The Eye Exam

Assessment of Visual Acuity: The first part of the eye exam is an assessment of acuity. This can be done with either a standard Snellen hanging wall chart read with the patient standing at a distance of 20 feet or a specially designed pocket card (held at 14 inches). Each eye is tested independently (i.e. one is covered while the other is used to read). The patient should be allowed to wear their glasses and the results are referred to as "Best corrected vision." You do not need to assess their ability to read every line on the chart. If they have no complaints, rapidly skip down to the smaller characters. The numbers at the end of the line provide an indication of the patient's acuity compared with normal subjects. The larger the denominator, the worse the acuity. 20/200, for example, means that they can see at 20 feet what a normal individual can at 200 feet (i.e. their vision is pretty lousy). If the patient is unable to read any of the lines, indicative of a big problem if this was a new complaint, a gross estimate of what they are capable of seeing should be determined (e.g. ability to detect light, motion or number of fingers placed in front of them). In general, acuity is only tested when there is a new, specific, visual complaint.

Hand Held Acuity Card

Snellen Chart

Pinhole Testing: The pinhole testing device can determine if a problem with acuity is the result of refractive error (and thus correctable with glasses) or due to another process. The pinholes only allow the passage of light which is perpendicular to the lens, and thus does not need to be bent prior to being focused onto the retina. The patient is instructed to view the Snellen chart with the pinholes up (below left) and then again with them in the down position (below right). If the deficit corrects with the pinholes in place, the acuity issue is related to a refractive problem.

Observation of External Structures:

1. Occular Symmetry: Occasionally, one of the muscles that controls eye movement will be weak or foreshortened, causing one eye to appear deviated medially or laterally compared with the other.

   

2. Eye Lid Symmetry: Both eye lids should cover approximately the same amount of eyeball. Damage to the nerves controlling these structures (Cranial Nerves 3 and 7) can cause the upper or lower lids on one side to appear lower then the other.

   

   Patient unable to completely close left upper eyelid due to peripheral CN 7 dysfunction.

3. Sclera: The normal sclera is white and surrounds the iris and pupil. In the setting of liver or blood disorders that cause hyperbilirubinemia, the sclera may appear yellow, referred to as icterus. This can be easily confused with a muddy-brown discoloration common among older African Americans that is a variant of normal.
   Icteric Sclera
   
   Muddy Brown Sclera
   

4. Conjunctiva: The sclera is covered by a thin transparent membrane known as the conjunctiva, which reflects back onto the underside of the eyelids. Normally, it's invisible except for the fine blood vessels that run through it. When infected or otherwise inflamed, this layer can appear quite red, a condition known as conjunctivitis. Alternatively, the conjunctiva can appear pale if patient is very anemic. By gently applying pressure and pulling down and away on the skin below the lower lid, you can examine the conjunctival reflection, which is the best place to identify this finding.

   Normal Appearing Conjunctival Reflection, Lower Lid	Pale Conjunctiva, due to severe anemia.

   

   Conjunctivitis

   Blood can also accumulate underneath the conjunctiva when one of the small blood vessels within it ruptures. This may be the result of relatively minor trauma (cough, sneeze, or direct blow), a bleeding disorder or idiopathic. The resulting collection of blood is called a subconjunctival hemorrhage. While dramatic, it is generally self limited and does not affect vision.

   Subconjunctival Hemorrhage
   

   

5. Pupil and Iris: Normally, both of these structures are round and symmetric.

When performing the rest of the exam, make sure that you are in a comfortable position. The critical maneuver is assuring that the patient is seated at a height such that their eyes are essentially on the same level as your own when you are standing next to them.

Testing Extra-Occular Movements: Instruct the patient to follow your index finger with their eyes only (i.e. their head remains in one position) as you first move it to either the extreme right or left. Then, once you have the patient looking out laterally, have them follow your finger as you move it first up, then down. Now move your finger across to the other side and repeat. Your path should trace out the letter H. At the end, bring your finger directly in towards the patient's nose. This will cause the patient to look cross-eyed and the pupils should constrict, a response referred to as accommodation.

