This is a 6 month old baby girl who comes to your office for a well child examination. She has had no problems in the past with her eyes and according to her parents, she tracks well and reaches for objects. Her parents deny any crossing of the eyes when she looks at objects from a distance; however, her mother mentions that she had a lazy eye when she was a child and needed to be operated on.

Exam: Vital signs are normal for age. Her red reflex and corneal light reflex test are normal. Cover test is negative for strabismus. Her extraocular movements appear intact and she is able to follow objects 180 degrees.

You conclude that her eye examination is normal and reassure the mother. You schedule her next appointment when she is 9 months old or earlier if her mother notices a problem.

The examination of the eye is an essential part of an examination since disease or pathology of the eye can result in vision loss. Although there are diseases that are easily noticed, such as conjunctivitis, there are other conditions that are much more subtle. These conditions include leukokoria of retinoblastoma and strabismus that can lead to amblyopia. Without a careful examination of the eyes, these problems can be missed and result in blindness. There are times that patients will come to us because of pain, itchiness, blurriness, redness, or discharge of the eye. As primary care physicians, we should be comfortable with the eye examination to be able to correctly diagnose, treat, or refer our patients for specialty care by an ophthalmologist. This chapter will focus on screening of the eye in the well child since some serious conditions can only be detected early enough through screening.

In order to know how to examine the eye, a basic knowledge of the anatomy of the eye is important. It would be helpful to refer to a diagram of the eye. The eye is made up of three coats. The outer part is the sclera, which is a white shell of the eye, and the cornea. Next comes the uvea, which is made up of the choroid, the ciliary body, and iris. The choroid is a vascular layer between the retina and sclera. The ciliary body, which produces aqueous humor, is on the sides of the lens that focusses the lens. Immediately anterior to the lens is the iris, which is a colored diaphragm that contracts or dilates and regulates the amount of light entering through the lens. And the innermost part is the retina, which contains rods and cones. A part of the retina is the macula, which is minimally vascular and is responsible for the most acute vision. A pit in the middle of the macula is the fovea, which corresponds to the central fixation of vision. Medial to the macula is the optic nerve, which transmits signals from the retina to the brain. There are two chambers, the anterior and posterior chamber, which are divided by the lens. The lens is a media that focusses light. The anterior chamber is between the cornea and the lens, and is filled with the aqueous humor, which is a clear fluid. The posterior chamber contains the vitreous humor, which is a clear jelly filling. The conjunctiva is a mucus membrane that covers the anterior portion of the sclera (bulbar conjunctiva) and the inner part of the eyelids (palpebral conjunctiva).

There are six extraocular muscles that move the eye. They are the superior, inferior, medial, and lateral rectus muscles, and the superior and inferior oblique muscles which are innervated by cranial nerves 3, 4, and 6 (1,2).

The examination of the well child is primarily dependent on his or her age since infants and young children are less cooperative with the examination compared to older children. Also, screening for specific problems is essential at an early age to prevent vision problems later in life.

From birth to 6 months of age, screening tests that can be done are the red reflex, corneal light reflex, and external examination. An infant's eyes are examined from a distance with an ophthalmoscope to look for a red reflex. If the pupillary light reflex (also known as the red reflex) is totally absent in one or both eyes, then corneal opacity, cataracts, retinal detachment, or a large hemorrhage should be suspected. If a pupillary light reflex is present, but it is white (i.e., not red), this is called leukokoria and retinoblastoma should be suspected. Retinoblastoma is often detected by parents when viewing flash photographs of their infant when a white eye reflex is noted while everyone else in the photo has a "red eye". Ideally, the physician should notice this on routine screening before this happens.

Many times, an infant's eyes are closed during the first several days of life. One trick to having them open their eyes is to gently swing them from a vertical to semi-upright position. Turning off the lights would also help dilate the eyes to make the red reflex easier to see.

Another is the corneal light reflex test in which the eyes are viewed with an ophthalmoscope to see if the corneas are symmetrical. The reflection of the light off the cornea should be symmetric. Asymmetry could signify strabismus and warrants a referral to an ophthalmologist.

In doing the external examination, the orbits and globes are examined for symmetry in terms of shape, position, and movement. The eyelids are likewise noted for symmetry and movement. Asymmetry may signify proptosis, cranial nerve palsy, or lid masses (3). Note if the pupils are round and symmetrical. Irregularity could signify an iris coloboma, which is a "keyhole" shaped defect, caused by an embryological defect of closure of the eye. In a child with choanal atresia and ear anomalies, a coloboma (eye defect) can be part of CHARGE syndrome. Corneal size should be assessed since large corneas, together with excessive tearing and photophobia is a sign of infantile glaucoma.

From birth to 3 months of age, healthy infants can appear to have disconjugate or uneven gaze. However, constant jiggling of the eyes, or nystagmus, is abnormal at any age. Scleral or retinal hemorrhages in neonates can occur as part of birth trauma, and will resolve on its own. The color of the sclera should also be noted, since a blue sclera, in addition to multiple bone fractures can signify osteogenesis imperfecta. Also a yellow sclera or icterus can be seen in jaundiced babies. At times, there is mucoid discharge around the medial canthus of the eye, which can be due to nasolacrimal duct obstruction. This problem is corrected by massaging the duct, and most of the time, this will resolved by 1 year of age. However, if it continues past a year, then an ophthalmological referral should be considered for probing and dilation of the nasolacrimal duct.

Visual acuity can be assessed by having the child regard a face or track a brightly colored object. Babies seem to notice faces more than other objects, especially faces that are smiling and showing teeth. At birth, they should be able to focus on a face at about an arm's length away, which is their point of focus (4). At 1 month of age, they can follow to the midline. At 2 months of age, they can follow an object past midline, and at 5-6 months of age, they can follow to 180 degrees (5). It should also be noted that they are very far-sighted at this age.

