, this could indicate high blood pressure. If they are more numerous than usual and appear to be forming even more new vessels, this can be a sign that a person has diabetes or that their diabetes is poorly controlled. Sometimes the vessels can break and blood is lost onto the surface of the retina. This can be seen in such diseases as high blood pressure, diabetes, leukemia and also in individuals with severe bleeding disorders.
   
   A POSSIBLE EMERGENCY -- INCREASED PRESSURE IN THE BRAIN:
   Finally, the eye exam can be used as a means of determining something about the pressure in the fluid surrounding the brain. (It is important to know something about the pressure in the brain since abnormally high pressure has many causes, but is almost always dangerous and needs urgent attention.) Since the optic nerve comes into the back of the eye, and since it is surrounded by the fluid which surrounds the brain, changes in the eye can be seen when the pressure of this fluid becomes too high. When the pressure in the fluid surrounding the brain becomes abnormally high, the optic nerve swells and the borders blur (this is called papilledema). As this swelling increases, the veins in the retina often stop their usual pulsating and the optic cup enlarges and bulges into the back of the eye. This can often be seen through the ophthalmoscope.

Chapter 6