Tracing out this path allows you to test each of the extra-occular muscles individually and avoids movements that are dependent on more then one muscle, as occurs if you have the patient look up or down while the pupil is oriented straight ahead. Assessments of both extra-occular movements and visual acuity are actually tests of cranial nerve (CN) function. CNs 3, 4, and 6 control movement and CN 2 vision. As these nerves are critical to eye function, it makes sense to evaluate them at this stage rather then during the neurological examination.

Testing Extra Occular Movements

CNs and the Muscles That Control Extra Occular Movements

The cranial nerves and the muscles that they innervate can be remembered using the following mnemonic: SO '4', LR '6', all the rest '3.' Each CN permits the following movements:

• CN 4: Innervates the superior oblique muscle. Allows you to move either eyeball down and inward.
• CN 6: Innervates the lateral rectus muscle. Allows you to move either eyeball laterally.

  Patient with non-functional left 6th cranial nerve. He cannot move left eye all the way to the left.

  
  

CN 3: Innervates the remaining extra occular muscles as well as the upper eye lid. Therefore allows eyeball movement in all remaining directions as well as lifting of the upper lid. The dilation is due to disruption of the parasympathetic fibers which run along the outside of CN3.

Right CN3 Lesion: Note patient's right eye is deviated laterally and there is ptosis of the lid (picture on left), and the right pupil (middle picture) is more dilated than the left pupil (picture on far right).

Disorders of eye movement can also be due to problems with the extraocular muscles themselves. For example, pictured below is a patient who has suffered a traumatic left orbital injury. The inferior rectus muscle has become entrapped within the resulting fracture, preventing the left eye from being able to look downward.

Entrapment of Left Inferior Rectus Muscle

Simulation of extra occular movement and pupillary disorders. from UC Davis.

Visual fields: The normal visual field for each eye extends out from the patient in all directions, with an area of overlap directly in front. Field cuts refer to specific regions where the patient has lost their ability to see. This occurs when the transmitted visual impulse is interrupted at some point in its path from the retina to the visual cortex in the back of the brain. You would, in general, only include a visual field assessment if the patient complained of loss of sight; in particular "blind spots" or "holes" in their vision.Visual fields can be crudely assessed as follows:

1. The examiner should be nose to nose with the patient, separated by approximately 8 to 12 inches.
2. Each eye is checked separately. The examiner closes one eye and the patient closes the one opposite. The open eyes should then be staring directly at one another.
3. The examiner should move their hand out towards the periphery of his/her visual field on the side where the eyes are open. The finger should be equidistant from both persons.
4. The examiner should then move the wiggling finger in towards them, along an imaginary line drawn between the two persons.The patient and examiner should detect the finger at more or less the same time.
5. The finger is then moved out to the diagonal corners of the field and moved inwards from each of these directions. Testing is then done starting at a point in front of the closed eyes. The wiggling finger is moved towards the open eyes.
6. The other eye is then tested.

Meaningful interpretation is predicated upon the examiner having normal fields, as they are using themselves for comparison.

If the examiner cannot seem to move their finger to a point that is outside the patient's field don't worry, as it simply means that their fields are normal.

Interpretation: This test is rather crude, and it is quite possible to have small visual field defects that would not be apparent on this type of testing. Prior to interpreting abnormal findings, the examiner must understand the normal pathways by which visual impulses travel from the eye to the brain.

For more information about visual field testing, see the following links:

Washington University, review of visual field of testing and pathology

University of Arkansas, gross anatomy of visual pathway

Using the Opthalmoscope

This aspect of the exam is, at least initially, quite awkward. Don't worry, it will get easier with practice! Take some time to play with your scope, paying attention to its assembly, on/off mechanism as well as the various lens and light settings which can be utilized. There are a number of different brands on the market and each is a bit different. For the purposes of the general exam, we'll focus on the simplest settings and most basic techniques.

Side of Scope Facing Examiner

Side of Scope Facing Patient

Assessing Pupillary Response to Light:
The normal pupil constricts when either exposed directly to bright light or when that same light is presented to the other eye, referred to as the consensual response. This is due to the fact that stimulation of the afferent (i.e. sensory, carried with CN 2) nerves in one eye will trigger efferent (i.e. motor, carried with CN 3) activation and subsequent constriction of the pupils of both eyes. Disease affecting either the efferent or afferent limbs will alter these responses accordingly. Also, processes which raise intracranial pressure (e.g. brain tumors, collections of blood) can cause CN 3 dysfunction, resulting in dilatation of the pupils and uresponsiveness to direct stimulation by light. To assess pupillary reactions, proceed as follows:

1. Instruct the patient to look towards a distant area in the room (e.g. the corner where the wall and ceiling meet) while keeping both of their eyes open. You may need to gently remind them throughout the exam to continue looking in that direction as it is very difficult to examine a roving eyeball. Do not ask them to focus on a specific object as this will lead to pupillary constriction.
2. Turn on your opthalmoscope and adjust the light intensity to mid-range power. The cone of light produced should be a white, medium sized circle. Circle sizes available include small, medium and large. If possible, turn off most of the lights in the room. This allows the pupil to dilate and cuts down on reflections from the surface of the eye.
3. Make note of the size and shape of each pupil. Then assess whether each pupil constricts appropriately in response to direct and indirect stimulation. If you're having trouble detecting any change, have the patient close their eye for several seconds and place your hand over their eyebrows to provide additional shade. This helps to make it as dark as possible, encouraging greater pupillary dilation and therefore accentuating any change which may occur after light is introduced. It may be hard to detect the consensual response if the lighting in your room is sub-optimal (i.e. if it's too dark, you won't be able to see the other eye). Note that you do not need to look through the viewing window of the scope to perform this part of the exam as you are essentially using it as a flashlight.

Closer Exam of the Outer Structures of the Eye:

1. Every opthalmoscope has a mechanism for changing the viewing lens. These lenses vary in their ability to bend light and are numbered and color coded. The specific lens that allows you to see something in focus will vary with your distance from that structure as well as the refractive error of both your eyes and the patients. To better examine the sclera, conjunctiva, pupil, cornea or iris, start with the lens identified by a green 4 or 6.
2. Now grasp the handle with your right hand (the following instructions are for examining the patient's right eye) such that your middle finger is resting on the lower, front aspect of the head of the opthalmoscope.
3. Bring your right eye up to the viewing window. While you can either wear or remove your own glasses, the patient's should be taken off. It's OK to leave contacts in place.
4. Take your left hand and place it on the patient's forehead and gently apply upward traction on the top lid with your thumb. This will "remind" them not to blink and let you know their precise location. Obviously, try not to poke them in the eye with this finger! Alternatively, you can place your left hand on the patient's shoulder as a means of keeping track of their location. Try to keep both of your eyes open when performing the exam as you might find it quite tiring to continually squint with the non-examining eye.
5. Start approximately 15 cm from the patient and approach from about 15 or 20 degrees to the left of center. When you look through the viewing window, the outer structures of the eye should come into sharp focus. If not, slowly move closer or further from the patient until these structures become clear. It takes a bit of experimentation to find the lens that is right for any given distance, so make lens changes slowly by rotating the adjustment wheel. There is no magic way of guessing which lens will allow the sharpest view.

*Most clinicians don't perform a detailed examination of the outer structures of the eye if the patient has neither obvious abnormalities nor complaints referable to this region.

Viewing the Fundus (the retina and associated structures):

Repeat steps 1 thru 5 as above. Adjust the lens selection wheel so that 0 appears in the display window.

Red Reflex

Look through the viewing window at the patient's pupil, using your right eye to examine their right eye. You should see a sparkly, orange-red color known as the red reflex. This is caused by light reflecting off of the retina and is the same phenomenon that produces red eyes in flash photographs. Occasionally, the translucent structures which allow light to pass unimpeded from outside the eye to the retina become opacified and the red reflex is lost. In adults, this is most commonly associated with cataracts, a process caused by clouding of the lens.

Eye Cross Section
(Picture Courtesy of Ray Kelly)

3. In order to see the fundus in greater detail, you will need to move very close to the patient, analogous to looking through a key hole (i.e. the closer you are, the more you'll see). Your middle finger, the one resting on the low front of the head piece, should be on or near the patient's cheek. Starting with the 0 lens in place, rotate the adjustment wheel counter clockwise. If you change lenses too quickly, you'll probably whizz right by the one that gives the sharpest picture, so be patient. In the event that this does not bring anything into focus, trying rotating the adjustment wheel in the opposite direction. It doesn't really matter what number lens is required to achieve the clearest view. Again, this will vary with the refractive error of both you and the patient. The numbers are simply provided for reference. Thus, while you may be able to see the fundus of some patients with the green numbers still visible, you will need red 8 or 10 to visualize the same region in a different person. Once you're close in and have the retina in clear view, you should only need to change the lens one or two clicks in order to keep all structures in focus as you scan across.
4. You will only be able to see a relatively small segment of the retina at any one time. Your initial view will probably be of blood vessels on a random patch of retina (see below).