From 6 months to 4 years of age, in addition to the methods described for the birth to 6 month old, the Cover Test can be used to assess strabismus and vision. This test is done by covering one of the eyes and seeing if the opposite (uncovered) eye shifts, or when uncovered, if the same eye refocusses (this eye shifts away when covered). The best way to do this is to have the child focus on something at a distance (such as a light), and using your thumb as the occluder while holding the head still with your hand so that it does not move. Before doing the Cover Test, the corneal light reflex can also be done to assess for strabismus, and is less intimidating. The parents or caretakers can be questioned regarding whether they notice one eye being "crooked" when the child looks at something. A note of warning is that "crooked eyes" can be mistaken for pseudostrabismus, especially in a child with epicanthal folds. Pseudostrabismus can be differentiated from true strabismus by the aforementioned tests.

Visual acuity can be assessed by having them follow a face or object, or by testing for optokinetic nystagmus. This is done by having the child look at a slowly rotating drum or cloth with alternating black and white stripes (or colored and white stripes) and noting if the normal nystagmus with this stimulus is present. The two phases of this normal nystagmus are a slow phase when the eyes focus on the target, and a quick, jerky phase when the eyes return to the subsequent target. The drum or cloth should be about an arm's length away. Also, the red reflex should be assessed at this age. Extraocular muscles can be assessed in one of several ways. One is by spinning which is used for infants. What this entails is holding the child up and turning your body several times in one direction, then in the opposite direction, while watching the child's eyes. Another way is to have a child track an object in an imaginary rectangle around his face. Lastly, turning the head quickly will elicit eye movements through vestibular means, although the child will be angry afterwards (4).

From 4 years of age and onward, the eye exam can be performed the same as in adults. Besides looking at the pupils and assessing extraocular movements, funduscopy can be done, and can even be performed in younger children. Although the older child can be cooperative and focus on a stationary object while you view his fundus, in the younger child, funduscopy can be a frustrating experience. One method would be to stay still while viewing the eye, and have the child move his eye for you on his own. When you are about 12 inches away, note if the red reflex is equal in all four quadrants of the fundus. As you get closer, view the optic disk as it passes by. Lastly, look at the bright fovea reflection by telling the child to look at your magic light. Make sure you have the lights off to have maximum pupillary dilatation.

Visual acuity can be assessed by several means, such as having a wall mounted Snellen chart or "E" chart (4). There are also charts available that can be viewed through a desktop instrument. A more technologically advanced tool is Welch Allyn's SureSight Vision screener, which can provide objective data in 5 seconds without any cooperation from the patient; however, it costs about $4,500 in 2002 (6). Keep in mind that an acuity of 20/40 is generally accepted as normal for 3 year olds, 20/30 typical for 4 year old, and 20/20 vision attainable by most 5 to 6 year old children. Referral to an ophthalmologist is indicated if the vision is 20/50 or worse in a 5 year old child, and 20/40 or worse in a 6 year old child (3).

The eye examination is one of the most difficult, yet rewarding experiences in pediatrics. Unfortunately, the only way to become proficient, is to do as many as possible. Remember to do the least intimidating step first (which may be external observation or assessing the red reflex or corneal light reflex), and the most intimidating test last (such as the funduscopic exam). With practice and diligence, the eye examination will become easier and the rewards for discovering preventable pathology that much greater.

Questions

1. What is the differential diagnosis of an absent pupillary light reflex (red reflex)?

2. What condition causes leukocoria?

3. A parent is worried that her Asian baby has crooked eyes. How would you assess whether this is pseudostrabismus?

4. What is the distance of focus for infants?

5. At what age can an infant follow an object to the midline, past the midline, and 180 degrees?

6. How can you assess extraocular movements in the uncooperative or young child?

7. What is one way you can look at the fundus in the uncooperative child?

References

1. Davis FA. Taber's Cyclopedic Dictionary, 16th edition. 1985, Philadelphia: F.A. Davis Company, pp. 643-644.

2. Leitman, MW. Manual for Eye Examination and Diagnosis, 5th edition. 2001, Massachusetts: Blackwell Science, Inc., ii.

3. Olitsky SE, Nelson LB. Chapter 626-Examination of the Eye. In: Behrman, et al (eds). Nelson Textbook of Pediatrics, 16th edition. 2000, Philadelphia: W.B. Saunders Company, pp. 1896-1897.

4. LaRoche GR. Chapter 7-Examining the Visual System in Children. In: Goldbloom RB (ed). Pediatric Clinical Skills. 1992, New York: Churchill Livingstone, pp. 125-152.

5. Bravo AM. Development. In: Siberry GK, Iannone R (eds). The Harriet Lane Handbook, 15th edition. 2000, St. Louis: Mosby, Inc., pp. 187-206.

6. Welch Allyn Medical Products, 2002. www.welchallyn.com.

Answers to questions

1. Cataracts, retinal detachment, and other pathology that is obscuring the vitreous or aqueous clarity.

2. Retinoblastoma.

3. Performing a Cover Test and corneal light reflex test.

4. About an adult's arm length.

5. To the midline is 1 month, past the midline is 2 months, and 180 degrees is 5-6 months.

6. Two methods are to spin the child and turning his head, both of which use the vestibular systems.

7. By being patient, looking at the child's red reflex in all four quadrants in a stationary position from about 12 inches away, and as you move closer, viewing the optic disk as it passes by, and lastly the fovea by telling the child to look directly at your "magic light."