The retina has a refractile, orange-red appearance, varying a bit with the skin color and age of the patient. Fundoscopy provides important information as it not only enables you to detect diseases of the eyes but is also the only area of the body where small blood vessels can be studied with relative ease. There are a number of chronic systemic diseases (most commonly hypertension, diabetes and atherosclerosis) that affect vessels of this size in a relatively slow and silent fashion. It is, however, frequently impossible to directly assess the extent of this damage during physical examination as the affected organs, e.g. kidneys, are well hidden. Evaluation of the retina provides an opportunity to directly visualize these processes. Based on this information, clinicians can make educated guesses as to what is occurring elsewhere in the body. Having said this, do not be discouraged if it takes a while before you're able to identify structures with any degree of confidence. Practice on every patient that you examine. It will come with time. A few things to pay attention to:

1. When you first visualize the retina, you will note branching blood vessels. The bigger, darker ones are the veins and the smaller, brighter red structures the arteries. Changes in the appearance of the arteries (copper wiring) as well as alterations in the arterial-venous crossing pattern (a-v nicking) occur with atherosclerosis and hypertension respectively (see any text for pictures). These vessels are more obvious in the superior and inferior aspects of the retina, with relative sparing of the temporal and medial regions.
2. Imagine that the blood vessels are the branches of a tree. Follow them in a direction that leads to less branching (i.e. towards the trunk). This will direct you towards the optic disc, the point at which the vessels enter the retina along with the head of the optic nerve. The edges of this round disc are sharp and well defined in the normal state. It should be a bit more yellow/orange when compared to the rest of the retina. At the center of the disc is the optic cup, a distinct circular area from which the blood vessels actually emerge. The disc is not located in the exact center of the retina but rather towards its medial/nasal aspect. Measurements in the eye are made using disc size as a measuring device (e.g. a finding may be described as being at 2 O'clock, 2 disc diameters from the center of the disc). If you are unable to locate the disc after following the vessels in one direction, simply head the other way.
3. The macula is a region located lateral to the optic disc. It looks somewhat darker then the rest of the retina and, as opposed to the disc, has no distinct borders. The macula provides the sharpest vision. It can be best visualized by asking the patient to stare directly at the light of the opthalmoscope while you remain focused on a fixed area of the retina.
4. You will not be able to visualize the entire retina at any one time (approximately one disc diameter should be visible). To view different areas, you'll have to shift the angle with which you peer through the pupil. This requires very small movements. Try to examine the entire structure systematically, looking up, down, left and right. You will undoubtedly have to remind the patient to continue looking straight ahead, else the fundus will be in continual motion and you will have no chance of finding anything. It's also a good idea to periodically give the patient a break (particularly if the exam is taking a while), allowing them to blink in the dark before resuming.

Retina--Right Eye
(Picture Courtesy of Ray Kelly)

In order to view the patient's left eye, grasp the scope in your left hand and use your left eye; then repeat the process described above.

If possible, try to avoid eating garlic, onions or other strong smelling food. If you are "dependent" on these substances, invest in a box of tic-tacs for use during the exam!

It is much easier to examine the retina after the pupil has been pharmacologically dilated. In actual practice, however, most providers, with the exception of optometrists and ophthalmologists, do not routinely perform dilated eye exams. This is because dilation takes time and is a bit uncomfortable for the patient as it causes increased light sensitivity that lasts for several hours. Additionally, a non-dilated view of the retina is adequate for a general exam in which the patient has no specific ophthalmologic complaints. Take advantage of any opportunity to perform an examination through a dilated pupil as this is a great way of learning. Make use of additional reference texts, paying particular attention to color photos depicting variants of normal as well as the findings associated with common disease states.

The following links provide excellent images of assorted ophthalmologic pathology.

Atlas of Ophthalmologic Images

Digital Atlas of Ophthalmology, NY Eye and Ear Infirmary

Eye Atlas (Best when viewed with Internet Explorer), Johns Hopkins University